Atmospheric Organic Aerosol: More Than Primary Emissions
Brent J. Williams
Raymond R. Tucker ICARES Career-Development Assistant ProfessorWashington University in St. Louis
Department of Energy, Environmental, & Chemical Engineering
PI: Atmospheric Chemistry & Technology (ACT) Laboratory
Mumbai: December 7, 2012
Why Do We Care: Size-dependent Health Effects
[NARSTO, 2003]
Course aerosols deposit by impaction in nose and throat.
Ultrafine aerosol deposit by diffusion deeper in lungs in smaller pathways.
Fine aerosol has a minimum in deposition efficiency at approximately 0.5 micron diameter.
Many organic species in Fine PM are classified as toxins, mutagens, and carcinogens.
IPCC-Climate Change, 2007
Radiative forcing components
Why Do We Care: Climate Effects
Changes since 1750 (preindustrial)
Not accounting for many aerosol indirect effects.
IPCC-Climate Change, 2007
• Sulfate• Primary Organic Carbon from Fossil Fuels • Black Carbon from Fossil Fuels• Biomass burning• Nitrate• Mineral Dust
IPCC-Climate Change, 2007
• Sulfate• Primary Organic Carbon from Fossil Fuels • Black Carbon from Fossil Fuels• Biomass burning• Nitrate• Mineral Dust
Not Accounting for Secondary Organic Aerosol (SOA). Is there
enough SOA to make a difference?
2 main questions to discuss today:
1) Why do we care?
2) Where does it come from?
-primary vs. secondary
Organic Aerosol
Organic Aerosol is Most Abundant Fine PM Component Globally
Zhang et al., 2007organics sulfate nitrate ammonium
Organics44%
Sulfate32%
Ammonium13%
Nitrate10%
Chloride1%
• Northern Hemisphere Average (37 studies)• More Summer data than Winter • Non-Refractory Only (doesn’t include metals and elemental carbon)• Sulfate and Nitrate are formed through secondary processes• Organics previously thought of as mostly primary emissions, but that view has changed.
Major Atmospheric Species (fine PM)
Zhang et al., Geophys Res Lett, 2007
Atmospheric Organic Matter:Oxidation state and carbon numbers
oleicacid
ethane
acetaldehydephenanthrene
sucrose levoglucosan
sesquiterpene monoterpene isoprene
C5 tetrol
CH2O
glyoxalglyoxaldimer
oxalicacid
pinonic
pinic
C8triacid
butaneoctane
toluene
CH4
CO2
CO
MVK
methylglyoxal
fulvicacid
dodecane CH3OH
elementalcarbon
Ox. State ≈ 2 (O/C) – (H/C)
Kroll, Nature Chemistry, 2011.
C40
Chemical complexity of atmospheric organics
carbonyls, alcohols, acids only
Ox. State ≈ 2 (O/C) – (H/C) C40
Ambient Mass Concentrations Decrease
Kroll, Nature Chemistry, 2011.
Oxidation state of organic aerosol
Organic aerosol is an intermediate in the oxidationof most organics to CO2
CO2
CO
C40
Kroll, Nature Chemistry, 2011.
Organic Aerosol
gas
particle
Jimenez, Canagaratna, Donahue, et al., Science, 2009
2D – Volatility Basis Set space
Illustration of SOA evolution through 2D-VBS space
Secondary Organic Aerosol (SOA) Formation: Example
- 10 days of measurements from thermal desorption aerosol gas chromatograph (TAG)- PAR = visible light
Naphthalene: C10H8 (mostly in Gas-phase)Phthalic acid: C8H6O4 (In both Gas- and Particle-phase)
Williams et al., PNAS, 2010
Fractional Time Of Day
Na
ph
tha
len
e (
ng
m-3
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
20
40
60
80
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
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20
40
60
80
Ph
tha
lic
Ac
id (
ng
m-3
)
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500
1000
1500
PA
R (
um
ole
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-2 s
-1)
Par
ticle
-Pha
se C
once
ntra
tions
Primary vs Secondary Organic Aerosol (OA)
Zhang et al., Geophys Res Lett, 2007
Effects of organic gases and organic particles can NOT be thought of as separate issues.
Secondary OA > Primary OA
Observed SOA > modeled SOALack in our fundamental knowledge of SOA formation and transformation.At least partially due to lack of measurements for semivolatile compounds.
Volkamer et al., Geophys Res Lett, 2006.
Major discrepancy between measured and modeled SOA
Organics make up 20-90% of fine particle mass and contain tens of thousands of compounds that can be used to determine sources and transformations (much is Secondary).
What we need to know about atmospheric organic matter:
-Physical Properties of Particles
-Chemical Properties-composition and concentrations (gases and particles)-composition transformations as air masses age
-Want to determine all sources and fate of atmospheric gases and particles.
-What effects do these particles and gases have on the environment?
