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Continued improvements of inventory methodologies: Task 4.1 Improving the quality of SOx/SO2 estimates and reporting ___________________________________________________

European Commission Ref. 070201/2014/693666/FRA/ENV.C.3

ED 60437_Task 4.1 | Issue No. 4 | Date 20/05/2016

Continued improvements of inventory methodologies: Task 4.1 | i

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Author:

Chris Green, Maria Pooley, Will Smith, Robert Whiting (Amec Foster Wheeler), Chris Dore (Aether)

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Ricardo Energy & Environment reference:

Ref: ED60437_Task 4.1: Issue No. 4

Ricardo Energy and Environment

Task 4.1 Improving the quality of SOX/SO2 estimates and reporting

March 2016

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Document revisions

No. Details Date

1 Final version 08/03/2016

2 Final version with additional edits to ensure executive summary and conclusion are fully harmonised

18/03/2016

3 New Appendix added to include further discussion regarding the policy history for sulphur reporting

05/05/2016

4 Further minor changes to editorial content

17/05/2016



Executive summary

The emission of sulphur in various forms to air poses a threat to human health and the environment. Within

the atmosphere sulphur forms sulphur oxides (SOX), which refers to many types of sulphur and oxygen

containing compounds, the two major ones being sulphur dioxide (SO2) and sulphur trioxide (SO3). This

includes direct health effects upon humans above certain atmospheric concentrations of SO2 and the

potential for acid deposition which can have negative effects upon the environment. This latter aspect raised

international recognition for the possibility of long-range transboundary effects of sulphur emissions in

countries other than the point of emission. This issue particularly came to prominence in the 1970s with the

phenomenon termed ‘acid rain’ which had a direct impact upon Scandinavian countries and emissions from

industrial point sources in Western Europe.

The air quality issues posed by sulphur are such that international action has been taken to mitigate them.

This included the creation of the UNECE 1979 Convention on Long Range Transboundary Air Pollution

(CLRTAP) and the formation of a series of protocols, including the 1999 Gothenburg Protocol, specifically to

address sulphur and its environmental and health effects. In some cases there are specific provisions of

SO2 such as in CLRTAP (Article 8 Subparagraph a) on reporting SO2 emissions and for source-specific SO2

limit values (e.g. the Gothenburg Protocol). At EU level there have also been moves to implement measures

to control and reduce the emissions of sulphur through the creation of the National Emission Ceilings

Directive (NECD) (2001/81/EC). Salient to both CLRTAP and NECD is the need to estimate and report on

emissions in order to assess progress towards emissions reduction. However an issue exists in the way that

‘sulphur’ is calculated and reported under the CLRTAP and the NECD which poses an issue for

comparability and emissions gaps within reporting.

The current study has reviewed and assessed the definitions, and magnitude of different forms of sulphur in

major emission sources that would affect the international reporting carried out by Member States. The

NECD does not define ‘sulphur’ as such, but specifies reporting and emission targets for SO2 only. Article 1

of the Gothenburg Protocol defines ‘Sulphur’ as ‘all forms of sulphur expressed as sulphur dioxide (SO2)’.

This would suggest at face value that reporting and obligations of meeting the sulphur ceilings set out in

annex II of the original Gothenburg protocol should include sulphur dioxide, sulphur trioxide (SO3) and other

forms of sulphur emissions, including reduced sulphur. However, the specific emission limit values for

source categories set out in the Gothenburg Protocol annexes IV are set for SO2 (not total sulphur), except

for the limit value for titanium oxide production in the 2012 amendment to the Protocol where the limit value

is set for SOX (expressed as SO2). It should here be noted that the protocols (or separate decisions of the

CLRTAP) do not provide an explicit definition of SOX, thus it has been interpreted as the oxidised form of

sulphur or all forms of sulphur compounds depending on the circumstances.

Additionally however, as the Gothenburg Protocol has evolved (latest version 2012), it has harmonised the

elements of the Gothenburg Protocol with the NECD and other international legislation which is only SO2

focused.

This means there is a lack of clarity with regard to whether “SO2” means specifically sulphur dioxide, all

forms of oxidised sulphur, or all forms of sulphur expressed as SO2.

A review of related legislation and major references open to inventory compilers suggested that the majority

of available reference material is focused specifically on SO2. Along with the NECD, other EU legislation

including the Ambient Air Quality Directive (2008/50/EC), Mechanisms for Monitoring and Reporting of

Greenhouse Gas Emissions (525/2013/EU) and Industrial Emissions Directive (2010/75/EU) all refer to

sulphur dioxide only. In contrast the UNFCCC Kyoto Protocol and UNFCCC guidance for inventory

compilation, refer to sulphur as sulphur oxides, and are in that way different to the EU Mechanism for

Monitoring and Reporting of Greenhouse Gas Emissions. The MARPOL Convention for international

shipping refers to SOX throughout, but in setting compliance limits for emissions defers to the International

maritime organisation (IMO) which uses only SO2. The Kiev Protocol of the Aarhus Convention on Pollutant

Release and Transfer Registers (also transposed into the PRTR Regulation EC/166/2006) quotes SOX and

SO2 interchangeably. The EMEP Corinair (now the EMEP/EEA) guidebook, which is the major reference for

CLRTAP, refers to the NECD (SO2 only) and Gothenburg Protocol (all sulphur expressed as SO2), including



a section on the history of the guidebook. Emission factors within the guidebook are quoted as SOX to keep

alignment with the 1999 Gothenburg Protocol.

A review of the major emission sources reported by EU Member States 2010 to 2013 under the NECD and

the CLRTAP based on the Nomenclature for Reporting (NFR) index system shows a high level of correlation.

While the main sources of emissions are broadly the same for LRTAP (SOX) and NECD (SO2) reporting,

there are some differences in reported emissions and in the relative contribution of the sector. The most

notable differences for reported emissions are for 1A3di(i) International maritime navigation, 1A2gviii

Stationary combustion: Other and 1A2f Stationary combustion: Non-metallic minerals.

Based on a review of the available literature the proportion of SO2, SO3 and other forms of S within total

sulphur emissions have been assessed within the major point sources for combustion of fuels. This review

indicated that for major point sources, SO2 represents 95% or greater of the total sulphur emission. Sources

do exist for emissions of sulphur from non-combustion point sources, such as refinery and iron and steel

plant. While these sources will report under the Industrial Emissions Directive, less is known about the ratio

of SO2 and SO3 within SOX.

A review of other forms of sulphur potentially released from industrial processes was also carried out. This

reflects the potential for emissions of a wide number of other species of sulphur which can contribute to the

overall sulphur budget. This includes:

Hydrogen sulphide - H2S

Methyl mercaptan - CH3SH

Dimethyl sulphide - C2H6S

Dimethyl disulphide - (CH3S)2

Carbon disulphide - CS2

Carbonyl sulphide - COS

Sulphuric acid 1 - H2SO4

Sulphite/Hydrosulphite/Bisulphite - SO32- / HSO3

- / S2O42-

However, while a number of sulphur species other than SO2 can be emitted from point sources, the review of

literature still suggests that the combined emission equates to less than 5% of the total sulphur emitted.

The study has also assessed the effects of abatement technologies on the sulphur compounds ratios, and

likely implications for SO2, SO3 and other forms of S within the emission. Selective Catalytic Reduction

(SCR) can increase in the amount of SO3 produced, due to the fact that as NOX is reduced to nitrogen and

water by the reaction with ammonia (NH3) in the presence of a catalyst, meaning that a small fraction of SO2

is oxidized to SO3. SO3 can be further converted through reaction with water into sulphuric acid (H2SO4), one

of the other forms of sulphur mentioned, in the air heater of a power plant. Further guidance from CLRTAP2

recognises that SO2 is created from the combustion of fuels containing sulphur, often in large point sources,

while SO3 is created by oxidation during abatement processes. During Flue Gas Desulphurisation (FGD, the

final stage of abatement before atmospheric release of emissions), wet lime/limestone scrubbers can remove

92-98% of both SO2 and SO3, while dry limestone scrubbers can remove 85-92% of SO2 and 95% of

SO3.This would suggest that in the presence of FGD technologies, while the absolute concentration of SO3 is

reduced, the ratio of SO3:SO2 is driven more strongly towards SO2 in the presence of dry scrubbers than the

far more ubiquitously used wet scrubbers3, but again, the overall sulphur emission is still dominated by SO2

at or greater than 95%.

1 S is not in a reduced state in H2SO4. While it may be removed by certain methods such as NCASI Method 8A, it is included here because it may not be captured by some SO2 measurement techniques. 2 UNECE, 2015, ‘Guidance document on control techniques for emissions of sulphur, nitrogen oxides, volatile organic compounds and particulate matter (including PM10, PM2.5 and black carbon) from stationary sources’ 3 European Commission. 2013. Integrated Pollution Prevention and Control BREF, Large Combustion Plants.



The conclusion of the study has identified that there is a compatibility issue in the ways that sulphur

compounds are recognised between CLRTAP and the NECD. However there is also a weight of supporting

legislation at EU level and internationally which strongly favours SO2 as the recognised pollutant for emission

estimation and hence for compliance checking with reduction targets and limit values. Assessment of SO2 to

total S ratios suggest that SO2 is the dominant form in combustion emissions at 95% or greater, which would

still leave an emission gap of c.5% for other forms of sulphur under the CLRTAP definition. Three options to

address this issue are therefore suggested:

Option 1: Amendment of the Gothenburg Protocol Article 1 to amend the definition of ‘sulphur’ to

bring in it alignment with the NECD and related legislation. This option would remove any ambiguity

in the definitions and resolve potential compatibility issues assuming that a number of inventories will

be based on SO2 only. However this option would also exclude SO3 and non-oxide forms of sulphur

which do contribute to the overall atmospheric emissions budget and sulphur deposition. It should

be noted that the Gothenburg Protocol as amended still refers to "sulphur" with regard to the

indicative reduction commitments for the USA (footnote to annex II, table 2), whereas the revised

(amended) annex II refers to SO2 only.

Option 2: Amendment of the National Emission Ceilings Directive to amend the definition of ‘sulphur’

to bring it into alignment with the Gothenburg Protocol. This option would remove any ambiguity in

the definitions and resolve potential compatibility issues assuming that a number of inventories will

be based on all forms of sulphur expressed as SO2. While this option would close a data gap and

ensure continuity between the Protocol and Directive, it may have consequences for emissions

targets for some EU Member States. Where emission ceilings have been agreed, revision of the

definitions and need for additional work to revise inventories to include missing non-sulphur dioxide

proportions may mean that some Member States are no longer able to meet the previously agreed

targets.

