Parameterization of SOA formation for α- pinene , based on a detailed mechanism

1. Parameterization of SOA formation for α-pinene, based on a detailed mechanism Karl Ceulemans– Steven Compernolle – Jean-François Müller Belgian Institute for Space Aeronomy, Brussels, Belgium Eurochamp 2 Workshop, Manchester, 2011

2. Outline BOREAM: Detailed model for α-pinene SOA Simulations of smog chamber experiments 10-product model parameterization including ageing

3. BOREAM : explicit model for α-pinene SOA Gas phase reaction model withadditionalgenericchemistry and aerosol formation module 10000 reactions, 2500 compounds Using KPP solver Capouet et al. (2008), Ceulemans et al. (2010)

4. Explicit chemistry • Based on advanced theoretical calculations and SARs • Oxidation by OH, O3 and NO3 • Oxidationproductsreactwith OH or photolyse (nowalso in aerosol phase) • Vapour pressure method: Capouet & Müller (2006)

5. Genericchemistry • Semi-generic: carbonnumber and functional groups • Generic: carbonnumber, vapour pressure classes (11) and 1explicit functional group 10 carbons 1 alcohol & 2 hydroperoxide LA10HPP LX9cONO2 Implicit parent structure, withpvap,im Second generation oxidation products lumped into semi-generic and generic products

6. Smog chamber Photo-oxidation low-NOx experiments (Ng et al. 2007) α-pinene and O3 given in Valorso et al. (2011) Initial: 330 ppt NO, 330 ppt NO2 , 4 ppb O3 , blacklights α-pinene decay well-reproduced ozone : reasonable agreement, sensitive to assumptions!

7. Smog chamber Photo-oxidation: SOA evolution for Ng et al. 2007 exp. 1 (low NOx): SOA mass yields are overestimated: experimental SOA yield is 40%, BOREAM simulation: 60%

8. Smog chamber Photo-oxidation: SOA composition Molar composition for Ng et al. (2007) exp. 1 (low NOx): SOA is dominated by hydroxydihydroperoxides Particle phase chemistry of hydroperoxides?

9. Model performance: Photo-oxidation * two low-NOx experiments, (Ng et al. 2007) ; somewhat overestimated most SOA yields within factor 2

10. 10-productparameter model • 5 scenarios: • OH (low and high-NOx ) • O3 (low and high-NOx ) • NO3 (high-NOx) • Products fit to full model simulations with ageing • Diurnal cycle for VOC, OH, HO2 and O3 ; deposition • SOA equilibrium after 12 days

11. Two-product model parameterizations Odum (1996) Y : SOA mass yield M0 : absorbing organic mass αi : mass stoichiometric coefficient of product i Ki : Pankow (1994) absorption equilibrium constant

12. Temperaturedependence of parameters 0°C 30°C Absorption equilibrium constant: Stoichiometric coefficient

13. 10-product model parameters Reactions

14. 10-product model curvesat 298K More SOA in low-NOx than in high-NOx (factor 8 difference) α-pinene + OH leads to more SOA than α-pinene + O3

15. Why more SOA in lowthanhigh-NOx ? Hydroperoxides (condensable) Low-NOx High-NOx nitrates Peroxy acyl nitrates More decompositions More volatile products

16. VerificationatintermediateNOx Full model parameter model (modified)

17. Sensitivity to photolysis and oxidants Not accounting for photolysis of SOA during ageing Accumulation of condensables very high yields Not very sensitive to chosen OH or HO2

18. Comparisonwithotherparameterizations T = 298 K • Low-NOx : Yields in this study are higher than for others, • Aging impact • Very low-NO x • But, also high yields in Ng et al. (2007) • High-NOx : similar to Presto et al. (2005)

19. Summary • BOREAM simulations of smog chamber photo-oxidation: most SOA yields within factor 2 • Some overestimations for low-NOx • 10-product model fit to explicit box model BOREAM including aging • Low-NOx SOA higher than previous parameterizations based on smog chambers (impact aging) • Photolysis of compounds in aerosol phase important • EVAPORATION: New vapour pressure estimation method

20. Thankyou for your attention!

21. α-pinene + O3 and pinonaldehyde chemistry