BIOGENIC AEROSOL:SECONDARY ORGANIC AEROSOL (SOA)

PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

THE IMPORTANCE OF ORGANIC AEROSOL

[Zhang et al., 2007]Sulfate Organics

• Organic material contributes 20-50% of the total fine aerosol mass at continental mid-latitudes [Saxena and Hildemann, 1996; Putaud et al., 2004] and as much as 90% in the tropical forested areas [Andreae and Crutzen, 1997; Talbot et al., 1988; 1990; Artaxo et al., 1988; 1990; Roberts et al., 2001]

CloudProcessing

ORGANIC CARBON AEROSOL

Semi-Volatiles

Oxidation by OH, O3, NO3

Direct Emission

Fossil Fuel Biomass Burning

MonoterpenesSesquiterpenes

Nucleation or ReversibleCondensation

Aromatics Isoprene

Secondary

Organic

Aerosol

Primary

Organic

Aerosol

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated global

budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

SECONDARY ORGANIC AEROSOL PRODUCTION

VOC Emissions Oxidation

Reactions(OH, O3,NO3)

Nucleation (oxidation products) Growth

Condensation on pre-existing aerosol

Over 500 reactions to describe the formation of SOA precursors, ozone, and other photochemical pollutants [Griffin et al., 2002; Griffin et al., 2005; Chen and Griffin, 2005]

N u c lea tio n B u rs t o n 10 /6 /01

10

2

4

6

8100

2

4

Dp

(nm

)

280.0279.8279.6279.4279.2279.0

Day

dN/dlog(Dp) (cm-3

)

80006000400020000[Lunden et al., 2006]

FINE PARTICLE GROWTH AT BLODGETT FOREST“Banana Plot”

GAS/PARTICLE PARTITIONING THEORY

A1,A2,...,An

VOC + oxidant P1, P2, …Pn

G1, G2, …Gn

AbsorptivePartitioning Theory

,0

iom i o

i i om i

A RTK

G M p MW

M0 = pre-existing OC aerosol

R=gas constant; T=temperature; p0i = vapour pressure, MWom=molecular weight of

aerosols; i=activity coefficient in organic phase

[Pankow, 1994]

Isoprene (C5H8)

Monoterpenes(C10H1

6)

Sesquiterpenes (C15H24)

WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?

Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller)

Three factors:1. Atmospheric Abundance2. Chemical reactivity3. The vapour pressure (or

volatility) of its products

COMPARING SOA POTENTIALS

Species Global (Tg/yr)

AromaticsBenzeneTolueneXyleneOther

21.75.86.74.54.7

SOA pot’l (15%) 3.2

Monoterpenes 130.6

SOA pot’l (10%) 13.1

Sesquiterpenes ?

SOA pot’l (75%) ?

Isoprene 341

SOA pot’l (3%) 10.2

EDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes)

0MY

HC

Terpenoids: Griffin et al., 1999:Photo-oxidation: Y=1.6-84.5%NO3 oxidation: Y=12.5-89.1%O3 oxidation: Y=0-18.6%Isoprene: Kroll et al., 2005Photo-oxidation (OH): Y=0.9-3%Aromatics: Ng et al., 2007High NOx: Y=4-28%Low NOx: Y=30-36%

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated

global budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

MODELING SOA: EXPLICIT CHEMISTRY(APPROACH #1)

• Using mechanistic description of chemistry coupled to partitioning. • Captures hundreds of species and reactions (e.g. Master Chemical Mechanism, Leeds). • Often reactions and rates have not been measured but are extrapolated from known chemistry (by analogy).

These authors previously found that they needed to increases partitioning by a factor of 5-80 with the MCM to match aromatic SOA

formation at the EUPHORE chamber [Johnson et al., 2004; 2005].

[Johnson et al., 2006]

To get this agreement:1.Add 0.7 µg/m3 bkgd2.Increase partitioning coefficients by factor of 500

Example: TORCH 2003 campaign in rural UK

MODELING SOA: 2-PRODUCT MODEL(APPROACH #2)

• Unknown products, so lump products into 1=high volatility and 2=low volatility• Fit yields/partitioning parameters (’s K’s) from smog chamber observations•Used in most global/regional models

Example: Global budget of biogenic SOA

SOA parameterization (reversible partitioning)

VOCi + OXIDANTj i,jP1i,j + i,jP2i,j

Ai,j

GGi,ji,j

Pi,jEquilibrium (Komi,j) also f(POA)

[Chung and Seinfeld, 2002]

SOA from monoterpenes, sesquiterpenes and OVOCs estimated to contribute ~15% of OA burden

MODELING SOA: VOLATILITY BASIS SET(APPROACH #3)

• Expand the 2-product model to consider many volatility “bins”• Allows chemistry/physics to move organic matter along a continuum physically attractive • Loss of chemical identity complicates estimates of “mean molecular weights” and radiative forcing

Example: PMCAMx (summer 2001)

C* = saturation vapour pressure

volatility

[Donahue et al., 2005] [Lane et al., 2008]

CURRENT ESTIMATES: GLOBAL BUDGETS OF SOA

[Heald et al., 2008]

  SOA Production

  Tg yr-1

Isoprene 14.4

Monoterpenes 8.7

Sesquiterpenes 2.1

OVOC 1.6

Aromatics 3.5

TOTAL 30.3

POA Emission: 50-100 Tg yr-1

SOA ~ 25-50% of OA source in models(mostly biogenic)