Option 3: Develop the guidance provided by TFEIP and EMEP to Inventory compilers to remove

ambiguity. This option can work one of two ways, either there is an agreement that "sulphur"

principally means SO2, and therefore inventories should be based on SO2 to ensure comparability

between each other and NECD. The second method would be to enforce the article 1 definition and

make clear within the guidebook where emission factors are SO2 only and where emission factors

are for sulphur emissions expressed as SO2. This could mean the need for additional reference to

reflect SO2 and total sulphur within the guidance. This option would ensure continuity for reporting

under CLRTAP and help define the difference between CLRTAP and NECD estimates. However it

may also represent the need for revisions of both existing inventories and the guidelines for reporting

and the EMEP/EEA guidebook itself.

Option 4: Agree to interpret the 2012 amendment of the Gothenburg Protocol as only referring to

obligations for total sulphur for the 2020 reduction commitments and align EU legislation thereto.

This would require agreeing an interpretation of the CLRTAP modifications, also with other non-EU

parties of those alterations.

Option 5: Recognise that differences exist within the interpretation of how ‘sulphur’ is defined for

estimation and reporting under different international policy instruments; but take no further action on

the basis that the impact on overall reported emissions is likely to be small for most countries and

sectors.



Contents

1. Introduction 8

2. Review of the reporting requirements for NECD, CLRTAP and related policy 9

2.1 Introduction 9 The National Emission Ceilings Directive (2001/81/EC) 9 The UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP) 9 The EMEP Air Pollutant Inventory Guidebook 10 The United Nations Framework Convention on Climate Change (UNFCCC) and Kyoto Protocol 11 The International Convention for the Prevention of Pollution from Ships, MARPOL 11 Additional EU policies and legislation 12 Summary 13

3. Development of non-Sulphur Oxide emission estimates 14

Hydrogen Sulphide (H2S) 14 Methyl Mercaptan (CH3SH) 15 Dimethyl Sulphide (C2H6S) 15 Dimethyl Disulphide (CH3S)2 15 Carbon Disulphide (CS2) 15 Carbonyl Sulphide - COS 16 Sulphuric Acid - H2SO4 16 Sulphite/Hydrosulphite/Bisulphite 16

3.1 Sources Expected to Emit Reduced Sulphur Compounds 17 Fossil Fuel Extraction 17 Manufacture of Fuels 17 Industrial Processes and Product Manufacture 18 Agriculture 21 Waste 21

4. Comparison of SO2 vs SOX emissions 23

4.1 Introduction 23

4.2 Review of key emission sources for SO2 and SOX 23

4.3 Ratios of sulphur compounds in SOX 24 Chemistry 25 Ratio of sulphur compounds in SOX 26

4.4 Effect of abatement technologies on ratios of sulphur compounds in SOX 27 Formation of SO3 and H2SO4 27 Formation of SO3 in SCR Reactors 28 Flue gas desulphurisation (FGD) and formation of aerosols in wet FGD systems 28 Mitigation of SO3 Emissions 29 Selective non-catalytic reduction 29 Sorbent injection 29

5. Summary and Recommendations 30

5.1 Summary 30

5.2 Recommendations 30

6. References 32



Table 4.1 A list of the 12 highest emitting sectors under the National Emission Ceilings Directive (NCED) and the Convention on Long-range Transboundary Air Pollution (CLRTAP) for 2013. 23 Table 4.2 Main emission sources within the highest emitting sectors 24 Table 4.3 Ratios of SO2, SO3 and other S compounds for high emitting sectors 26

Figure 3.1 Total S emission load (as kg S/tonne of air dried pulp) from major processes (recovery boiler, lime kiln, NCG burner) including uncollected or untreated weak gases (European Commission, 2015) 20 Figure 4.1 SO3/SOX ratio for different oxygen to fuel ratios (Flegg et al. 2013) 25 Figure 4.2 A schematic diagram of SO3 and H2SO4 being formed in a bituminous coal-fired power plant (Murphy, 2007) 28



1. Introduction

The emission of sulphur in various forms to air poses a threat to human health and the environment from the

formation of sulphur oxides (SOX) within the atmosphere. This includes direct health effects upon humans

above certain atmospheric concentrations of SOX and the potential for acid deposition which can have

negative effects upon the environment. This latter part raises international recognition for the possibility of

long-range transboundary effects of sulphur emissions in countries other than the point of emission. This

issue particularly came to prominence in the 1970s with the phenomenon termed ‘acid rain’ which had direct

impact upon Scandinavian countries and emissions from industrial point sources in Western Europe.

Such has been the concern for emissions of sulphur that action has been taken at international level to

control and reduce the emissions of sulphur to the atmosphere. Under the auspices of the UNECE, the

Convention on Long-Range Transboundary Air Pollution (CLRTAP) was created in 1979 and entered into

force in 1983 as a direct response to the issue of transboundary effects and the responsibility of nations to

control emissions which could affect their neighbouring countries. This action further translated into the

formation of the Gothenburg Protocol (1999) specifically to address sulphur emissions, which are largely

dominated by major combustion point sources. Within the European Union, action has also been taken to

help control and curb the emissions of sulphur, again recognising the potential health effects and

transboundary issues. The National Emission Ceilings Directive4 (NECD) (2001/81/EC) adopted in 2001,

sets out to provide targeted reductions of air quality pollutant emissions (including sulphur) based against a

baseline year (not later than 2010).

Key to the success of both CLRTAP and the NECD is the development of emission inventories, and

reporting in order to track and monitor the progress towards emissions reduction. The development of such

emission inventories require a discrete set of skills and experience drawing upon a range of data including

both monitoring but also emission estimates developed through the use of activity and emission factor data.

These reported inventories represent the best estimate for the true environmental releases and assist in the

planning necessary for emissions reduction and targets under the NECD.

However, CLRTAP and the NECD recognise ‘sulphur’ differently which poses an issue of comparability. This

is particularly important where a given nation may use the same emission inventory to satisfy the reporting

for both CLRTAP and the NECD. Equally where major reference sources or guidance in inventory

development are unclear on whether SOX and sulphur dioxide (SO2) are one and the same thing, means that

the development of emission inventories may also have continuity issues which can affect the overall total

emission. This represents an issue for reporting under both CLRTAP and the NECD.

This short report is intended to provide an overview of the issue and will aim to address the following

questions:

What are the specific reporting requirements for sulphur under CLRTAP and the NECD?

How does related policy and key references guidance differ in terms of supporting inventory

compilers when fulfilling the requirements of CLRTAP and the NECD?

How does the issue of non-oxide sulphur compounds, particularly reduced sulphur, contribute to

the total budget for SOX?

How does SO2 and sulphur trioxide (SO3) vary for different point sources? And what does this

mean for the overall completeness and integrity of emission inventories?

4 OJ 309, 27.11.2001, p.30 http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32001L0081

http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32001L0081



2. Review of the reporting requirements for NECD, CLRTAP and related policy

2.1 Introduction

This section will answer the first two aims of the project included within the introduction, namely by assessing

what is specifically stated under CLRTAP and the NECD currently for inclusion as ‘sulphur’ emissions. It will

then move on to review how sulphur is managed under a range of related policy both at EU level but also

under related international conventions; additional information on the policy history for sulphur reporting is

included within Appendix A. Key to this review will be to understand how the related policy and major

guidance documents developed as part of the policy help guide inventory compilers. This is a critical aspect

to the understanding of how inventory compilation teams have been guided when developing emission

inventory estimates for both the NECD and CLRTAP, and how sulphur has been accounted.

The National Emission Ceilings Directive (2001/81/EC)

Under the National Emission Ceilings Directive, ‘sulphur’, is assumed to mean sulphur dioxide. This is stated

within item (11) of the Directive, thus:

“A set of national ceilings for each Member State for emissions of sulphur dioxide, nitrogen oxides,

volatile organic compounds and ammonia is a cost-effective way of meeting interim environmental

objectives. Such emission ceilings will allow the Community and the Member States flexibility in

determining how to comply with them”.

Further to this definition the Directive sets out under article 4 that “by the year 2010 at the latest, Member

States shall limit their annual national emissions of the pollutants sulphur dioxide (SO2).”

On this basis the NECD is clear that the emission of sulphur to the atmosphere is intended to mean sulphur

dioxide only.

In relation to the preparation of inventories, the NECD requires Member States to “prepare and annually

update national emission inventories and emissions projections for 2010, for the pollutants selected. MS

shall establish their inventories and projections using methodologies specified in Annex III” (Article 5).

Annex III requests that Member States use methodologies agreed upon by the Convention on Long-range

Transboundary Air Pollution (CLRTAP), and requests Member States to use the joint EMEP/CORINAIR

guidebook in preparing inventories and projections.

In addition, the related report ‘Recommendations on developing and reporting national programmes under

the NECD’5 (CAFÉ working group, 2006) also refers to the use of the EMEP guidebook.

The UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP)

CLRTAP was created as a platform for international action against pollution which had the potential to cross

political borders and have effects in countries other than the point of emission. Under CLRTAP a number of

protocols have been added to the Convention dealing with different issues. In the case of air quality and

long range transport of acidifying substances the Gothenburg Protocol (1999) sets down the agreement of

the ratified nations for action against sulphur emissions.

Under Article 1 of the 1999 Gothenburg Protocol, sulphur emissions are defined as:

"Sulphur" means all sulphur compounds, expressed as sulphur dioxide (SO2);”

5 http://ec.europa.eu/environment/archives/air/pdf/recs_national_programmes.pdf

http://ec.europa.eu/environment/archives/air/pdf/recs_national_programmes.pdf



This interpretation of sulphur would include not only sulphur dioxide, but also sulphur trioxide (SO3) and all

other potential forms of sulphur which could be emitted to air. This would also include reduced sulphur (S).

The Gothenburg Protocol was further updated in 2012 to incorporate additional details. In both the 1999

version and 2012 version the definition of ‘sulphur’ under Article 1 remains. However in other aspects of the

Protocol the text is less clear. With sulphur and sulphur dioxide used at different points within the text of the

Convention.