-What can be done about it? (Policy and Management)
Organics44%
Sulfate32%
Ammonium13%
Nitrate10%
Chloride1%
• Northern Hemisphere Average (37 studies)• More Summer data than Winter • Non-Refractory Only (doesn’t include metals and elemental carbon)
General Speciation: AMS Speciation (PM1)
Zhang et al., Geophys Res Lett, 2007
Organics44%
Sulfate32%
Ammonium13%
Nitrate10%
Chloride1%
Low Volatility Oxygenated Organic Aerosol (LV-OOA)
x%
y%
z%Semivolatile OOA (SV-OOA)
Hydrocarbon-like OA (HOA)
• x, y, z% varies (x > y > z in urban locations, z > y > x in remote locations)• Can also provide estimate of Biomass OA, but some interference exists• Still lacks specifics on sources of OA • Specifics are crucial for Regulation and Modeling Efforts
More Specific: AMS Speciation (w/ PMF of OA)
TAG
Thermal Desorption Aerosol Gas Chromatograph (TAG)
An in-situ instrument used to study the Sources and Transformation of Organic Particulate Matter
Hourly measurements of organic aerosol molecular composition
Williams et al., Aerosol Sci Technol, 2006
More Specific Yet: TAG
1. Collection technique:– Inertial Impaction (300C)
2. Sample transfer:– Thermal Desorption (50-3000C)
3. Chemical separation:– Gas Chromatography
4. Compound identification and quantification:– Electron Impact Mass Spectrometry
Gas Chromatograph
MassSpectrometer
Heated valve
Aerosol Collector &
Thermal Desorption Cell
Cyclone Precut(PM2.5)
Humidifier(adhesion)
Filter (field blank)
x
1
2
34
Note: many particles will be internally mixed.
Factor Analysisto group compounds
15.00 20.00 25.00 30.00 35.00 40.00 45.000
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000
5000000
Time-->
Abundance
TIC: 33702-12.DTIC: 33702-13.D (*)
Various forms of Petroleum Combustion
Coffee
Residential Wood Combustion
Plant WaxesRela
tive
Abun
danc
e
Retention Time
Secondary Organic Aerosol
• Organic portion (20-90% of total mass) is helpful in determining and understanding:- Particle sources- Particle formation processes- Particle transformations
Williams et al., Aerosol Sci Technol, 2006
Organics44%
Sulfate32%
Ammonium13%
Nitrate10%
Chloride1%
• Example Sources• Positive Matrix Factorization of Molecular Marker Compounds• Multivariate fit of TAG PMF factors to total OA from AMS
Primary Vehicle EmissionsFood Cooking
Plant Waxes
Biomass Burning:Softwood
Biomass Burning:Hardwood
Pesticides
Pharmaceuticals
Anthropogenic Secondary Organic Aerosol (SOA)
Biogenic SOA: Isoprene SOA
Biogenic SOA: Terpene SOA
More Specific Yet: TAG Speciation(scaling to AMS OA mass)
Plasticizers
Further Aged Anthro-SOA
Los Angeles Riverside
N
80 km
San Diego
135 km
PM2.5 Gridded Emissions (short tons/ozone season day/grid cell)
Williams et al., Atmos Chem Phys Discuss, 2010
Example TAG Field Study:Study of Organic Aerosol at Riverside (SOAR)
• Use hundreds of TAG compound timelines in Positive Matrix Factorization (PMF)• Determine major OA components (sources)• Scale TAG factors to AMS OA mass
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TAG’s 1-hour time resolution provides diurnal trends
Main methods to determine particle sources:
Chemical Mass Balance:
Factor Analysis (e.g., Positive Matrix Factorization):
cik= concentration of chemical species i in the fine particles at receptor site kaij = relative concentration of species i in the fine particle emissions from source jsjk = increment to total fine PM concentration at receptor site k originating from source jm= # of source types
Schauer and Cass, ES&T, 2000
Ulbrich et al., Atm Chem Phys, 2009
X = concentration of chemical speciesG = Factor Profile F = Factor Time SeriesE = Residualsp = Factor#s = estimated errors (uncertainty)Q = quality of fit parameter
G and F are determined by minimizing sum of least squares between residuals and errors:
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SO
A2
SO
A3
SO
A4
+S
VR
PA
LVF
CB
BB
io
Hydrocarbon Oxygenated Biogenic N-Containing Other
Williams et al., Atmos Chem Phys Discuss, 2010
TAG PMF Components (SOAR)Biogenic Particles
Biomass Burning
Food Cooking
Local Vehicles
Regional Primary Anthropogenics
Aged SOA + Biogenic SOA
Aged SOA
Regional Fresh SOA
Local Fresh SOA
5
10
15N
S
W E
SOA
Supporting Information
Local Meteorology Backward Trajectory Modeling Correlations
RHTemp
O3
COOC/EC
gas-phase organics
AMS species
ATOFMS (single particles)
Etc.
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6.8 mg m-3
8.6
10.0
13.0
11.610.7
10.1
11.7
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9.5
0:002:00
4:00
6:00
8:00
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14:00
16:00
18:00
20:00
22:00
SOA1SOA2SOA3
SOA4+SemivolatileRegional Primary AnthropogenicLocal Vehicle
Food CookingBiomass BurningPrimary BiogenicMeasured OA
Williams et al., Atmos Chem Phys Discuss, 2010
TAG PMF Components (summer)
SOA1 = Local Fresh SOA
SOA2 = Regional Fresh SOA
SOA3 = Aged SOA
SOA4 = Aged SOA + Biogenic SOA
SOA~70% of fine OAImmediately downwind of large urban area
Previous Studies: SOA~20-50% of fine OA