1. BIOGENIC AEROSOL: SECONDARY ORGANIC AEROSOL (SOA) PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)

2. THE IMPORTANCE OF ORGANIC AEROSOL
Sulfate Organics
[Zhang et al., 2007]
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]

3. ORGANIC CARBON AEROSOL
Secondary
Organic
Aerosol
Cloud
Processing
Semi-
Volatiles
Nucleation or
ReversibleCondensation
Primary
Organic
Aerosol
Oxidation
by OH, O3,
NO3
Monoterpenes
Sesquiterpenes
Aromatics
Isoprene
Direct
Emission
Fossil Fuel Biomass
Burning

4. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

5. SECONDARY ORGANIC AEROSOL PRODUCTION
VOC Emissions
Nucleation
(oxidation products)
Oxidation Reactions
(OH, O3,NO3)
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]

6. FINE PARTICLE GROWTH AT BLODGETT FOREST
“Banana Plot”
[Lunden et al., 2006]

7. GAS/PARTICLE PARTITIONING THEORY
VOC + oxidant  P1, P2, …Pn
M0 = pre-existing
OC aerosol
A1,A2,...,An
G1, G2, …Gn
Absorptive
Partitioning Theory
[Pankow, 1994]
R=gas constant; T=temperature; p0i = vapour pressure, MWom=molecular weight of aerosols; i=activity coefficient in organic phase

8. WHICH VOC’s ARE IMPORTANT SOA PRECURSORS?
Isoprene (C5H8)
Three factors:
Atmospheric Abundance
Chemical reactivity
The vapour pressure (or volatility) of its products
Monoterpenes(C10H16)
Sesquiterpenes (C15H24)
Anthropogenic SOA-precursors = aromatics (emissions are 10x smaller)

9. COMPARING SOA POTENTIALS
EDGAR 1990 Emissions (Aromatics) and GEIA (Isoprene/Monoterpenes)
Species
Global (Tg/yr)
Aromatics
Benzene
Toluene
Xylene
Other
21.7
5.8
6.7
4.5
4.7
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
Terpenoids: Griffin et al., 1999:
Photo-oxidation: Y= %
NO3 oxidation: Y= %
O3 oxidation: Y=0-18.6%
Isoprene: Kroll et al., 2005
Photo-oxidation (OH): Y=0.9-3%
Aromatics: Ng et al., 2007
High NOx: Y=4-28%
Low NOx: Y=30-36%

10. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

11. 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).
Example: TORCH 2003 campaign in rural UK
To get this agreement:
Add 0.7 µg/m3 bkgd
Increase partitioning coefficients by factor of 500
[Johnson et al., 2006]
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].

12. MODELING SOA: 2-PRODUCT MODEL (APPROACH #2)
Unknown products, so lump products into 1=high volatility and 2=low volatility
Fit yields/partitioning parameters (a’s K’s) from smog chamber observations
Used in most global/regional models
SOA parameterization (reversible partitioning)
VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
Ai,j
Gi,j
Pi,j
Equilibrium (Komi,j)
 also f(POA)
Example: Global budget of biogenic SOA
SOA from monoterpenes, sesquiterpenes and OVOCs estimated to contribute ~15% of OA burden
[Chung and Seinfeld, 2002]

13. 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)
volatility
C* = saturation vapour pressure
[Donahue et al., 2005]
[Lane et al., 2008]

14. CURRENT ESTIMATES: GLOBAL BUDGETS OF SOA
Annual mean zonal distribution of SOA (2000)
[Heald et al., 2008]
GEOS-Chem model global annual budget
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: Tg yr-1
SOA ~ 25-50% of OA source in models
(mostly biogenic)
[Henze et al., 2008]

15. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

16. PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
BACTERIA
VIRUSES
POLLEN
FUNGUS
PLANT
DEBRIS
ALGAE
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]

17. PBAP: PRESENT-THROUGHOUT THE YEAR, IN URBAN AND RURAL LOCATIONS
Mainz, Germany ( )
Particles > 0.2 m, stained with protein dye
No clear seasonality: multiple PBAP sources
PBAP # fraction = 5-50%
Lake Baikal, Russia ( )
[Jaenicke, 2005]