Under the Parties the Convention notes that the bilateral agreements between Canada and the USA relate to

sulphur dioxide only. Additionally under Article 7 for reporting the Protocol states:

“Each Party within the geographical scope of EMEP shall report to EMEP through the Executive

Secretary of the Commission the following information for the emissions of sulphur dioxide, nitrogen

oxides, ammonia, volatile organic compounds and particulate matter on the basis of guidelines

prepared by the Steering Body of EMEP and adopted by the Executive Body”

Although in this case based on the Article 1 definitions ‘sulphur dioxide’ could be interpreted by parties to

include all forms of sulphur expressed as sulphur dioxide. The 2012 Gothenburg Protocol also includes the

emission limit targets of the NECD under Annex II, again expressed as sulphur dioxide only.

Furthermore, Annex V of the 2012 Gothenburg Protocol made certain specific changes to the use of the

terms SOX and SO2. Under the 1998 Protocol Annex IV (Annex V in the revised 2012 Protocol) frequently

refers to SOX (such as at the header of Table 1). Under the 2012 Gothenburg Protocol the same table has

been amended to refer to SO2 only. Additionally, in monitoring compliance the following text has been

added:

For the purpose of this section “emission limit value” (ELV) means the quantity of SO2 (or sulphur

oxides (SOX) where mentioned as such) contained in the waste gases from an installation that is not

to be exceeded. Unless otherwise specified, it shall be calculated in terms of mass of SO2 (SOX,

expressed as SO2) per volume of the waste gases (expressed as mg/m3), assuming standard

conditions for temperature and pressure for dry gas (volume at 273.15 K, 101.3 kPa).

Based on the Article 1 definition under the Gothenburg Protocol it can be assumed that ‘Sulphur’ means all

forms of sulphur emitted to air, however this is to be reported as equivalent to sulphur dioxide. Where

emission factor guidance or major references quote sulphur dioxide only, or SOX and SO2 interchangeably it

does highlight a potential gap in the reporting requirements under CLRTAP, and also the possibility for the

creation of comparability issues between inventories from different reporting nations. However, the most

recent amendments to the Gothenburg Protocol, in particular in relation to Annex V tends to suggest a

recognition that SO2 is considered as the primary pollutant of concern under the general heading of SOX.

The latest UNECE emissions guidance6 refers inventory compilers to the EMEP/EEA guidebook as the major

reference to assist in inventory compilation.

The EMEP Air Pollutant Inventory Guidebook

The latest version of the EMEP Guidebook is the EMEP/EEA Air Pollutant Inventory Guidebook 20137

(hereafter ‘the guidebook’, previously referred to as the EMEP/CORINAIR guidebook). The introduction of

the guidebook includes a section on reporting requirements within the European Union, where it makes clear

that under the NECD Member States are expected to report on sulphur dioxide (SO2), and that the EU 2013

Mechanism for Monitoring and Reporting Greenhouse Gas Emissions also refers to SO2. The Mechanism for

Monitoring and Reporting Greenhouse Gas Emissions is out of alignment with the UNFCCC which requires

reporting of sulphur oxides. The IPPC Guidelines also refer inventory compilers to the EMEP/CORINAR

guidebook.

6 http://www.unece.org/environmental-policy/conventions/envlrtapwelcome/guidance-documents-and-other-methodological-materials/emissions-reporting.html 7 EMEP/EEA air pollutant inventory guidebook 2013. Technical guidance to prepare national emission inventories http://www.eea.europa.eu/publications/emep-eea-guidebook-2013

http://www.eea.europa.eu/publications/emep-eea-guidebook-2013



In the ‘History’ section of EMEP guidebook introduction, the definitions are less clear, whereby it is clear that

CORINAIR always refers to SO2, while the EMEP and TFEIP refer to SOX.

Emission factors quoted within the EMEP/CORINAIR guidebook should be reported on the basis of sulphur

oxides (SOX), although in alignment to the Gothenburg Protocol this can be all forms of sulphur reported as

equivalent to sulphur dioxide (SO2). The emission factors within the EMEP/EEA guidebook quote emission

factors as SOX and SO2 inconsistently between different tables.

In the Energy Industries chapter of the guidebook (Chapter 1.A.1), emission factors for two key sub-sectors

are expressed in SOX (public electricity and heat production and petroleum refining), the guidance states

that the majority of SOX is sulphur dioxide, although a small proportion of sulphur trioxide (SO3) can arise.

The third remaining sub-sector covered by this chapter, manufacture of solid fuels and other energy

industries, states that sulphur oxides (SO2) are generated from residual H2S which has not been removed

from combustion of coke oven gas.

Additionally it is noted that the NECD is currently under review. The ‘proposal for a directive on the reduction

of national emissions of certain atmospheric pollutants and amending Directive 2003/35/EC’8 states there is

a need to revise the NECD in order to a) address significant remaining risks from emissions, and b) align

with the Gothenburg Protocol following a change in the Gothenburg protocol in 2012, albeit that this relates

primarily to the revised ceilings set in the 2012 Protocol.

The proposal is to keep the emissions ceilings set in the NECD for 2010 until 2020, and to introduce new

national emission reduction commitments applicable from 2020 to 2030. These emissions ceilings continue

to refer to SO2, as the NECD does at present.

The United Nations Framework Convention on Climate Change (UNFCCC) and Kyoto Protocol

The UNFCCC Kyoto Protocol (1998) aims to curb the emission of greenhouse gases responsible for global

warming. This gives particular mention to the potent greenhouse gas sulphur hexafluoride. However in

placing reporting requirements on ratified Parties it also discusses indirect greenhouse gases which include

other forms of sulphur. In this case the UNFCCC defines sulphur as sulphur oxides which should be included

within emission inventory reporting. This is in contrast to the EU Mechanism for Monitoring and Reporting of

Greenhouse Gas Emissions which require reporting of sulphur dioxide only.

The CRF reporter used by ratified Parties to provide data under the Convention, including the CRF tables

are labelled as ‘sulphur dioxide’ which is in contrast to the reporting requirement. The International Panel on

Climate Change (IPCC) reporting guidelines used to aid the development of greenhouse gas emission

inventories refer to sulphur oxides and sulphur dioxide interchangeably.

The International Convention for the Prevention of Pollution from Ships, MARPOL9 Annex VI

The International Maritime Organisation’s International Convention for the Prevention of Pollution from Ships

aims to reduce emissions of SOX10 (and NOX, and particulate matter) from ships. MARPOL specifies that

SOX emissions are to be controlled by limiting the sulphur content of fuel (primary compliance method).

However, emission control through the use of exhaust gas treatment systems e.g. scrubbers (secondary

compliance method) to de-sulphurise exhaust gas and reduce SOX emissions is also permitted, so long as it

is ‘at least as effective’ in terms of emission reductions as the prescribed sulphur limits for fuel. MARPOL

regulation sets limits on the sulphur content of fuel, rather than setting limits on the SOX or SO2 emissions

from ships.

MARPOL refers to emissions of ‘SOX’ throughout the regulation, and to sulphur content of fuel. However

where secondary compliance methods are used, the IMO guidelines11 specifies that compliance should be

demonstrated on the basis of the SO2 (ppm) / CO2 (%v/v) ratio values in emissions, therefore relying on the

measurement of SO2 emissions to ensure compliance.

8 Brussels, 18.12.2013 COM(2013) 920 final/ 2013/0443 (COD) 9 MARPOL is short for marine pollution 10 The sulphur content limit for fuels varies depending on whether ships are in or out of an Emission Control Area. 11 IMO Guidelines MEPC 184(59) and MEPC 259(68)



Additional EU policies and legislation

The Ambient Air Quality Directive (AAQD)

Directive 2008/50/EC on ambient air quality and cleaner air for Europe12 (henceforth AAQD) covers

pollutants including: sulphur dioxide, nitrogen dioxide and oxides of nitrogen, carbon monoxide, benzene,

PM and lead, ozone and related NO and NO2.

The AAQD refers to ambient concentrations of sulphur dioxide (SO2) (See Chapter II, Section 1, Article 5).

The AAQD requires real-time ‘live’ measurement of ambient pollutant levels (in Article 7, Sampling points).

The location of sampling points for measurement of SO2 and other pollutants will be determined using criteria

listed in Annex III. One of the aims of the sampling is to ensure pollutant levels in population centres/areas

frequented by large numbers of people are recorded (to ensure protection of human health). However,

measurement in rural backgrounds is also included, to ensure information on background levels is included.

This monitoring data potentially represents a viable source for the development of emissions estimation.

The AAQD refers throughout to SO2, rather than SOX.

Industrial Emissions Directive

The Industrial Emissions Directive13 (IED), includes emissions of sulphur dioxide, SO2 (Chapter III, Article 30

(2) and (3)). In Annex V, Part 5, the directive sets targets as minimum rates of desulphurisation. Annex VI

(related to Chapter IV of the IED), Part 3, sets SO2 emissions limits for waste incineration plants and co-

incineration plants. Chapter II of the IED, that is broader in scope than both chapters III and IV however,

includes a reference to Annex II ‘List of polluting substances’ that includes sulphur dioxide and other sulphur

compounds.

Best Available Technology (BREF) on monitoring of emissions from IED installations

The Reference document (REF) on monitoring emissions from IED installations14, produced by the EU Joint

Research Centre, sets out monitoring guidance for emissions to air from industrial sources.

The REF specifically excludes from its scope ‘detailed information on monitoring methods’, which the BREF

states is covered by CEN. Also, industry-specific aspects will be covered by sectoral BAT Reference

documents (BREFs).

The REF Annexes include EN standards for the measurement of emissions to air, and these provide the

specifications for monitoring techniques. The EN 14791 (the reference method for SO2) measures sulphate

concentration following absorption of SO2 and any SO3 in hydrogen peroxide solution. This is important

because the EN reference method for stack emissions measures SOX and, in theory, this method is used to

calibrate/verify CEMS/AMS which are installed on stacks and which measure SO2 (usually from infra-red

based analysis). So if a CEMS’ calibration function is derived from comparison with EN 14791 tests it is

calibrated for SOX.

However a little caution is needed because most CEMS are calibrated using methods with demonstrated

equivalence to the EN reference method – generally another instrument-based system providing continuous

measurement of SO2 by Infra-red or FTIR.

