AIR POLLUTANTS. SOURCES AND MEASUREMENT...

1

CM4112

AIR POLLUTANTS. AIR POLLUTANTS.

SOURCES AND MEASUREMENT METHODSSOURCES AND MEASUREMENT METHODSDr. Amalia Muñoz

Fundación CEAM. Euphore Laboratories

[email protected]

The composition and chemistry of the atmosphere is of importance because of the interactions between the atmosphere and living organisms.

The composition of the Earth's atmosphere has been changed by human activity and some of these changes are harmful to human health, crops and ecosystems.

Examples of problems:

ACID RAINS (ACID PRECIPITATION): Deposition of acidic components in rain, snow, fog, dew, or dry particles. Occurs when SO2 and NOx are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds. The droplets then fall to earth as rain, sn, snow or sleet.

PHOTOCHEMICAL SMOG: mixture of air pollutants, usually highly reactive and oxidizing including: NOx, tropospheric ozone, VOCs, PAN, Aldehydes, etc.

GLOBAL WARMING: Observed increase in the average temperature of the Earth’s Atmosphere and ocenas in recent decades.

AIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSAIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSIntroduction

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AIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSAIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSIntroduction

trace to 0.00080O3Ozone0.00001XeXenon0.00003N2ONitrous Oxide0.00005H2Hydrogen0.00011KrKrypton0.00017CH4Methane0.00052HeHelium0.00182NeNeon0.035CO2Carbon Dioxide0.934ArArgon20.947O2Oxygen78.084N2Nitrogen

Mole PercentSymbolConstituent

And NO2, NH3, SO2, VOCs, etc

AIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSAIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSNITROGEN COMPOUNDS

Organic N (R-NH2)

Nitrates (NO3-) Ammonium (NH4

+)

Nitrites (NO2-)

Denitrification

Nitrification Nitrification

Natural Fixation

Leaching Leaching

MineralizationPlant Uptake

Gaseous Loss to Atmosphere(N2, N2O, NO)

Precipitation

Organic Residues Livestock &

Sewage Waste

Fossil Fuel Combustion

Fertilizer

3

AIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSAIR POLLUTANTS. SOURCES AND MEASUREMENT METHODS

Nitrogen dioxide: NO2Nitric oxide: NONOx: NO + NO2

Nitric acid: HNO3Nitrous acid: HONO

Nitrate radical: NO3Dinitrogen pentoxide: N2O5

Organic nitrates RONO2Peroxy acetyl nitrate (PAN) CH3C(O)OONO2

NOy: NOx + HONO + HNO3 + NO3 +N2O5 + PAN + alkylnitrates(The nitrogen is in an oxidation state of 2 or greater)

NITROGEN COMPOUNDS

Important for assessment of air quality. NOx chemistry

Nitrogen compounds are present in the atmosphere in both oxidised and reduced forms. The reduced compounds include ammonia (NH3) and ammonium (NH4).

Nitrogen oxide: N2OOxidised compounds emitted to the atmosphere due to bacterial activity in the soil. It

is emitted also from anthropogenic sources (e. g. catalytic reduction processes) and acts as a greenhouse gas.

AIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSAIR POLLUTANTS. SOURCES AND MEASUREMENT METHODSINORGANIC NITROGEN COMPOUNDS

NOxNOx. Sources. Sources

Biogenic emissions: Denitrification and losses to the atmosphere

Direct Antropogenic emissions: Mainly combustion sources, where NO is formed by reaction between the nitrogen and the oxygen in the combustion air and to some extent by oxidation of nitrogen in the fuel.

30 to 50 million tons per year from human activities, 10 to 20 million tons per year from natural sources

Photochemical Reactions

Nitrogen oxides are emitted mainly (in most cases >90%) as NO. NO2 is formed relatively rapidly from NO by reaction with ozone or radicals, such as HO2 or RO2.

Via a number of different atmospheric reactions some nitrogen oxides will finally become HNO3/NO3-, which, with NO2 are removed from the atmosphere via wet and dry deposition processes.

Although it is not the major nitrogen oxide species in all areas, NO2 is one of the most important air pollutants in urban areas, as it is the most significant nitrogen oxide species from a human health point of view.

