Importance of Organic Aerosol

1. Simulation of Organic Aerosol Concentrations in Three-Dimensional Emissions-Based Atmospheric Models Robert Griffin Institute for the Study of Earth, Oceans, and Space University of New Hampshire EMEP Workshop on Particulate Matter Measurement & Modeling April 2004

2. Importance of Organic Aerosol Local: Slater and Dibb (2002) Global: Chung and Seinfeld (2002) National: Schell et al. (2001) Regional: Griffin et al. (2002)

3. Primary Organic Aerosols Schauer et al., 2002

4. Secondary Organic Aerosols VOC + ox  P1, P2, …Pn • G1,G2,...,Gn AQ1,AQ2,...,AQn A1,A2,...,An Partitioning Theory Henry’s Law and Dissociation Hi = giaqAQi/Gi AQi AQi-AQi2- Ai / Mo RT Kom,i = ~ Gi poL,i MWomgi (further reactions in condensed phase…)

5. Modeling SOA – Where were we? Fractional aerosol coefficient: Fixed percentage of hydrocarbon parent present is converted to SOA (Grosjean, 1992) Fixed aerosol yield: Fixed percentage of hydrocarbon parent oxidized is converted to SOA (Pandis et al., 1992) Saturation: All mass of a product in excess of a given mixing ratio is converted to SOA (Strader et al., 1999) Henry’s Law: Aqueous-phase partitioning only (Aumont et al., 2000)

6. æ ö aiKom,i ç ÷ å Y = Mo ç ÷ ç ÷ 1 + Kom,i Mo ç ÷ i ç ÷ è ø Modeling SOA – Where have we been recently? Varying yield approaches: Issues: Based on smog chambers No revolatilization Implicit ‘previous step’ assumption Debate: Incremental vs. overall aerosol yield (dDMo/dDROG) (Jiang, 2003) Lack et al., 2004

7. Modeling SOA – Where are we now? Partitioning approaches Use a and K and allow partitioning to change based on T and conditions Predict chemical products via observed stoichiometry and use observed K with kon (mass transfer) and koff (equilibrium) (Kamens and Jaoui, 2001) Pun et al., 2003* *Presents an in-depth discussion of SOA modeling uncertainties Andersson-Sköld and Simpson, 2001

8. Modeling SOA – Where are we now? Predict chemical products theoretically and predict K based on molecular properties at equilibrium (Griffin et al., 2002; Pun et al., 2002) Pun et al., 2003 Griffin et al., 2002 Issues: Largest uncertainties, highest computational burden

9. Modeling OA – Where are we going? Comparison to both observed and experimental results Internal versus external (Kleeman et al., 1997) Equilibrium versus dynamic approach (Wexler et al., 1994) Inorganic-organic interactions in the aqueous phase (Clegg et al., 2001, 2003) What about other species? n-Alkanes, PAHs (UC-Riverside) Is POA really a non-volatile, inert component? Primary SVOC partitioning? Location, location, location – Houston (UT/UH), Atlanta (GIT), New England (UNH), Asia (Iowa?), … New phenomena (Jang et al., 2002; Kalberer et al., 2004)

10. Modeling SOA – How can we use it? Pun et al., 2003 Carreras et al., 2004 (submitted) Molecular types of species in SOA Effects of emissions controls (?) Health, cloud, and climate simulations? Griffin et al., 2002

11. New Phenomenon: Acid-Catalyzed Chemistry For what parent species is it relevant? Only biogenics and aromatics? For what seeds and relative acidities is it relevant? CIT/UNC-CH/ETH-PSI Adapted from Jang et al. (2002) Czoschke and Jang, 2003

12. New Phenomenon: Acid-Catalyzed Chemistry What are the kinetic and thermodynamic parameters associated with the chemistry? Barsanti and Pankow, 2004 (in press) ***How do we represent this in a three-dimensional model?***

13. Other Needs Continued/improved characterization of gas- and particle-phase products from VOC oxidation, including identification and molecular properties Improved emissions inventories and speciation of POA (no more MUC) Investigation of isoprene chemistry – can it contribute to SOA in meaningful amounts after all? (Claeys et al., 2004)

14. Conclusions/Acknowledgments OA most difficult because of the large number of species and incomplete understanding of relevant processes General underpredictions of OA: a combination of lack of appropriate molecular properties and ignorance of heterogeneous chemistry? SVOCs? Incremental versus overall yield? We’ve come a long way but still have a long way to go: integration of most rigorous modeling approaches and improved scientific understanding while considering computational burden Thanks: John Seinfeld, Donald Dabdub, Betty Pun, and Christian Seigneur (helpful discussions) and Myoseon Jang and Jim Pankow (provision of graphics)