The Kiev Protocol and European Pollutant Release and Transfer Register (E-PRTR) Regulation (EC/166/2006)

The Kiev Protocol of the Aarhus Convention is intended to make pollutant information publically available in

order to foster public engagement and aid in emission reduction. As a ratified member the EU transposes

this Protocol into EU legislation as the European Pollutant Release and Transfer Register (E-PRTR)

12 OJ 152, 11.06.2008, p.1 13 OJ 334, 17.12.2010, p.17 14 JRC Reference Report on Monitoring of emissions from IED installations. JRC, final draft 2013. Available at: http://eippcb.jrc.ec.europa.eu/reference/BREF/ROM_FD_102013_online.pdf last accessed 28.01.2016

http://eippcb.jrc.ec.europa.eu/reference/BREF/ROM_FD_102013_online.pdf



Regulation (EC/166/2006). This regulation requires operators to provide annual data on a list of 91

pollutants covered by Annex II of the regulation against a set of economic activities (Annex I of the

regulation). The regulation is intended to take the reporting required by a range of EU policy and make this

available publically via the E-PRTR website.

Both the Kiev Protocol and the E-PRTR Regulation (Annex II) quote sulphur as ‘SOX/SO2’, suggesting that

SOX and SO2 are treated interchangeably as one and the same thing. It is unclear what proportion of data

reported to the E-PRTR is SO2 and what proportion is SOX (including SO3).

The E-PRTR represents a major reference source for inventory compilers based on reporting from c.33,000

installations across the EU.

Summary

Review of the NECD and the CLRTAP definitions of sulphur make clear a possible issue for compatibility in

how sulphur is defined. While the NECD is clear that sulphur is assumed to mean SO2 only, CLRTAP

includes all forms of sulphur expressed as SO2. However, a number of related pieces of legislation,

particularly IED all refer to SO2 only. In terms of major reference sources which inventory compilers might

use in developing emission estimates there are similar issues. The E-PRTR refers to SOX/SO2

interchangeably and the main reference for CLRTAP, the EMEP/EEA guidebook provides emission factors

as SOX, although different tables mention either SOX or SO2.

Based on the review of policy and major reference sources identified the available data would suggest a

preference towards SO2 in the majority of cases. A number of references do also quote SOX but the

underlying monitoring and compliance data relates back to SO2 also.

This may suggest a data gap for emission estimates compiled for CLRTAP based on the Gothenburg Article

1 definition.



3. Development of non-Sulphur Oxide emission estimates

The literature and policy documents reviewed provide key focus to either SO2 as the dominant source of

sulphur, or ‘SOX’ being the main priority for emissions to air. The guidance from CLRTAP15 comments that

the main emission of sulphur to the atmosphere is through the combustion of fuels which contain sulphur. In

these cases the main pollutant generated from combustion is SO2, while it is also possible to form SO3 from

oxidation of combustion vapours. The Article 1 definition within CLRTAP alludes to ‘all’ forms of sulphur

emitted to air expressed as sulphur dioxide. This recognises that it is possible to generate non-oxide forms

of sulphur which once released to the atmosphere are subsequently converted to SO2 or SO3 through

oxidation.

These non-oxide forms of sulphur may therefore represent an important part of the overall sulphur emission,

and are worth considering during inventory compilation. To assess the nature and occurrence of the non-

oxide forms of sulphur a review has been conducted to identify which species and sources are likely to be

relevant. Based on this review the following reduced sulphur compounds are discussed in this chapter:

Hydrogen sulphide - H2S

Methyl mercaptan - CH3SH

Dimethyl sulphide - C2H6S

Dimethyl disulphide - (CH3S)2

Carbon disulphide - CS2

Carbonyl sulphide - COS

Sulphuric acid 16 - H2SO4

Sulphite/Hydrosulphite/Bisulphite - SO32- / HSO3

- / S2O42-

In developing the text for these species we would also like to acknowledge the support of Kristina Saarinen

at SYKE, Finland, who has provided guidance and technical contributions during the development of the text.

Hydrogen Sulphide (H2S)

Anthropogenic sources (Amec 2004, NPI, 2015)

Hydrogen sulphide can be released during oil and gas extraction. It is also formed in industrial processes

whenever elemental sulphur or sulphur-containing compounds come into contact with organic materials at

high temperatures. Examples include coke production, iron smelters, petroleum refining, natural gas plants,

petrochemical plants, viscose rayon production, textile plants, waste-water treatment plants, wood pulp

production using the sulphate method, sulphur extraction processes, food processing plants, the tanning

industry, manure treatment facilities, landfills and waste water treatment facilities. It can also be released

during geothermal energy production.

Natural sources (Amec, 2004, NPI, 2015)

Natural sources include swamps, bogs, and volcanoes. Annually, 100–324 million tons of hydrogen sulphide

are released from natural sources with half from volcanoes, flooded ground, or hydrogeological sources, and

15 UNECE, 2015, ‘Guidance document on control techniques for emissions of sulphur, nitrogen oxides, volatile organic compounds and particulate matter (including PM10, PM2.5 and black carbon) from stationary sources’ 16 S is not in a reduced state in H2SO4, but it is included here because it may not be captured by some SO2 measurement techniques.



the other half from the oceans. 90% of the total global emissions of this compound are estimated to be of

natural origin.

Methyl Mercaptan (CH3SH)

Anthropogenic sources (Amec, 2004)

Methyl mercaptan may be released as fugitive emissions and in wastewater during its production or use in

the manufacture of methionine, jet fuels, fungicides, pesticides, and plastics. It is released to the

environment in emissions from starch manufacturing, petroleum refining, shale oil production, rendering

plants and the cooking of animal and vegetable food. It is present in non-condensable gases in the pulp and

paper industry, with the primary sources in a Kraft mill being digesters, evaporators and turpentine recovery

systems. West Texas sour gas contains sufficient amounts of methyl mercaptan that commercial quantities

are extracted from it.

Natural sources (Amec, 2004)

Methyl mercaptan can be emitted from vegetation (e.g. saline marsh, vegetables such as garlic and onion),

the putrefaction of proteins, and microbial degredation. Animal wastes are a source, as are livestock

directly, caused by formation in the intestinal tract from the action of anaerobic bacteria on albumin. Some

natural gas reserves are also high in methyl mercaptan, resulting in emissions from gas seepage.

Dimethyl Sulphide (C2H6S)


Dimethyl sulphide is used in petroleum refining to pre-sulphide hydro-desulphurization catalysts and as a

pre-sulphiding agent to control the formation of coke and carbon monoxide in ethylene production; in organic

syntheses; and as a food flavouring component. It can also be oxidized to dimethyl sulphoxide, (DMSO),

which is an important industrial solvent. It is manufactured from hydrocarbon-based feedstocks.


Dimethyl sulphide is the major volatile reduced organic S compound in open ocean, coastal waters and

marshlands. Its emission from surface water represents a major flux of biogenic reduced sulphur to the

atmosphere. It also occurs from decomposition of plants and animals and from sulphur-containing amino

acids during digestion by micro-organisms in the rumen of ruminants. Small quantities also arise from

methyl mercaptan in natural gas.

Dimethyl Disulphide (CH3S)2


Dimethyl disulphide emissions result from fish processing, rendering, sewage treatment, SO2 scrubbing,

starch manufacture, whisky manufacture and wood pulping. It has been detected in the air of refuse waste

from a food centre, and in exhaust gases from pulp mills and gasoline engines. Effluent treatment ponds at

pulp and paper mills emit dimethyl disulphide and other reduced S compounds.


Dimethyl disulphide is released from animal waste, food decay, microbes, natural gas, vegetation, oceans

and soil. Under waterlogged conditions it is formed by microbial degradation of methionine and carbon

disulphide from cysteine and cystine. Plants like oak and pine emit dimethyl disulphide, as well as

actinomycetes.

Carbon Disulphide (CS2)

Anthropogenic sources (Amec, 2004, NPI, 2015)



The most important industrial use of carbon disulphide is in the manufacture of regenerated cellulose rayon

(by the viscose process) and cellophane. Another major use is as a feedstock for carbon tetrachloride

production. It has also been used to protect fresh fruit from insects and fungus during shipping, in adhesives

for food packaging, and in the solvent extraction of growth inhibitors.

Further uses include the vulcanisation and manufacture of rubber and rubber accessories; the production of

resins, xanthates, thiocyanates, plywood adhesives and flotation agents; solvent and spinning-solution

applications, primarily in the manufacture of rayon and polymerisation inhibition of vinyl chloride; conversion

and processing of hydrocarbons; petroleum-well cleaning; brightening of precious metals in electroplating;

rust removal from metals; and removal and recovery of metals and other elements from waste water and

other media. In agriculture, carbon disulphide has been widely used as a fumigant to control insects in

stored grain, and to remove botfly larva infestations from the stomachs of horses and ectoparasites from

swine. Use of carbon disulphide as a grain fumigant in the USA was voluntarily cancelled after 1985.

Natural sources (Amec, 2004, NPI, 2015)

Major sources are seas and oceans. Volcanic emissions also occur, as well as emissions from marshlands.

Terrestrial diurnal variation in emission rates depends on soil temperature and solar irradiation. Emissions

from temperate pine forest are increased nine-fold when nitrogen fertilizers are added.

Carbonyl Sulphide - COS

Anthropogenic sources (Amec, 2004, The Agency for Toxic Substances and Disease Registry, 2015)

Carbonyl sulphide may be released to the environment from the combustion of coal, oil, biomass, waste and

plastics; flue gas desulphurization sludge field storage sites; extraction of natural gas; natural gas liquids

recovery facilities (where it has a tendency to concentrate in the propane and propylene streams); petroleum

manufacture; and manufacture of synthetic fibres, starch and rubber. It may also be formed in the

atmosphere by the gas-phase reaction of carbon disulphide and photochemically produced hydroxyl radicals.

Blake et al. (2004) estimated total carbonyl sulphide emissions from anthropogenic sources from different

countries located in Asia to be 146 Gg/year. The main sources were coal, oil, biomass and biofuel

combustion, industrial production and agriculture (mainly rice paddies). In the USA, the USEPA estimated

releases of approximately 6,000 tonnes of carbonyl sulphide to the atmosphere from over 100 manufacturing

and processing facilities in 2011, accounting for about 99% of the estimated total environmental releases

from the large plant required to report to the Toxics Release Inventory.

Natural sources (Amec, 2004, The Agency for Toxic Substances and Disease Registry, 2015)

Emissions occur from oceans, salt marshes, inland swamps, soil plants, burning of biomass, volcanoes and

fumaroles. Emissions also occur from deciduous and coniferous trees.

Sulphuric Acid - H2SO4

Anthropogenic sources

Sulphuric acid is one of the large volume industrial chemicals, used mainly in the production of phosphate

fertilizers, explosives, other acids, dyes, glue, wood preservatives and automobile batteries. It is also used

in the purification of petroleum, the pickling of metal, copper smelting, electroplating, metal work, and the

production of rayon and film.

