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

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

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

Explicit chemistry Based on advanced theoretical calculations and SARs Oxidation by OH, O3 and NO3 Oxidation products react with OH or photolyse (now also in aerosol phase) Vapour pressure method: Capouet & Müller (2006)

Generic chemistry Semi-generic: carbon number and functional groups Generic: carbon number, vapour pressure classes (11) and 1explicit functional group Second generation oxidation products lumped into semi- generic and generic products 10 carbons 1 alcohol & 2 hydroperoxide LA10HPP LX9cONO2 Implicit parent structure, with pvap,im

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!

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%

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

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

10-product parameter 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

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

Temperature dependence of parameters Absorption equilibrium constant: Stoichiometric coefficient 0°C 30°C

10-product model parameters scenario product m3 µg-1 kJ mol-1 α-pinene + OH, low NOx 1 0.307 -0.022 6.98 85.6 2 0.211 -0.0135 0.117 22.2 α-pinene + OH, high NOx 3 0.028 -0.040 0.762 132.2 4 0.109 -0.025 0.00486 85.3 α-pinene + O3, low NOx 5 0.282 -0.0132 4.155 86.8 6 0.142 0.0158 77.1 α-pinene + O3, high NOx 7 0.016 -0.057 0.837 161.8 8 0.213 -0.0054 0.00326 111.4 α-pinene + NO3 high NOx 9 0.018 -0.049 0.493 172.4 10 0.251 -0.015 0.00092 147.6 Reactions

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

Why more SOA in low than high-NOx ? Hydroperoxides (condensable) Low-NOx High-NOx nitrates Peroxy acyl nitrates More decompositions More volatile products

Verification at intermediate NOx Full model parameter model (modified)

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

Comparison with other parameterizations 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) T = 298 K

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

Thank you for your attention!

α-pinene + O3 and pinonaldehyde chemistry