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EU15: 9372 GgEU27: 11603 Gg

Source: CORe Inventory AIR project (CORINAIR). European Monitoring and Evaluation Programme (EMEP)

Belgium

Cyprus

DenmarkFinland

France

Germany

Hungary

Italy

Lithuania

Netherlands

Poland

Romania

Slovakia

Spain

Switzerland

0200400600800

10001200140016001800

NO

x, G

g (1

000

tonn

es)

Aus

tria

Cyp

rus

Est

onia

Ger

man

y

Irela

nd

Lith

uani

a

Mal

ta

Pol

and

Ser

bia

and

Mon

tene

gro

Spa

in

Uni

ted

Kin

gdom

Countries

NOx Emissions in Europe, 2004



Belgium

Cyprus

DenmarkFinland

France

Germany

Hungary

Italy

Lithuania

NetherlandsPoland

Romania

Slovakia

Spain

Switzerland

-60.00%

-50.00%

-40.00%

-30.00%

-20.00%

-10.00%

0.00%

10.00%

20.00%

30.00%

NO

x, %

cha

nge

com

pare

d to

19

90

Aust

ria

Bulg

aria

Cze

ch R

epub

lic

Esto

nia

Fran

ce

Gre

ece

Irela

nd

Latv

ia

Luxe

mbo

urg

Mal

ta

Nor

way

Portu

gal

Serb

ia a

nd M

onte

negr

o

Slov

enia

Swed

en

Uni

ted

King

dom

Countries

NOx Emissions in Europe, 2004

5


NOx emissions. EU15. Sources

Agriculture179.975

1.6%Waste30.3920.3%

Other (Energy)609.451

5.5%

Other (non-energy)0.0690.0%

Memo items (not included in National

Total)1711.625

15.4%

Industry (Processes)

180.631.6%

Other transport (non-road mobile

machinery)1344.281

12.1%

Road transport3877.235.0%

Fugitive emissions26.9520.2%

Industry (Energy)1335.048

12.0%

Energy industries1785.282

16.1%


NOx emissions. Ireland. Sources

Agriculture

0.0%Waste

0.0%

Other (Energy)7.4685.8%

Other (non-energy)

0.0%Memo items (not

included in National Total)13.49510.4%


0.0% Other transport (non-road mobile

machinery)14.7

11.4%


Fugitive emissions

0.0%

Industry (Energy)16.68812.9%

Energy industries33.29225.8%

NOx emissions. Spain. Sources






machinery)231.79410.9%


10.2910.5%


Total)573.7527.1%

Other (non-energy)

0.0%


Waste3.560.2%

Agriculture16.2910.8%

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From Chemical Reactions in Air

NO2 + hυ → NO + OO + O2 → O3

M

HONO + hυ → NO + OH

HNO3 + hυ → NO2 + OH

NO3 + hυ → NO2 + O(3P)

NO3 + hυ → NO + O2

N2O5 + hυ → NO2* + NO3

N2O5 + hυ → NO + NO3 + O



RONO2 + hυ → NO2 + RO

CH3C(O)OONO2 + hυ → NO2 + CH3C(O)OO

CH3C(O)OONO2 + hυ → NO2 + CH3C(O) + O2

HO2 + NO → NO2 + OHRO2 + NO → NO2 + RO

HO2 + NO3 → NO2 + OH + O2

From Chemical Reactions in Air

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Cycle of inorganic nitrogen compounds in an urban environment Cycle of inorganic nitrogen compounds in an urban environment


1. Chemiluminiscence with O3

Analysis of NO

The NO molecules react with ozone to form the activated species NO2* according to the next mechanism:

NO + O3 → NO2* + O2NO2* → NO2 + hυ

As the activated species, NO2*, reverts to a lower energy state, it emits broad-band radiation from 500 to 3000 nm, with a maximum intensity at approximately 1100 nm.

The intensity of the chemiluminescent reaction is directly proportional to the NO concentration in the sample. The photomultiplier current is then proportional to the chemiluminescent intensity.

NOxNOx. Measurement methods. Measurement methods

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Analysis of NO2 and NOx

by chemically reducing NO2 to NO,

This conversion is accomplished with a converter that pneumatically switches in and out of the sample stream in cycles.

This switching creates a time-phased sample stream composed of NO and NOx samples. The NOx cycle measures both, the NO and NO2 in the sample, while the NO cycle measures only the NO.