Natural sources

No information has been obtained on natural sources.

Sulphite/Hydrosulphite/Bisulphite

Anthropogenic sources

It is thought that emissions to air arise from sulphuric acid leaks, textile dyes and waste treatment. But more

work is needed to confirm this.



3.1 Sources Expected to Emit Reduced Sulphur Compounds

Most of the reference material for this section comes from Australia where reduced sulphur compounds are

included in the reporting of emissions to air. European reporting does not include emissions of individual

reduced sulphur compounds.

Fossil Fuel Extraction

Oil Sand Plant

Sulphur compounds are released during the extraction and processing of oil sands, and whilst this will be

dominated by S in an oxidised state, some emissions of reduced S will also occur. Emissions depend on the

sulphur content of the oil and the degree of sulphur recovery. For example, emissions from the oil sands

industry in Canada fell by 26% from 2009 to 2013 due to a higher proportion of production from in-situ

recovery rather than oil sands mining, plus greater use of sulphur recovery technology. However, emissions

are expected to increase in future years due to the increasing sulphur content of oil sands and higher

absolute production levels (CAPP, 2015).

Reduced sulphur compounds will be emitted from fugitive sources, such as the mine facings, the tailings

ponds, and via valve/fittings leaks in the bitumen processing area. The main source of hydrogen sulphide is

from tailing ponds. There are also small amounts emitted from produced gas (i.e. co-produced with the oil)

that is used in steam boilers / generators and heaters.

Oil and Gas Extraction

Petroleum and natural gas with a high content of hydrogen sulphide is considered ‘sour’. Usually hydrogen

sulphide is present at just a few parts per million, but sometimes this can rise to over 20%. Exposure to

concentrations above 1000ppm can be fatal to humans (Skrtic, 2006). Fugitive emissions of hydrogen

sulphide may originate at wellheads, pumps, piping, separation devices, oil storage tanks, water storage

vessels, and during venting and flaring (to burn gases that cannot be sold or as a safety measure where

operating problems may occur) (NPI, 2015). During flaring, hydrogen sulphide is mainly converted into

sulphur dioxide but some may be emitted if there is incomplete combustion. The USEPA (1993) has

documented cases of sour gas well blowouts, line releases, extinguished flares, collection of sour gas in low-

lying areas, and leakage from idle or abandoned wells that have impacted the public near oil and gas

extraction sites. If a well is improperly sealed, hydrogen sulphide may routinely seep into the atmosphere.

Manufacture of Fuels

Refineries

Hydrogen sulphide is a by-product in the purification of natural gas and refining of crude oil, including natural

gas sweetening and sulphur removal plants. Potential accidental sources include flares (vapour incinerators,

heater-treaters (an oil/water/gas separation device), storage tanks and equipment (valves, flanges, etc.).

Coke Ovens in Iron and Steel Manufacture

Hydrogen sulphide emissions can come from the coking gas purification process and from slag granulation.

Potential sources of reduced sulphur compounds in the iron and steel industry are:

Iron slag quenching operations;

Coke oven and by-products plant;

Coke quenching; and

Quenching of steel slag. This is possible at low levels: steel slag has 0.05% S, iron slag has

1.5% S (Cocchiarella 1994).



Hydrogen sulphide is generated at a rate of 50–80 g/t of coke (World Bank, 1998)

Industrial Processes and Product Manufacture

Information has been obtained on sources of reduced sulphur compounds from industrial sources, but further

work is required to analyse and process the information in any detail (particularly for the chemical industry).

The Chemical Industry and Product Manufacture

Emissions from sulphuric acid plants include S compounds that have not been oxidized to sulphur dioxide,

and compounds not absorbed by abatement equipment such as sulphur trioxide and hydrogen sulphide

(NPI, 2015).

Hydrogen sulphide containing gases are cleaned in a scrubber and the washing liquid is returned into the

process. Hydrogen sulphide emissions can be 2 - 3 kg S (as SO2) per tonne of H2SO4 manufactured.

During exceptional situations, such as malfunctioning abatement equipment, the emissions are typically 3-5

fold (NPI, 2015).

Emissions also arise from fertiliser manufacture (NPI, 2015), the manufacture of polymers, the manufacture

of cleaning compounds and toiletries (NPI, 2015), pine oil manufacture and mineral wool manufacture.

Reduced S compounds are also emitted from product manufacture, such as electrical equipment (NPI,

2015), motor vehicles and motor vehicle parts manufacture (NPI, 2015).

Food Processing

Sulphur dioxide is widely used in the food and drinks industries for its properties as a preservative and

antioxidant, preventing bacterial growth and the browning of fruit. Sodium hydroxide and sulphuric acid are

used as detergents (see also Food Waste below). It has also been shown that the use of barbecues can

result in the emission of sulphuric acid (NPI, 2015).

Metal Industry and Ore Mining

Basic ferrous metal processing can result in the release of sulphuric acid and hydrogen sulphide (NPI, 2015,

Komulainen et al, 2014). Basic non-ferrous metal processing can result in the release of hydrogen sulphide

and sulphuric acid (NPI, 2015, Komulainen et al, 2014). Metal ore mining can result in the emission of

sulphuric acid, hydrogen sulphide and carbonyl sulphide (NPI, 2015).

Pulp and Paper Industry

Reduced S compounds can contribute more than 50% of the total annual S emissions at old or not well

managed paper manufacturing plant. Reduced sulphur compounds characteristic of kraft pulping are

malodorous at extremely low concentrations and are generally destroyed or collected rather than being

released to the air. Typical compounds include hydrogen sulphide, methyl mercaptan, dimethyl sulphide and

dimethyl disulphide.

Malodorous gases can be captured, but this is not easily achieved with diffuse emissions. Emissions can

also arise during periods of abatement technology breakdown.

In Finland S emissions (both SO2 and reduced S compounds) have been reduced by 80% due to primary

measures (using lower sulphur content wood, increasing the dry content of black liquor), and secondary

measures (the introduction of a S scrubber removes 90% of flue gas SO2, and collecting and incinerating

malodorous gases has been introduced). Reduced S compounds comprised approximately 25% of total SO2

at the beginning of the 1990’s. However the contribution in recent years is approximately 10%.

An unabated plant generates 2-6 kg of reduced S compounds per tonne of air dried pulp (before 1990,

emissions were an order of magnitude higher). A modern plant with abatement equipment generates around

0.4 kg S/tonne of air dried pulp. An SO2 scrubber removes about 99% of sulphur (both reduced S and SO2),



and the remaining reduced S compounds are burned in a dedicated incinerator. However it is not possible to

easily abate fugitive emissions.

Reduced S compounds are generated in all partial processes of a pulp mill. The sulphur gases are divided

into low and high concentration gases based on the thresholds for explosiveness:

High Volume Low Concentration Gases – low reduced S content.

Low Volume High Concentration Gases and Concentrated Non-Condensible Gases –up to 60%

reduced S content.

Malodorous sulphur gases need to be collected from non-condensible gas streams from across the pulp mill.

The gases can be treated with the sulphur scrubber and incinerated in specific TRS incinerators.

Diffuse TRS emissions consist mainly of low concentration gases, the concentration of which is kept low by

mixing with secondary and tertiary air and leading the gases into the recovery boiler. 85-97% of malodorous

gases can be collected, thus diffuse emissions of reduced S compounds may contribute around 80% of total

S emissions.

Figure 3.1 below shows total emissions of sulphur compounds from European pulp and paper mills that

responded to a 2011 questionnaire, showing a very wide variation in emissions depending on the degree of

abatement technology. Note that in Europe exceptional sulphur emissions e.g. during malfunctioning of

abatement technique or under process failure are generally not included in reporting by the plants (BAT

Monitoring TWG information) and so are not included in emission inventories, as the EFs used in top-down

inventories do not take into account exceptional situations, and few countries use data reported by the plants

in their inventories.



Figure 3.1 Total S emission load (as kg S/tonne of air dried pulp) from major processes (recovery boiler, lime kiln, NCG burner) including uncollected or untreated weak gases (European Commission, 2015)

The pulp and paper industry also produces emissions of sulphuric acid. In Australia emissions for 2013/4

were estimated as 13 tonnes (NPI, 2015).

Textile industry

Viscose and Rayon Production

Hydrogen sulphide and carbon disulphide are used as chemicals in the production of viscose and rayon.

The production of viscose generates emissions to air in the form of sulphur, nitrous oxides, carbon

disulphide, hydrogen sulphide and carbonyl sulphide.

Emissions are collected, passed through a scrubber and incinerated. However, small amounts of hydrogen

sulphide may be emitted into the air.

Silk Production and Processing

The accidental release or improper disposal of materials resulting from these processes may result in

hydrogen sulphide emissions.

Wool scouring & Carbonising

Wool scouring and carbonising can result in the emission of sulphuric acid (NPI, 2015).



Tanneries

Leather tanning, fur dressing and leather product manufacturing can result in the emission of sulphuric acid

(NPI, 2015).

Other Industrial Process Sources

Other industrial processes which can result in emissions include:

Ceramic products - production of bricks can result in sulphuric acid emissions (NPI Australia

19).

Rubber vulcanisation - the accidental release or improper disposal of materials may result in

hydrogen sulphide emissions.

Wood bonding - Some wood bonding involves pre-treatment with bisulphite.

Storage tanks, such as bisulphite storage tanks at de-chlorination plants can result in

emissions.

Lithography and photoengraving - accidental release or improper disposal of materials

resulting from these processes may result in hydrogen sulphide emissions.

Agriculture

Animal Feedlots

Hydrogen sulphide and other reduced sulphur compounds are produced as manure decomposes

anaerobically. There are two primary sources of sulphur in animal manures. One is the sulphur amino acids

contained in the feed. The other is inorganic sulphur compounds, such as copper sulphate and zinc

sulphate, which are used as feed additives to supply trace minerals. Sulphates are used in all sectors of

animal agriculture but most extensively in the poultry and swine industries. Trace minerals in drinking water

may also be a significant source of sulphur.

Reduced sulphur can be emitted as hydrogen sulphide, methyl mercaptan, dimethyl sulphide, dimethyl

disulphide, and carbonyl sulphide. Small quantities of other reduced sulphur compounds are likely to be

emitted as well. Under anaerobic conditions, all excreted sulphur will tend to reduce microbially to hydrogen

sulphide, making this the predominant form of reduced sulphur (USEPA, 2001).

