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

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BIOGENIC AEROSOLSECONDARY ORGANIC AEROSOL
(SOA)PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
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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

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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
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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?

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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
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FINE PARTICLE GROWTH AT BLODGETT FOREST
Banana Plot
Lunden et al., 2006
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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
Rgas constant Ttemperature p0i vapour
pressure, MWommolecular weight of aerosols
?iactivity coefficient in organic phase
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WHICH VOCs ARE IMPORTANT SOA PRECURSORS?

• Three factors
• Atmospheric Abundance
• Chemical reactivity
• The vapour pressure (or volatility) of its
  products

Isoprene (C5H8)
Monoterpenes(C10H16)
Sesquiterpenes (C15H24)
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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 potl (15) 3.2
Monoterpenes 130.6
SOA potl (10) 13.1
Sesquiterpenes ?
SOA potl (75) ?
Isoprene 341
SOA potl (3) 10.2
Terpenoids Griffin et al., 1999 Photo-oxidation
Y1.6-84.5 NO3 oxidation Y12.5-89.1 O3
oxidation Y0-18.6 Isoprene Kroll et al.,
2005 Photo-oxidation (OH) Y0.9-3 Aromatics Ng
et al., 2007 High NOx Y4-28 Low NOx Y30-36
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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?

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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.
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MODELING SOA 2-PRODUCT MODEL(APPROACH 2)

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

Example Global budget of biogenic SOA
SOA from monoterpenes, sesquiterpenes and OVOCs
estimated to contribute 15 of OA burden
Chung and Seinfeld, 2002
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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
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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 50-100 Tg yr-1 SOA 25-50 of OA
source in models (mostly biogenic)
Henze et al., 2008
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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?

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PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP)
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
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PBAP PRESENT-THROUGHOUT THE YEAR, IN URBAN AND
RURAL LOCATIONS
Mainz, Germany (1990-1998)
Particles gt 0.2 ?m, stained with protein dye No
clear seasonality multiple PBAP sources PBAP
fraction 5-50
Lake Baikal, Russia (1996-1997)
Jaenicke, 2005
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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)
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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
ODowd et al., 2008
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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?

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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
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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?

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MEASURING OC IN THE ATMOSPHERE
Hamilton et al. 2004 over 10 000 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
Backup (2) (to capture OC evaporated from
filter 1)
Quartz Filter (1)
Thermal Optical analysis to determine OC
Concentration
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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

ECelemental carbon (direct emission only,
primarily fossil fuel)
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INTERPRETING ORGANIC AEROSOL MEASUREMENTSAEROSOL
MASS SPECTROMETER (AMS)
m/z 44 oxygenated organic aerosol ? SOA
m/z 57 hydrocarbon like organic aerosol ? POA
Reduce complexity of observed spectra to 2
signals
2/3 of OC is SOA (in urban site!)
Zhang et al., 2005
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SCALES OF MEASUREMENT
Above-Canopy Flux Measurements
Escaped
Oxidation Experiments In-Canopy Gradient
Oxidation Products
Reacted
Emitted
Branch Enclosures Actual Emissions
Courtesy Anita Lee (Berkeley, now EPA)
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DISAGREEMENT BETWEEN MODELS AND OBSERVATIONS

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?)

Volkamer et al., 2006
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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?

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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
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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