The NO2 concentration is derived by subtracting the NO signal from the NOx signal.






Converters:Thermal converter

Catalytic converter heated molybdenum to reduce any NOx present to NO by the following reaction at 315 ºC:

3NOx + Mo → 3NO + MoO3

Photolytic converter performs a selective conversion of NO2 to NO through photodissociation with a xenon lamp.This method permits a selective conversion higher than any thermal or catalytic converter, in which many components other than NO2 (HNO3, NH3, PAN, etc) can also be converted to NO


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Converters:Thermal converter

Catalytic converter heated molybdenum to reduce any NOx present to NO by the following reaction at 315 ºC:

3NOx + Mo → 3NO + MoO3

Photolytic converter performs a selective conversion of NO2 to NO through photodissociation with a xenon lamp.This method permits a selective conversion higher than any thermal or catalytic converter, in which many components other than NO2 (HNO3, NH3, PAN, etc) can also be converted to NO




real-time operationweightportability

Resolution time: around 1 minute. Integrated around 5 minutes or 1 hour.

Range: from few pptv to several ppmv

Interferences : Nitrogen containing compounds

Thermal converter > catalytic converter > photolytic converter

The most common and used method


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2. Remote sensing, DOAS (Differential Optical Absorption Spectroscopy)


Open path optical measuring technique applicable for a number of gases, including NO2specifically, absorbing light in the UV and visible spectral regions.

The technique is based on differential absorption, i.e. the difference between local maximums and minima in the absorption spectrum of the probed gas. The DOAS technique may also be used for NO, but a shorter path is required than for NO2.

Light from a broad-band xenon high-pressure lamp is transmitted up to severalkilometres through the atmosphere. The light is received and analysed by the use of a fast scanning dispersive spectrometer to eliminate the influence of air turbulence.

The DOAS technique is used today in a large number of applications.

The major advantage of DOAS is that several compounds can be measured at the same time, i.e. HONO, NO3 radicals, benzene, toluene etc.

To be explained in more detail in following lectures


3. Discontinuous methods


The manual discontinuous methods are relatively cheap and simple, but have several disadvantages including the need for manpower for sampling and analysis, the limited time resolution and the time delay until results are available.

Active methods: the potassium iodide and the Saltzmann methods

The potassium iodide method is based on the absorption of NO2 on a potassium iodide impregnated sintered glass filters. NO2 is absorbed and reduced to nitrite by the iodide on the filter. The nitrite formed is extracted with deionised water and determined spectro-photometrically.

The Saltzmann/modified Saltzmann method is based on the direct Griess reaction during sampling. A pink colour is produced during sampling. The intensity is measured spectro-photometrically. Diffusion denuders combined with an analysis by ion chromatography may also be used for the determination of NO2.

Carbon coated denuders allow for the simultaneous determination of NO2 and PAN at concentration levels which approach 50 ppt (on a 24 hour basis which makes the technique very suitable for the measurement of NO2 in rural areas.

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3. Discontinuous methods


Passive methods:Used for longer sampling periods, on weekly (usually in more polluted areas) or monthly (usually in less polluted areas) basis.

The sampling technique is based on molecular diffusion of the gas molecules into the sampler, where they are quantitatively collected on an impregnated filter. No electricity, pump or other equipment (except for a rain shelter) is needed.

Diffusive samplers are simple and cheap and the procedure can produce a large amount of long term air quality data to a fairly low cost. In combination with other measurements with higher temporal resolution, the passive sampling is valuable for the total air qualityassessment. However the diffusive samplers need validation.

The NO2 collected on the impregnated filter is extracted from the filter with water anddetermined by chemical analysis. When calculating the concentration, the ambient airtemperature must be taken into consideration, since the diffusion velocity is temperature dependent.


Analysis of HNO3 at the low levels typically found in the atmosphere is difficult, in large partdue to its tendency to adsorb very readily to surfaces.

As a result, sampling HNO3 in an artifact-free manner is often the limiting aspect in making accurate measurements.

Several different methods exist for measuring HNO3, most commonly FTIR and TDLS,. Other techniques commonly used include filters, denuders, transition flow reactors, and scrubbers, followed by analysis of the collected material for nitrate, e.g., by ion chromatography.