A study on 2 anaerobic lagoons used for treating swine waste showed a mean hydrogen sulphide release of

180 g m-2 year-1 (Lim et al. 2003). Further studies on hydrogen sulphide emissions from anaerobic lagoons

include Park et.al. (2014) and Beghi et.al. (2012).

Aerobic conditions generally prevent reduced sulphur compounds from forming, although it is very rare for

animal manure to be entirely aerobic.

Waste

Waste Treatment and Landfills

Waste treatment, disposal and remediation services can result in the release of sulphuric acid and hydrogen

sulphide (NPI, 2015), and landfill can result in the emission of hydrogen sulphide (NPI, 2015, The Agency for

Toxic Substances and Disease Registry 2000).

Food Waste

Food wastes emit volatile organic sulphur compounds (VOSCs). VOSC include dimethyl disulphide (DMDS),

dimethyl sulphide (DMS), methyl 2-propenyl disulphide, carbonyl sulphide and methyl 1-propenyl sulphide

(with shares of 75.5%, 13.5%, 4.8%, 2.2% and 1.3% in total 15 VOSCs released, respectively).



Emission have been estimated to be approximately 410 mg per kg dry weight of food waste.

Production of VOSC species is induced mainly by microbial activities during the aerobic decomposition.

Released VOSCs may account for 5.3% of sulphur content in the food wastes, implying that during aerobic

decomposition considerable portion of sulphur in food wastes would be released into the atmosphere as

VOSCs, primarily as DMDS, which is very short-lived in the atmosphere and thus usually less considered in

the sources and sinks of reduced sulphur gases (Wang X et al, 2010).

Slaughterhouses

Reduced S compounds also arise from by-products and waste. For instance, the heat treatment of protein

will lead to the formation of a number of malodorous compounds. Releases of VOSC include H2S,

mercaptans and a number of organic disulphides (EIPPCB, 2005, NPI, 2015). These compounds can be

found in the non-condensable gases from hydrolysis and drying. Odour gases are emitted through

ventilation if not collected and incinerated. A flare can be used to prevent odours.

Wastewater Treatment

Hydrogen sulphide can be emitted by sewerage, water supply and drainage processes (NPI, 2015).

Treatment of Contaminated Soil

The treatment of contaminated soil can result in the emission of sulphur compounds such as hydrogen

sulphide, methyl mercaptan, dimethyl sulphide and dimethyl disulphide.



4. Comparison of SO2 vs SOX emissions

4.1 Introduction

The major contributors to global acidification are sulphur oxides and nitrogen oxides, which are emitted

mostly by the burning of fossil fuels. From a scientific viewpoint, it is important to make a clear distinction

between sulphur dioxide (SO2) and sulphur trioxide (SO3) when referring to sulphur oxide (SOX) emissions,

as both pollutants have different properties. SO3 has a toxicity over ten times that of SO2 and is highly

corrosive, meaning that it can have a more pronounced effect on local human health. An important initiative

at the third European conference of environment ministers was that the issue of human health related to

local air pollution should be given priority over that of global air pollution. While the reduction in emissions of

sulphur dioxide and nitrogen oxides have mainly been effective at reducing acidification due to long-range

transport, the reduction of sulphur trioxide may be more effective at improving local human health (Kikuchi,

2001).

The first section of this chapter provides an overview of the top ten sources of sulphur oxide (SOX)

emissions under the National Emission Ceilings Directive (NECD) and the Convention on Long-range

Transboundary Air Pollution (CLRTAP). A review of the ratios of SO2, SO3 and other S compounds for these

key sources of SOX emissions is provided in the next section, followed by a short study on the effects that

different abatement techniques can have on the ratios of sulphur compounds.

4.2 Review of key emission sources for SO2 and SOX

Table 4.1 shows reporting of SOX and SO2 for the year 2013 from EU28 countries for the 12 highest emitting

sectors. While the main sources of emissions are broadly the same for LRTAP (SOX) and NECD (SO2)

reporting, there are some differences in reported emissions and in the relative contribution of the sector, as

highlighted in the table.

The most notable differences for reported emissions are for 1A3di(i) International maritime navigation,

1A2gviii Stationary combustion: Other and 1A2f Stationary combustion: Non-metallic minerals.

Table 4.1 A list of the 12 highest emitting sectors under the National Emission Ceilings Directive (NCED) and the Convention on Long-range Transboundary Air Pollution (CLRTAP) for 2013.

LRTAP, SOX NECD, SO2

NFR

Code

Sector name Emissions -

Gg (1000

tonnes)

NFR

Code


Gg (1000

tonnes)

1A1a Public electricity and heat

production

1,562 1A1a Public electricity and heat

production

1,566

1A3di(i) International maritime navigation 1,131 11A Volcanoes 943

11A Volcanoes 943 1A3di(i) International maritime navigation 559

1A4bi Residential: Stationary 417 1A4bi Residential: Stationary 419

1A1b Petroleum refining 197 1A2gviii Stationary combustion in

manufacturing industries and

construction: Other

214

1A2gviii Stationary combustion in


construction: Other

143 1A1b Petroleum refining 200

1A2a Stationary combustion in


construction: Iron and steel

141 1A2a Stationary combustion in


construction: Iron and steel

140

1A2f Stationary combustion in


construction: Non-metallic minerals

141 1B2aiv Fugitive emissions oil: Refining /

storage

92



LRTAP, SOX NECD, SO2

NFR

Code


Gg (1000

tonnes)

NFR

Code


Gg (1000

tonnes)

1B2aiv Fugitive emissions oil: Refining /

storage

102 1A2c Stationary combustion in


construction: Chemicals

92

1A2c Stationary combustion in


construction: Chemicals

92 2B10a Chemical industry: Other 82

2B10a Chemical industry: Other 83 1A2f Stationary combustion in


construction: Non-metallic minerals

81

1A4ai Commercial/institutional: Stationary 73 1A4ai Commercial/institutional: Stationary 74

Source: EEA, (2015)

Table 4.2 presents an indication of the main sources for sulphur emissions within each sector. As indicated

there are common sources across a number of sectors.

Table 4.2 Main emission sources within the highest emitting sectors

Sector Main emission sources

1A4bi Residential: Stationary Coal and oil fired boilers, stoves and fireplaces

1A1a Public electricity and heat production Coal and oil fired boilers and generators (or cogeneration)

1A2gviii Stationary combustion in manufacturing industries and construction: Other

1A2f Stationary combustion in manufacturing industries and construction: Non-metallic minerals

1A4ai Commercial/institutional: Stationary

1A1b Petroleum refining Coal and oil fired boilers and generators (or cogeneration), and combustion of unconventional fuels (by product/ waste liquids and gases)

1A2c Stationary combustion in manufacturing industries and construction: Chemicals

1B2aiv Fugitive emissions oil: Refining / storage Fugitive and process emissions - varied sources

2B10a Chemical industry: Other

1A2a Stationary combustion in manufacturing industries and construction: Iron and steel

Coal and oil fired boilers and generators (or cogeneration), and coke ovens, sinter plant, blast furnace, coke oven gas (COG) fired boilers

1A3di(i) International maritime navigation Oil fired engines

11A Volcanoes Natural source

4.3 Ratios of sulphur compounds in SOX

Industrial production processes account for a considerable share of the overall pollution in Europe due to the

sulphur emissions of air pollutants, discharges of wastewater and the generation of waste. While



combustion sources dominate the sulphur emissions to air, particularly large point sources, non-combustion

processes still account for an important proportion of the total emissions. The major sources of sulphur

emissions from non-combustion sources under the LRTAP and NECD are: refineries & storage, iron & steel

and chemical installations. While industry bodies responsible for these non-combustion sources report their

SO2 emissions under the Industrial Emissions Directive (Directive 2010/75/EU), the main EU instrument

regulating pollutant emissions from industrial installations, they fail to provide information on the ratios of

SO2:SO3 emissions. A thorough review of the information reported on non-combustion emissions has

identified a need for greater need for clarity in relation to the different forms of sulphur and the proportion of

non SO2 compounds that make up the total sulphur emissions.

The remainder of this chapter therefore provides an overview of the key issues for emissions of sulphur to air

relating to combustion sources only.

Chemistry

Emissions of sulphur oxides are mainly a result of the presence of sulphur in fossil fuels. In scientific

literature, varying and sometimes conflicting estimates exist regarding the conversion of SO2 to SO3. For

example, in one publication the conversion rate is estimated to vary from 3 to 5 percent, from 1.25 to 5

percent, and from 1 to 4 percent, depending on the section of the book being read (Singer, 1991). Broadly

though, sulphur in fossil fuels is converted to sulphur dioxide (typically at least 95%), with a small percentage

(a maximum of 5%) of the sulphur dioxide formed being oxidised into sulphur trioxides (SO3) by a two-step

reaction:

(1) S + O2 > SO2

(2) SO2 + ½ O2 > SO3

The remainder is converted to sulphate particulates. The SO3 concentration might be negligible in a small

combustion unit, but it increases as the temperature of the fire chamber rises and the excess air factor (ratio

of supply air to theoretical stoichiometric amount of air in combustion) increases in a larger unit. SO3

concentration increases considerably at 800°C or higher, and reaches a maximum at around 1600°C

(Kikuchi, 2001).

Figure 4.1 SO3/SOX ratio for different oxygen to fuel ratios (Flegg et al. 2013)



Ratio of sulphur compounds in SOX

The emission of SO2 is directly dependent on sulphur content of fuel. However, there are also significant

variations in SO3 emissions from coal fired power stations, depending upon the reference source. While it

has been reported that SO3 concentration rarely exceeds 35 ppmv (Danielson, 1967), concentrations of up

70 ppmv were observed at a brown-coal fired power plant in the Czech Republic and 140 ppmv at a

Slovenian thermal power plant (Kikuchi, 1997), as well as concentration of up to 240 ppmv reported at a

lignite-fired power plant in Bulgaria (Pelovski, 1996; Kikuchi, 2001). For coals, the content of the calcium

carbonate is relevant due to its chemisorbtion of generated SO2, meaning that coal types with a calcium rich

ash tend to have the lowest SO3/SOX ratio in the flue stack (Kubica et al. 2007). It is therefore clear that for

the combustion of coal, the grade of the coal being burned impacts the rate of conversion from SO2 to SO3.

There are also numerous design and operating parameters that influence the amount of SO3 formation in a

power plant. Among these are fuel sulphur content, excess air level, ash content and composition,

convective pass surface area, and gas and tube surface temperature distributions.