18. PBAP: PARTICLES ACROSS THE SIZE RANGE
May also make important contribution to fine mode aerosol
Dominates the coarse mode (pollens, debris, etc)
From Andi Andreae (unpublished data)

19. Surfactant Layer (with Organics)
MARINE PBAP
Sea-spray emission
of sea salt (and OC)
WIND
Primary marine aerosol from “bubble bursting mechanism” associated with sea spray, correlated with periods of biological activity.
Surfactant Layer (with Organics)
Ocean
Mace Head, Ireland
Chlorophyll A
[O’Dowd et al., 2008]

20. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

21. WHAT MIGHT DRIVE PBAP EMISSIONS/CONCENTRATIONS?
Wind
Temperature
Biological activity
Vegetation cover
Humidity / wetness
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]

22. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

23. MEASURING OC IN THE ATMOSPHERE
Hamilton et al. [2004]: over organic compounds detected in a single PM2.5 sample collected in London, England
CHALLENGE: To measure suite of compounds classified as organic carbon, without artifacts from the gas phase
Ambient Air
Denuder to
remove gas-phase
organics
Quartz
Filter (#1)
Backup (#2)
(to capture OC
evaporated from
filter #1)
Thermal Optical
analysis to determine OC Concentration

24. INTERPRETING ORGANIC AEROSOL MEASUREMENTS
CHALLENGE: once OA measured, can we separate POA and SOA?
Example from Pittsburg Air Quality Study [Cabada et al., 2004]
EC/OC ratio for primary
emissions are well-correlated
(triangles).
Deviations from the slope
are indicative of a secondary
OC source (squares).
Uncertainties:
changing EC/OC emission ratios for sources
mixing of air masses
EC=elemental carbon (direct emission only, primarily fossil fuel)

25. Reduce complexity of observed spectra to 2 signals:
INTERPRETING ORGANIC AEROSOL MEASUREMENTS AEROSOL MASS SPECTROMETER (AMS)
m/z 57: hydrocarbon
like organic aerosol
 POA
m/z 44: oxygenated
organic aerosol
 SOA
Reduce complexity of observed spectra to 2 signals:
~2/3 of OC is SOA
(in urban site!)
[Zhang et al., 2005]

26. SCALES OF MEASUREMENT Escaped Reacted Emitted
Above-Canopy Flux Measurements
Escaped
+ O3
+ OH
Oxidation Experiments & In-Canopy Gradient
Oxidation Products
Reacted
Emitted
Branch Enclosures: Actual Emissions
Courtesy: Anita Lee (Berkeley, now EPA)

27. DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS
Measurements are challenging, cannot distinguish POA & SOA, issues such as collection efficiencies, artifacts can be important.
Models are simplified treatments (e.g. 2 product model)
Models are based on lab data (applicability to ambient conditions?)
[Volkamer et al., 2006]

28. TOPICS FOR TODAY What are secondary organic aerosol?
How do we model SOA? What are the estimated global budgets?
What are primary biological aerosol particles?
What do we think drives these emissions?
What are the challenges in understanding biogenic organic aerosol budgets?
How might SOA and PBAP be affected by climate change?

30. HOW MIGHT BIOGENIC OA CHANGE IN THE FUTURE?
Secondary
Organic
Aerosol
Cloud
Processing
Semi-
Volatiles
Nucleation or
ReversibleCondensation
Primary
Organic
Aerosol
Oxidation
by OH, O3,
NO3
T, Mo
Monoterpenes
Sesquiterpenes
Aromatics
Isoprene
Direct
Emission
Fossil Fuel Biomass
Burning

31. PLUS: FEEDBACKS ON THE BIOSPHERE
Changing aerosol burden affects clouds/precip/chemical deposition and radiation  changing SOA sources (BVOC)
Change in Emissions:
-4510 mg m-2 h-1 to
5174 mg m-2 h-1
Christine Wiedinmyer, NCAR