INORGANIC NITROGEN COMPOUNDS

HNOHNO33. Sources and measurement methods. Sources and measurement methods

NO2 + OH → HNO3 (gas phase)

2NO2 + H2O → HNO3 + HONO (heterogeneous process)

NO2 + O3(or H2O2) → NO3 + O2 (night chemistry)NO3 + NO2 → N2O5N2O5 + H2O → HNO3

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NO3 can be measured using visible spectroscopy and its absorption bands, particularly the one at 662 nm.

NONO3 3 radical. Sources and measurement methodsradical. Sources and measurement methods

NO2 + O3 → NO3 + O2

NO3 + hυ → NO2 + O(3P)

NO3 + hυ → NO + O2

Only exist in sufficient concentrations to play a role in nighttime chemistry, due to its strong absorption of light in the visible and subsequent photodisociation



Important as an OH source by photolysis at day, particularly in polluted Areas.


HONO. Sources and measurement methodsHONO. Sources and measurement methods

HONO enhances photo-oxidation processes early in the morning due to the production of OH radicals at a time of the day when other OH sources are still small

HONO + hυ (300<λ<405nm) → NO + OH

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HONO is also a major source of OH radicals during the day.

The formation mechanism in the atmosphere are not well understood yet

It is commonly accepted that HONO is formed by heterogeneous processes, i.e. conversion processes of NO2 on humid surfaces.



Measurement methodsMeasurement methods

1. DOAS.

It is very selective, and free of sampling artifacts and chemical interferences.

Detection limits, in the order of 100 ppt

Daytime concentrations are only detected in highly polluted environments or at low solar irradiation levels

Expensive system components



2. FTIR and cavity ring down spectroscopy


Detection limits, in the order some ppb. Not sufficiently sensitive to detectHONO during the day.

2. Chemical in situ techniques

Instruments cheaper, easier to use and more sensitive.

Detection limits: 1ppt

Suffer from chemical interferences in the sampler and sampling artifacts in the sampling lines (HONO can be formed heterogenously in these surfaces)

Wet Effluent denuders (WEDD): Interferences of chemical reactions of NO2 with hydrocarbons

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A new sensitive monitor has been recently developed:

LOPAP LOPAP (Long path absorption photometer)

Other instruments: HONO + H2O NO2

- + H3O+

NO2 + SO2 NO2- + HSO3

-

IV IV III VI

NO2 +

O-

NO2- + products

Interferences






HONO + H+ NO+ + H2O

+NH2NH2-SO2 NO+ N2+NH2-SO2 H2O+

N2+

SO2-NH2

NH2+Cl-

NH3+Cl-

+ NH2+Cl-

NH3+Cl-

NNNH2-SO2

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130-50Chemical detector, Effluent: 1 N HCl/Sulfanilamid (pH = 0)

LOPAP

4200Chemical detector, Effluent: Na2HPO4Buffer (pH = 7)

HPLC

8300Chemical detector, Effluent: H2OWEDD

1-4200-1500UV-AbsorptionDOAS

Time Resolution [min]

Detection limit [pptV]

Measurement principleMeasuring instrument

Comparison of the system parameters of the different HONO measuring instruments, which were used for the exhaust measurements in the EUPHORE Smog chamber


Organic compounds play a key role in the formation of ozone,particles, and other species of interest.

Some of the individual species are of concern from the point ofview of health effects e.g., the carcinogens benzene and 1,3-butadiene.,

For most VOC it is because of their central role in the formation of ozone and associated pollutants

NON-METHANE HYDROCARBONS AND VOLATILE ORGANIC COMPOUNDS

SourcesSources

NO2 + hυ → NO + OO + O2 → O3

M

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SourcesSources

Biogenic sources:

Vegetation: isoprene, monoterpenes (C10H16), sesquiterpentes (C15H24), and oxygenated NMOCS (including methanol, 2-methyl-3-butenol, 6-methyl-5-hepten-2-one, cis-3-hexenol, cis-3-hexenylacetate, linalool, etc.)