Table 4.3 provides an overview of ratios for sulphur compounds in SOX, from the highest sulphur emitting

sources for which evidence has been identified in this review. Data was retrieved from several different

sources. While the USEPA AP-42 compilation of air pollutant emission factors was used as a primary source

of information, specific information on the ratios of sulphur compounds were only available for a limited

number of sectors. The other primary source used to generate sector specific information were Best

Available Techniques (BAT) reference documents (BREFs) from the European Commission. Where these

two sources failed to yield sufficient information, a broader internet search was conducted to fill in any gaps

in the reporting.

Table 4.3 Ratios of SO2, SO3 and other S compounds for high emitting sectors

NFR Description Fuel SO2 % SO3 % Other S %

Source

1A1a* Public electricity and heat production Coal, Lignite, Biomass, Peat, Oil

95 3-4 - (European Commission, 2006)

1A3dii International maritime navigation Oil 95-97 3-5 - (Andersen, 2012)

1A4bi** Residential: Stationary Coal/ Oil >95 1-5 1-3 (USEPA, 1995; Kubica et al. 2007)

1A2gviii*** Stationary combustion in manufacturing industries and construction: Other

Coal/ Oil >95 1-5 1-3

1A2f*** Stationary combustion in manufacturing industries and construction: Non-metallic minerals

Coal/ Oil >95 1-5 1-3 (Bamford & Tipper, 1972)

1A4ai*** Commercial/institutional: Stationary Coal/ Oil >95 1-5 1-3

‘ * ‘ - Covers, in general, combustion installations with a rated thermal input exceeding 50 MW, including the power industry and those industries where ‘conventional’ (commercially available and specified) fuels are used. Coal, lignite, biomass, peat, liquid and gaseous fuels (including hydrogen and biogas) are regarded as conventional fuels

‘ ** ’ - Covers boilers with indicative capacity between 50 kW and 50 MW used in multiresidential houses, block of flats and small to medium sources in the commercial and institutional sector. This includes boilers include solid manually fuel boilers, typically with capacity up to 1 MW. It also includes automatic feed boilers, such as moving bed combustions, fuel oil combination boilers (watertube, firetube castiron and tubeless boiler designs) and CHP with maximum capacities of 1.5 MW up to 50 MW.

‘ *** ‘ - Data inferred from 1A4bi, as combustion industries and commercial/industrial (stationary) are expected operate on Coal/Oil fired boilers, similar to the emission sources in Residential Stationary. Combustion units will predominantly be smaller than those in 1A1a.

‘ – ‘ - No reliable sources of information could be found regarding the ratios of sulphur compounds.



The majority of SOX is emitted as SO2, typically at least 95%. While there is variation in the production of

SO3, there are no examples of SO3 concentrations found to be above 5% of the total volume of sulphur

compounds. SO3 concentrations are therefore not considered to be large enough to make a difference in the

compatibility of the emissions estimating between different sectors.

Shortcomings in sector specific information has meant that information relating to the ratios of sulphur

compounds within SOX could not be found for all of the highest emitting sources, namely petroleum refining,

chemicals and iron and steel sectors. Within these sectors a significant proportion of sulphur emissions arise

from conventional combustion for which contribution of SO2 can be assumed to be at least 95%. However,

these sectors also include sulphur emissions arising from combustion of unconventional fuels and sector

specific processes, for which insufficient evidence has been identified to draw a firm conclusion.

4.4 Effect of abatement technologies on ratios of sulphur compounds in SOX

Formation of SO3 and H2SO4

Emissions of sulphur trioxide (SO3) and flyash are the major components of flue gas that contribute to plume

opacity and acid deposition. Estimates are that 75% to 85% of bituminous coal-fired plants with selective

catalytic reduction (SCR) and/or wet flue gas desulfurization (FGD) systems are likely to produce enough

SO3 vapour and mist to make their emissions opaque. Plants fuelled by subbituminous coal and lignite do

not have the same problem The impact of SCR-related SO3 emissions for subbitumous and lignite plants is

assumed to be negligible as a result of SO3 absorption by their alkaline rich flyash (Murphy, 2007). SO3

related stack opacity problems, including the phenomenon known as ‘blue plume’ will become more

prevalent as more coal plants are retrofitted with pollution abatement technologies to meet increasingly lower

sulphur dioxide (SO2) and nitrogen oxide (NOX) emissions limits. In coal fired power plants, sulphuric acid

(H2SO4) is created in the ductwork downstream of the boiler by the combination of water vapour and SO3

,both of which are produced during the coal combustion process. Virtually all of the SO3 converts to H2SO4

as flue gas is cooled in the air preheater (APH). Relatively high concentrations of SO3/H2SO4 in the boiler,

stack, or plume can cause adverse impacts to plant equipment and to the environment.



Figure 4.2 A schematic diagram of SO3 and H2SO4 being formed in a bituminous coal-fired power plant (Murphy, 2007)

There are three main components of particulate matter (PM) in the flue gas of a coal-fired power plant that

reaches the stack: particles of flyash that make it past the electrostatic precipitator (ESP) or fabric filter (FF),

solids carried over from the wet FGD system, and condensable sulfuric acid (H2SO4) aerosols (Figure 4.2)

(Murphy, 2007).

Formation of SO3 in SCR Reactors

While selective catalytic reduction (SCR) is increasingly being used at power plants to control emissions of

oxides of nitrogen (NOX), a major problem associated with the technology is related to the oxidation of SO2 in

the SCR reactor. The increase in the amount of SO3 produced, is due to the fact that as NOX is reduced to

nitrogen and water by the reaction with ammonia (NH3) in the presence of the catalyst, meaning that a small

fraction of SO2 is oxidized to SO3 (Moser, 2006). Usually 0.2-2% of the SO2 is oxidised to SO3, which can

have various effects on the flue-gas cleaning system, typically increasing deposits and corrosion in the air

pre-heater and gas-gas heat exchanger of power plants. If needed, SO3 emissions can be mitigated using a

variety of methods, covered in more detail later in this chapter (Srivastava, 2004)17.

Flue gas desulphurisation (FGD) and formation of aerosols in wet FGD systems

Flue-gas desulphurisation (FGD) technology is based on a chemical reaction that occurs when sulphur

compounds from the exhaust flue gases of fossil-fuel plants come into contact with limestone (CaCO3). The

effects upon the ratios of sulphur compounds vary depending upon the type of scrubber used, with SO3

being more effectively removed in spray dry scrubbers than in wet scrubbers.

Plants that burn coal with medium to high sulphur content and that are equipped with wet FGD systems are

particularly prone to experiencing sulfuric acid-related stack opacity problems. This is because the gaseous



H2SO4 is condensed to an aerosol mist before the wet FGD system, which cannot remove it as readily as it

can SO2.

Wet lime/limestone scrubbers remove 92-98% of both SO2 and SO3, while dry scrubbers remove 85-92% of

SO2 and 95% of SO3, meaning that the ratio is driven more strongly towards SO2 in the presence of dry

scrubbers. As spray dry scrubbers can remove more SO3 than wet scrubbers, there is likely to be less of a

problem of H2SO4 in the environment close to the plant than with wet scrubbers, as well as reduced

corrosion and fouling on the air preheater and the particulate control device. However, due to wet lime

scrubbers ability to remove a greater amount of SO2 than dry scrubbers and to therefore increase

compliance with regulations, they are used far more ubiquitously. Of the total installed FGD capacity, 80%

are wet scrubbers, of which 72% use limestone as a reagent, 16% use lime and 12% use other reagents

(European Commission, 2013).

Mitigation of SO3 Emissions

Understanding the parameters leading to excessive generation of SO3 and subsequent formation of H2SO4

can assist in selection of practical mitigation approaches. The mitigation of SO3 has been an active area of

research for many years. This research has resulted in the development, refinement, and implementation of

different techniques and methods for the successful mitigation of SO3 in the flue gases of fossil-fuel–fired

boilers. A comprehensive guide that summarizes SO3 mitigation options and their respective success in

either full-scale or pilot testing has been written, some of which have been outlined below (Peterson &

Jones, 1994).

Injection of alkali materials into the furnace, either with the fuel or in slurry form, has resulted in reductions of

up to 80%. Post-furnace injection of alkali materials can achieve up to 90% reductions but can increase

particle loadings and ash resistivity characteristics. NH3 injection can also reduce SO3/H2SO4 by 90% and

may result in increased particle loading to the downstream collection systems. In plants with adequate

operational and equipment flexibility, fuel switching and blending can be used to reduce formation and

emissions of SO3. Wet Electrostatic Precipitators (WESPs) are also an option for control of SO3/ H2SO4,

and a variety of designs have been successfully demonstrated for collection of acid mists and opacity control

(Peterson & Jones, 1994).

Selective non-catalytic reduction

While no SO2 is oxidised by the selective non-catalytic reduction SNCR system, SO3 concentrations in the

combustion gases are sometimes high enough (especially from higher sulphur coals) to be a concern when

occurring with potentially high ammonia slip rates. While these compounds can precipitate onto air

preheater basket surfaces and cause problems of fouling and plugging, this is beyond the remit of this study.

Sorbent injection

Furnace sorbent injection involves the direct injection of a dry sorbent into the gas stream of the boiler

furnace. The surface of these particles reacts with the SO2 in the flue-gas. Typical sorbents include:

pulverised limestone (CaCO3) and dolomite (CaCO3·MgCO3). In the furnace, the addition of heat results in

calcination of the sorbent to produce reactive CaO particles. Furnace sorbent injection provides the added

benefit of removing SO3, however its effects on the ratio of SO2 and SO3 could not be determined (European

Commission, 2013).



5. Summary and Recommendations

5.1 Summary

The review of the legislative text for the EU NECD and UNECE CLRTAP Gothenburg Protocol has identified

that differences occur in the way that emissions of sulphur are defined. In particular it is clear that for

CLRTAP a broader distinction is used which encompasses all forms of sulphur emitted to air, which is to be

expressed as SO2. However in terms of the related policy and international conventions, which includes the

major reference guides to aid inventory compilers, the main focus is SO2 only. This differing approach has

the potential to create a data gap and under-reporting for CLRTAP based on the definitions provided in the

Gothenburg Protocol.

Given these differences it has been important to understand the relationship between different forms of

sulphur and what proportion the non SO2 species make up in terms of total sulphur emissions. A review of

the major point sources categories for sulphur emissions (defined based on the nomenclature for reporting

(NFR) index system for sources) has highlighted that SO2 is the dominant form making up greater than 95%

of total sulphur emissions for the majority of cases. This means however that typically up to 5% of the

sulphur emission budget is contained within SO3 and non-oxide forms of sulphur which may or may not be

reported under CLRTAP and should not be included within NECD.