Annual mean zonal distribution of SOA (2000)

GEOS-Chem model global annual budget

[Henze et al., 2008]

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated global

budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

POLLEN

BACTERIA VIRUSES

FUNGUS

ALGAEPLANTDEBRIS

Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr)

May act as CCN and IN [Diehl et al., 2001; Bauer et al., 2003; Christiner et al., 2008]

PBAP: PRESENT-THROUGHOUT THE YEAR, IN URBAN AND RURAL LOCATIONS

Mainz, Germany (1990-1998)

Lake Baikal, Russia (1996-1997)

Particles > 0.2 m, stained with protein dye

No clear seasonality: multiple PBAP sources

PBAP # fraction = 5-50%

[Jaenicke, 2005]

PBAP: PARTICLES ACROSS THE SIZE RANGE

1.0E-2

1.0E-1

1.0E+0

1.0E+1

1.0E-1 1.0E+0 1.0E+1 1.0E+2

Diameter d , µm

dV

/dlo

gd, µ

m3 /c

m3

0%20%

40%60%

80%100%120%

140%160%

180%200%

Total

Cellular

Fraction

From Andi Andreae (unpublished data)

Dominates the coarse mode (pollens, debris, etc)

May also make important

contribution to fine mode

aerosol

MARINE PBAP

[O’Dowd et al., 2008]

Primary marine aerosol from “bubble bursting mechanism” associated with sea

spray, correlated with periods of biological activity.

Chlorophyll A

Mace Head, Ireland

Ocean

Surfactant Layer (with Organics)

WINDSea-spray emissionof sea salt (and OC)

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated global

budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

WHAT MIGHT DRIVE PBAP EMISSIONS/CONCENTRATIONS?

1. Wind

2. Temperature

3. Biological activity

4. Vegetation cover

5. Humidity / wetness

6. Anthropogenic Activity

Atmospheric release/dispersion

Can affect release (surface bonding), proxy for growing season?

Stimulates source

Source = vegetation, soil, decaying matter

Facilitates release (e.g. spores)

Industrial/municipal facilities e.g. spores/molds in old buildings, sewage treatment plants, textile mills

[Jones and Harrison, 2004]

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated global

budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

MEASURING OC IN THE ATMOSPHERE

Ambient AirDenuder to

remove gas-phaseorganics

Quartz Filter (#1)

Backup (#2)(to capture OC

evaporated from filter #1)

Hamilton et al. [2004]: over 10 000 organic compounds detected in a single PM2.5 sample collected in London, England

Thermal Optical analysis to determine

OC Concentration

CHALLENGE: To measure suite of compounds classified as organic carbon, without artifacts from the gas phase

INTERPRETING ORGANIC AEROSOL MEASUREMENTS

Example from Pittsburg Air Quality Study [Cabada et al., 2004]

EC/OC ratio for primaryemissions are well-correlated(triangles).

Deviations from the slopeare indicative of a secondaryOC source (squares).

Uncertainties:• changing EC/OC emission ratios for sources• mixing of air masses

EC=elemental carbon (direct emission only, primarily fossil fuel)

CHALLENGE: once OA measured, can we separate POA and SOA?

INTERPRETING ORGANIC AEROSOL MEASUREMENTSAEROSOL MASS SPECTROMETER (AMS)

Reduce complexity of observed spectra to 2 signals:

[Zhang et al., 2005]

~2/3 of OC is SOA (in urban site!)

m/z 44: oxygenated organic aerosol

SOA

m/z 57: hydrocarbonlike organic aerosol

POA

Emitted

Escaped

Reacted + O3

+ OH

+ O3

+ O3

Oxidation Products

Above-Canopy Flux Measurements

Branch Enclosures:

Actual Emissions

Oxidation Experiments & In-Canopy Gradient

O

SCALES OF MEASUREMENT

Courtesy: Anita Lee (Berkeley, now EPA)

DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS

[Volkamer et al., 2006]

1. Measurements are challenging, cannot distinguish POA & SOA, issues such as collection efficiencies, artifacts can be important.

2. Models are simplified treatments (e.g. 2 product model)3. Models are based on lab data (applicability to ambient conditions?)

TOPICS FOR TODAY

1. What are secondary organic aerosol?

2. How do we model SOA? What are the estimated global

budgets?

3. What are primary biological aerosol particles?

4. What do we think drives these emissions?

5. What are the challenges in understanding biogenic

organic aerosol budgets?

6. How might SOA and PBAP be affected by climate

change?

CloudProcessing

HOW MIGHT BIOGENIC OA CHANGE IN THE FUTURE?

Semi-Volatiles

Oxidation by OH, O3, NO3

Direct Emission

Fossil Fuel Biomass Burning

MonoterpenesSesquiterpenes

Nucleation or ReversibleCondensation

Aromatics Isoprene

Secondary

Organic

Aerosol

Primary

Organic

Aerosol

T, Mo

PLUS: FEEDBACKS ON THE BIOSPHERE

Changing aerosol burden affects clouds/precip/chemical deposition and radiation changing SOA sources (BVOC)

Change in Emissions: -4510 g m-2 h-1

to 5174 g m-2 h-1

Christine Wiedinmyer, NCAR