Anthropogenic sources:

Including combustion sources (vehicle and fossil-fueled power plant emissions), fuel storage and transport, solvent usage, emissions from industrial operations, landfills, and hazardous waste facilities

World-wide emissions: 60-140 millions tons per year

World-wide emissions: 1150 millions tons per year



Anthropogenic Sources Anthropogenic Sources VOCS Emissions in Europe 2004

0

200

400

600

800

1000

1200

1400

1600

Austria

Belgium

Bulgari

a

Cyprus

Czech

Rep

ublic

Denmark

Estonia

Finlan

d

France

German

y

Greece

Hunga

ry

Irelan

dIta

lyLa

tvia

Lithu

ania

Luxe

mbourg

Maced

onia-

the F

ormer

Yugos

lav R

epub

lic of

Malta

Netherl

ands

Norway

Poland

Portug

al

Roman

ia

Serbia

and M

onten

egro

Slovak

ia

Sloven

iaSpa

in

Sweden

Switzerl

and

United

King

dom

EU countries

VOC

s em

issi

ons

Gg

(100

0 to

nnes

)


17



Direct sources of VOCS emission in EU. 2004


848.7317%

Agriculture412.241

3%

Waste104.811

1%

Other (Energy)1050.299

8%


machinery)471.03

4%

Road transport2182.018

17%

Fugitive emissions734.295

6%

Energy industries94.084

1%

Industry (Energy)162.799

1%

Other (non-energy)3900.769

29%


Total)2962.659

23%

Source: COReInventory AIR project (CORINAIR). European Monitoring and Evaluation Programme (EMEP)

Anthropogenic Sources Anthropogenic Sources



Direct sources of VOCS emission in Ireland. 2004


0%Agriculture

3.3045%

Waste

0%

Other (Energy)4.8057% Other transport (non-

road mobile machinery)

2.0383%

Road transport21.52933%

Fugitive emissions6.86511%

Energy industries0.3431%

Industry (Energy)0.5561%

Other (non-energy)24.28838%


Total)0.641%

Direct sources of VOCS emission in Spain. 2004

Industry (Processes)207.0610.18%

Agriculture1.5190.07%

Waste28.4161.40%


Other transport (non-road mobile machinery)

24.0791.18%





Other (non-energy)503.08724.73%


Total)910.90244.79%



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EU27EU15Austria

Belgium

Bulgaria

Cyprus

Czech RepublicDenmark

EstoniaFinland

France

Germany

Greece

Hungary

Ireland

Italy Latvia

LithuaniaLuxembourg

Malta

Netherlands

Norway

Poland

Portugal

Romania

Slovakia

Slovenia

Spain

Sweden

Switzerland

United Kingdom

-70%

-60%

-50%

-40%

-30%

-20%

-10%

0%

10%

20%

VOCs Emission in Europe. 2004. % changed compared to 1990





Total nonTotal non--methane organics NMOCmethane organics NMOC as a group i.e., non-speciated, are commonly measured by cryotrapping the air sample, e.g., in liquid argon, which does not trap CH4. The contents of the trap can then be thermally desorbed directly into a flame ionization detector FID

SpeciatedSpeciated measurements of individual organicsmeasurements of individual organics: The almost universal approach to the identification and measurement of individual VOC is GC with either FID or mass spectrometry

sample preconcentration is required.

This is typically accomplished by direct cryotrapping of air, trapping on a solid sorbent, or sampling into an evacuated canister followed by cryotrapping the canister contents prior to injection onto the GC column.Removal of ozone prior to trapping the organics is highly desirable

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Gas Chromatography (GC)

Basic components

Acquisition and processing system

Carrier gas

Pressure Regulator and Flow controller

Oven

Column

Injector Detector




1• Solid phase microextraction (SPME) is suitable for

sampling environmental contaminants with a wide range of physical properties in air, water and soil.

• A fused silica fibre with a polymer coating is exposed to the sample or the headspace above the sample.

• Organic analytes adsorb to the coating on the fibre. After adsorption equilibrium is attained, usually in 2 to 30 minutes, the fibre is withdrawn.

• The fibre is introduced into a GC injector, where the adsorbed analytes are thermally desorbed and delivered to the GC column.

• The amount of analyte adsorbed by the fibre depends on the thickness of the polymer coating and on the distribution constant for the analyte.

• Fibres with a range of different polarities are now commercially available.

Solid Phase Microextraction (SPME)





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1Direct Thermal Extraction

• Permits the direct thermal extraction of volatile and semi-volatile organics directly from small sample sizes (mg) without the need for solvent extraction or other sample preparation requirements.