A further review of the abatement equipment in use, has shown that SCR has the potential to create SO3

from SO2 through oxidation in the emission gas stack and that FGD can case a shift in the ratios of SO2:SO3

depending on whether wet or dry limestone scrubbers are used. However these forms of abatement

equipment are also noted to remove such fractions from the waste gas as part of the abatement process.

This would suggest that the use of SCR and FGD types of emission abatement contribute to the SO3

emissions to air, but that overall the quantity is small, and that SO2 is still dominant at 95% or greater.

The review of non-oxide sulphur emissions has highlighted a range of species which can be emitted from

point sources, with much of the key reference data coming from Australian inventory compilation. Sources of

data for European inventory compilation was less prevalent. The combined emission of these non-oxide

sulphur species is likely small but may affect specific source sectors differently. It is estimated on the basis

of very limited data that reduced sulphur compounds account for up to 2-3% of total sulphur emissions from

most relevant industrial processes. For the paper and pulp industry, reduced sulphur compounds may

account for approximately 10% of total sulphur emissions, or more if gases containing these compounds are

not collected and abated.

Overall the contribution of industrial sources to total sulphur emissions is likely to be small, with natural

sources also a major consideration for emissions.

5.2 Recommendations

Based on the review completed, a mis-match has been identified between the definitions in use for CLRTAP

and the NECD. Furthermore much of the related policy at EU and UN level relates to SO2 rather than the

definition set out in article 1 of the Gothenburg Protocol (all forms of sulphur reported as SO2) as the

recognised pollutant for emission estimation and hence for compliance checking with reduction targets and

limit values. However the amended Gothenburg Protocol from 2012 (not yet adopted) does aim to amend

this issue with Article 3.11 that requires parties to provide an inventory and projections of SO2 and emission

ceilings which are defined for SO2. Where SO2 dominates the combustion emissions with 95% or greater of

the total sulphur emissions, the likely ‘gap’ is small.

However there is a need for greater clarity and transparency in emission inventory reporting to aid

comparability within the CLRTAP inventories, but also in comparison to other reporting requirements.

Therefore on that basis three possible options would be open to review:

Option 1: Amendment of the Gothenburg Protocol Article 1 to amend the definition of ‘sulphur’ to

bring in it alignment with the NECD and related legislation. This option would remove any ambiguity



in the definitions and resolve potential compatibility issues assuming that the majority of inventories

will be based on SO2. However this option would also exclude SO3 and non-oxide forms of sulphur

which do contribute to the overall atmospheric emissions budget and sulphur deposition. It should

be noted that the Gothenburg Protocol as amended still refers to "sulphur" with regard to the

indicative reduction commitments for the USA (footnote to annex II, table 2), whereas the revised

(amended) annex II refers to SO2 only.

Option 2: Amendment of the National Emission Ceilings Directive to amend the definition of ‘sulphur’

to bring it into alignment with the Gothenburg Protocol. This option would remove any ambiguity in

the definitions and resolve potential compatibility issues assuming that a number of inventories will

be based on all forms of sulphur expressed as SO2. While this option would close a data gap and

ensure continuity between the Protocol and Directive, it may have consequences for emissions

targets for some EU Member States. Where emission ceilings have been agreed, revision of the

definitions and need for additional work to revise inventories to include missing non-sulphur dioxide

proportions may mean that some Member States are no longer able to meet the previously agreed

targets..

Option 3: Develop the guidance provided by TFEIP and EMEP to Inventory compilers to remove

ambiguity. This option can work one of two ways, either there is an agreement that "sulphur"

principally means SO2, and therefore inventories should be based on SO2 to ensure comparability

between each other and NECD. The second method would be to enforce the article 1 definition and

make clear within the guidebook where emission factors are SO2 only and where emission factors

are for sulphur emissions expressed as SO2. This could mean the need for additional reference to

reflect SO2 and total sulphur within the guidance. This option would ensure continuity for reporting

under CLRTAP and help define the difference between CLRTAP and NECD estimates. However it

may also represent the need for revisions of both existing inventories and the guidelines for reporting

and the EMEP/EEA guidebook itself.

Option 4: Accept the amendments as they are.

Agree to interpret the 2012 amendment of the Gothenburg Protocol as only referring to obligations

for total sulphur for the 2020 reduction commitments and align EU legislation thereto. This would

require agreeing an interpretation of the CLRTAP modifications, also with other non-EU parties of

those alterations.

Option 5: Recognise that differences exist within the interpretation of how ‘sulphur’ is defined for

estimation and reporting under different international policy instruments; but take no further action on

the basis that the impact on overall reported emissions is likely to be small for most countries and

sectors.



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Appendix A Further information on EU reporting requirements for sulphur

Section 2 of this report provides a review of the major reporting requirements for sulphur under the NECD

and Gothenburg Protocol, as well as a range related policy instruments, covered by the European Union and

wider international community. This is intended to provide the ‘current’ picture for international reporting

requirements. However both the NECD and Gothenburg Protocol have been subject to evolution since their

respective creations. This Appendix provides a brief overview of the details for key developments in sulphur

reporting.

The information below has been provided by the European Commission as a brief documented history of

changes to reporting and reporting guidance, which include:

Convention on Long Range Transboundary Air Pollution 1979:

• Art8a. “Data on emissions at periods of times to be agreed upon, of agreed air pollutants, starting with

sulphur dioxide,...”

First sulphur protocol 1985:

• Art4. “Each party shall provide annually to the Executive Body its levels of national annual sulphur

emissions...” [no definition of sulphur provided]

Second sulphur protocol 1994:

• “Sulphur emissions means all emissions of sulphur compounds expressed as kilotonnes of sulphur

dioxide...”

Gothenburg protocol 1999:

• Art 1.10: "Sulphur" means all sulphur compounds, expressed as sulphur dioxide (SO2);

• Annex II Table 1 Emission ceilings [2010] for sulphur (thousands of tonnes of SO2 per year)

• Annex III Table 1. Limit values for SOX emissions released from boilers. [But USA and Canada SO2 is

referred to]

Gothenburg protocol amended 2012:

• Art 1.10: "Sulphur" means all sulphur compounds, expressed as sulphur dioxide (SO2) [text stayed

untouched from the original 1999 protocol];

• Art 2.1 The objective of the present Protocol is to control and reduce emissions of sulphur...

• “Emissions of sulphur,” is used in the document a number of times e.g. Art 3 Paragraph 10 shall apply

to any Party: ... (b) Whose annual emissions of sulphur,...

• Art 3.11 ter. Each Party shall develop and maintain inventories and projections for the emissions of

sulphur dioxide...[altered from the original protocol where it refers to sulphur]

• Annex II Table 1 includes the [2010] emission ceilings for sulphur dioxide (SO2),...

• Annex II Table 2. Emission reduction commitments for sulphur dioxide for 2020 and beyond

Convention decisions

• Decision 2013/4 ‘Reporting of emissions and projections data under the Convention and its protocols

in force’ expressly clarified certain reporting requirements for the Convention and its protocols, including for

the Convention, that “The air pollutants, referred to in article 8, paragraph (a), of the Convention shall be

emissions of: sulphur (SOX)...”. [The decision hence does not refer to the GP as amended and once the

amendment enter in force the decision may have to be revised]



Convention reporting guidelines

Under the Convention on Long Range Transboundary Air Pollution there are also a set of official ‘Reporting

Guidelines of the Convention’, which specify more practically which pollutants should be reported. These

documents (rather than the protocols) are used by the emissions reporting community. Ideally these

documents should be consistent with the protocol texts, but over the course of the Convention and Protocol’s

evolution this hasn’t always been the case. However, in practical terms, the reporting guidelines are key

implementing documents. The evolution of these documents shows:

The 1997 first version of the Guidelines (EB, AIR/GE.1/1997/5):

• required reporting of annual national emissions of sulphur dioxide SO2.

The 2002 Reporting Guidelines (EB.AIR/GE.1/2002/7) were subsequently aligned with the 1999

Gothenburg reporting requirements, but with further information namely:

• 8. The air pollutants covered by the present guidelines are: sulphur,...

• Annex I. "Sulphur" means all sulphur compounds, expressed as sulphur dioxide (SO2). Note: The

major part of anthropogenic emissions of sulphur oxides to the atmosphere is in the form of SO2 and,

therefore, emissions of SO2 and SO3 should be reported as SO2 in mass units. Emissions of other S

compounds such as sulphate, H2SO4 and non-oxygenated compounds of sulphur, e.g. H2S, are less

important than the emissions of sulphur oxides on a regional scale. However, they are significant for some

countries. Therefore, Parties are also recommended to report emissions of H2SO4, sulphates, and total

reduced sulphur (TRS) as SO2 in mass units. All anthropogenic sources of sulphur oxides should be

considered

The 2009 Reporting Guidelines (ECE/EB.AIR/97)

• Total national emissions by NFR source category SOX

The 2014 Reporting Guidelines (ECE/EB.AIR/97)

• Art 7a The substances for which there are existing reporting obligations in the Convention and the

protocols as further specified by Executive Body decision 2013/4, include:

• (a) “Sulphur” (SOX), which means all sulphur compounds expressed as sulphur dioxide (SO2)

(including sulphur trioxide (SO3), sulphuric acid (H2SO4), and reduced sulphur compounds, such as hydrogen

sulphide (H2S), mercaptans and dimethyl sulphides, etc.)

• The Guidelines raise the possibility that Parties may diverge from the pollutant definitions - footnote 4:

“Any departure from the definitions provided in this paragraph should be clarified in the IIR”.

EMEP/EEA Guidebook

Over time the information in the Guidebook has changed – the first version and until 2007 included

emission factors for sulphur dioxide SO2. The original CORINAIR inventory was for sulphur dioxide SO2.

With the major update of the Guidebook in 2009, a change was made to express emissions factors as SOX,

to bring the Guidebook into line with the 1999 Gothenburg protocol reporting requirements and the then

in-force 2009 Reporting Guidelines. It is unclear whether this update and realign addressed changes to the

emission factors in use, or whether the data for SO2 factors were relabelled to become SOX, which might

represent an under reporting issue.

Continued improvements of inventory quality of …ec.europa.eu/environment/air/pdf/sulphur...

Documents

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