1. Secondary Organic Aerosols
Formation
and
Characterization

2. Overview Background Formation Modeling Theoretical investigations
Chamber experiments

3. Particulate Matter in the Atmosphere
PM affects visibility, climate, health.
Inorganic fractions well characterized.
Organic fractions are poorly characterized, very complex.

4. Modeling Atmospheric Aerosol Formation
Model aerosol formation to understand its affects on air quality and climate change
Accurately represent organic fraction
Better characterization chemical composition of atmospheric organic aerosols
Better understanding of secondary organic aerosol (SOA) formation, including the role of MW-building reactions (i.e., "accretion reactions”)

5. Formation of Atmospheric Organic Aerosols
Aerosols = liquid or solid particles suspended in a gas (e.g., the atmosphere)
Physical state of compound largely dependent on pure-compound vapor pressure (p°L)
How can a compound have low/lower volatility?
Inherent: compounds emitted as PM
Undergo oxidation: VOCs + NOx,O3, •OH → oxidation products
Undergo MW-building reactions: oxidation products/ atmospheric compounds→ high-MW products
Lowering volatility increases the tendency of a compound to condense, thereby forming PM

6. Formation of Atmospheric Organic AerosolsOA
gas/particle (G/P) partitioning
gas/particle (G/P) partitioning
high molecular-weight (MW)/
low-volatility products
accretion reactions
oxidation
products
-COOH
-OH
-C=O
Biogenic
Anthropogenic
oxidation
Emissions Volatile Organic Compounds

7. Fundamental Thermodynamics of SOA Formation by Accretion Reaction
Ag + Bg Cg Cliq

8. Mathematical Solution Process
Multiple accretion reactions and products from parent compound A:
2A C1
2A C2 + H2O
A + B C3
A + B C4 + H2O
Mass balance leads to:
A and C denote concentrations (µg m-3)
N number of accretion products from A

9. Accretion Reactions of Aldehydes and Ketones
Based on work of Jang and Kamens
Reaction of 4 n-aldehydes and ketones (C4, C6, C8, C10)
5 Accretion products for each aldehyde/ketone (hydrate, dimer, trimer, hemiacetal, acetal, hydroxy carbonyl, unsaturated carbonyl)
Considered same reactions for pinonaldehyde, inputs representative of ambient conditions

10. Accretion Reactions of Dialdehydes, Methylglyoxal, Diketones

11. Accretion Reactions of Carboxylic and Dicarboxylic Acids: Ester and Amide Formation
Accretion reactions of 5 acids
Ester formation w/ MBO, amide formation w/DEA and NH3
Inputs representative of ambient conditions

12. Results for Carboxylic and Dicarboxylic Acids
Predicted OPM as a Function of A0
MBO0 and DEA0= 1 µg m-3
NH3 ≈ 0.1 µg m-3
OPMna = 10 µg m-3
RH = 20%, T = 298 K
For malic, maleic, and pinic acids OPM formation is significant
For acetic acid, accretion products do not condense into OPM phase
Esters and at least 1 amide contribute to predicted level of additional OPM

13. Implications for Observed OPM Formation in Chamber Experiments
MW g mol-1 dominant accretion reactions
MW g mol-1, combination of monomers (Tolocka et al., 2004)
MW g mol-1 dimers, MW g mol-1 trimers and higher oligomers (Gao et al., 2004a,b)
OPMna = 0, RH = 50%, T = 298 K
Δα-Pinene
(µg m-3)
Predicted OPM
6 (~1 ppb)
0.15 56
1.7
280
8.9
560 18
840 27
19000
(~3400 ppb)
650

14. Summary of Dissertation Research
Accretion reactions appear to play a role in atmospheric SOA formation
Currently, the dominant accretion reactions/products are not known
Developed a “first-cut” approach to identifying favorable reactions and estimating their potential contribution to SOA
Lot’s of work to be done!

15. Biogenic Aerosol Chamber
Reaction Chamber
Ozone Source
Cylinder Air
CIMS
PTRMS
Ozone Monitor 2
SO2 Monitor
SMPS
Filter Sampler
UFPC
HTDMA
SO2
Scrubber
Biomass Chamber
Humidifier
TDCIMS
T, RH

16. Filter Sample Analysis: GC x GC
Entire sample passed through two different columns
First column usually separates based on volatility, second usually separates based on polarity

17. GC x GC Spectrum (← ret. time) polarity volatility (→ ret. time)
alcohols
(← ret. time)
polarity
aldehydes
alkanes
volatility (→ ret. time)

18. Future Plans
Look for accretion products in filter samples from chamber experiments and field experiments
Use PTR-MS to “track” gas phase species
Use GC x GC to analyze filter samples
Compare data with thermodynamic model predictions
Parameterize reactions to include in regional/global models