• The sample is maybe trapped on sorbent resins or placed inside a preconditioned glass-lined stainless steel desorption tube.

• The desorption tube containing the sample is then connected to a short path thermal desorptionsystem.

• The desorption tube is ballistically heated and carrier gas carries the analytes through the injection port and onto the GC column for analysis.





1Use of cartridges or filters

• Need for solvent extraction

• The sample is trapped on sorbent resins





PUFCoconut charcoalXAD-2 PTFE filterGlass fiber filterSilica gelTenaxetc

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Quantitative Analysis

Chromatogram

The response must be linearConcentrationMass

The response factor of each compound is different for each compound

Parameters that can be used:

Peak HeightPeak Area





HYPHENATED TECHNIQUES in ChromatographyHYPHENATED TECHNIQUES in Chromatography

Chromatographic Techniques

Spectroscopic Techniques

Separation of analytes

Necessity of pure

analytesLow security

in identification

High identification

level

+ - + -

Hyphenated techniques provide the analyst with structural information on the components present in complex mixtures.This information may be sufficient to identify components

On-line combination of a chromatographic separation technique with a sensitive and Element-specific detector





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Gas Chromatography

Mass Spectrometry

Infrared Spectroscopy

Emission and Absorption

Atomic SpectroscopyNuclear Resonance

Spectrometry

Liquid Chromatography

GC-MSG

C-FT

IR-M

S

GC-FTIR

GC-AAS

LC-MS

LC-FTIR

LC-ICP

LC-NMR

Common hyphenated techniques





GC-MS




23


Carbonyl compounds.Carbonyl compounds.

SourcesSources


Products

Carbonyl + alcohol

NMOC ·R

O2

RO2· ROONO2ROOH

RO·

HO2·

NORONO22

RO2·

NO2

Alkene + O3 Carbonyl + biradical(two sets)


Carbonyl compounds. Measurement methodsCarbonyl compounds. Measurement methods


•2,4-Dinitrophenyl hydrazine derivates are one of the most frequent used techniques to determine atmospheric concentrations of carbonyl compounds. This technique is based on the acid catalysed derivatization of aldehydes and ketones to form intense coloured hydrazones. Those hydrazones can be separated using standard HPLC-UV techniques and quantified by its response at a specific wavelength. The UV detector for quantification is set for simple n-chain derivatives to 360 nm and for di-carbonyls to 400 nm. To collect the aldehydes/ketones commercially available silica gel cartridges are used. The air flow is controlled by a thermal mass-flow device and the cartridges are eluted after collection with acetonitrile in a volumetric flask.

•The other available technique is a DOAS (Differential Optical Absorption Spectrometer) system with in-situ optical absorption cell inside the simulation chamber. The instrument records the spectra of formaldehyde caused by its UV absorption and calculates the concentration using a mathematical treatment to minimize the residual obtained by subtracting a known reference spectrum.

Low detection limits in the range of a few ppb are achieved.

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HCHO. Hantzsh reaction

• The detection of formaldehyde is based on the liquid phase reaction of formaldehyde with acetylacetone (2,4-pentadione) and an amine (“Hantzsh”-reaction). This reaction produces α-α’-dimethyl-β-β’-diacetylpyridine, that is excited at 400 nm (Hg-lamp) and the fluorescence is detected at 510 nm. The technique is sensitive to formaldehyde in aqueous solution.

• The reactions are carried out in aqueous solution. For the measurement of gaseous formaldehyde, this first has to be transferred into aqueous solution. This is achieved in a stripping coil where air and stripping solution is brought into contact at defined flow rates and contact surfaces. The air and liquid streams are afterwards separated and the solution is then analyzed for formaldehyde.

• The HCHO mixing ratio in air is then calculated from the concentration in solution and the ratio of air and stripping flow rates.

HH

O+ + 2NH3

O O

NH

OO


Carbonyl compounds. Measurement methodsCarbonyl compounds. Measurement methods



They are formed in the VOCNOx photochemical cycles,

The highest levels of PAN are often seen downwind of urban areas rather than in the center. Peak concentrations of PAN in or downwind of major urban areas during periods of high photochemical activity can reach levels as high as 35 ppb

PAN, OTHER PEROXYNITRATES, AND ALKYL NITRATES

SourcesSources

Products

Carbonyl + alcohol

NMOC ·R

O2

RO2· ROONO2ROOH

RO·

HO2·

NO RONO22RO2·

NO2 CH3CHO + OH → CH3CO + H2O

CH3CO +O2 +M → CH3C(O)OO+ M

CH3C(O)OO +NO2 +M → PAN + M

25



SourcesSources

PAN → CH3C(O)OO +NO2Heat

Reservoir for a long-range transport of NOx in the troposphere

VOCs NOx

PAN

PAN

NOx

NOx Source Region Remote atmosphere

Long-range transport at low temperatures

HNO3

HNO3


Air samples are collected automatically in a sampling loop and then injected into the chromatograph.

For calibration of PAN, a dynamic generation of defined gas phase PAN-concentrations at ambient temperatures is used by means of compounds easily regulated and controlled.

NO is used as the concentration determining compound. This allows PAN-measurements to be linked directly to NOx standards in the gas phase.

•These compounds are almost universally measured using gas chromatography with electron capture detection ECD.,

•A luminol chemiluminescence detector has also been used in which PAN is thermally decomposed to NO2 at the end of the column and the NO2 measured

•In polluted atmospheres where the concentrations are higher, FTIR has also been used.

GCGC--ECDECD. InIn--situ PAN generationsitu PAN generation.



26


Tropospheric ozone is the precursor of OH and plays therefore a key role in maintaining the oxidizing power of the troposphere.

It is also of environmental importance as a greenhouse gas and as a toxic pollutant in surface air. In densely populated regions with high emissions of NOx and hydrocarbons, rapid O3production can take place and result in a surface air pollution problem.

Ozone is not emitted directly but is a photochemical pollutant formed when volatile organic compounds (VOCs) interact with nitrogen oxides under the influence of sunlight. The control of ground-level ozone concentrations is thus achieved by the control of emissions of VOC and NOx

OZONE

NO2 + hυ → NO + OO + O2 → O3

M

O3 can be also supplied to the troposphere by transport from the stratosphere,

NO + O3 → NO2 + O2

SourcesSources


OZONE

The photochemistry of ozone formation in simplified form

VOC + OH + O2 → RO2 + H2O

RO2 + NO + O2 → NO2 + HO2 + CARB

HO2 + NO → NO2 + OH

2(NO2 + hv +O2 → NO + O3)

Net: (NOx + OH +) VOC + 4O2 → 2O3 + CARB + H2O (+ NOx + OH)

NO2 + hυ → NO + OO + O2 → O3

M

SourcesSources

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OZONESourcesSources

SOURCES: 3400-5700 Tg/years

Chemical production: (NO2 + hv +O2 → NO + O3 ) 3000-4600

HO2 + NO → OH + NO2 (70%)CH3O2 + NO → CH3O + NO2 (20%)RO2 + NO → RO + NO2 (10%)

Transport from stratosphere 400-1100

SINKSChemical loss: 3000-4200

O(1D) + H2O → 2 OH (40%)HO2 + O3 → OH + 2O2 (40%)OH + O3 → HO2 + O2 (10%)others (10%)

Dry deposition 500-1500


OZONEMeasurement MethodsMeasurement Methods

• Chemiluminescence on reaction with NO or ethene: (The same principle used in the analysis of NO)

•DOAS

•TDLS

•Wet chemical methods, mainly those involving the oxidation of I to I2 and measurement of the I2 colorimetrically.

•Passive samplers: Primarily for use in epidemiological studies.

air containing ozone diffuses through a Teflon membrane and reacts with nitrite.

The sampler is then extracted and the nitrate product measured using ion chromatography.

•UV absorption at 254 nm

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OZONEMeasurement MethodsMeasurement Methods

UV absorption at 254 nm

Commercial instruments based on this absorption are in widespread use.

Typically, air is drawn into a cell and the absorption of the 254-nm line from a Hg lamp is measured.

The air stream is then switched to pass through a catalyst that destroys O3 and the absorption is again measured to provide 0.

Alternatively, two parallel cells are used, one of which has air from which O3 has been scrubbed and the other the air containing ozone.

Interferences: Compounds that absorb at 254 nm, the predominant wavelength emitted by the UV lamp, Including aromatics and SO2,

AIR POLLUTANTS. SOURCES AND MEASUREMENT...

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