Parameterization of Global Monoterpene SOA formation and Water Uptake, Based on a Near-explicit Mechanism Karl Ceulemans – Jean-François Müller – Steven Compernolle – Jenny Stavrakou Belgian Institute for Space Aeronomy, Brussels, Belgium ACM Conference, Davis, 2010

Secondary Organic Aerosol modeling Atmospheric aerosols SOA in smog chambers ??? Explicit models too large, many model uncertainties Detailed SOA box models Parameter models Aerosol in Global models

Do smog chambers represent atmospheric SOA well? Photochemical aging? ?? = Atmospheric aerosols SOA in smog chambers +OH Parameter model + online aging scheme Parameters from box model simulations Detailed SOA box models Aerosol in Global models

Outline BOREAM: Near-explicit model for α-pinene SOA 10-product model parameterization including aging Water uptake Global modelling

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)

Model performance: Photo-oxidation two low-NOx experiments (Ng et al. 2007) 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 aging 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 aging 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

Water uptake Parameterizations were obtained for dry conditions increases molecule number absorbing phase more condensation organic compounds Non-ideality effects Activity coefficients correct for non-ideality

Fitted activity coefficients against BOREAM , (impact water non-ideality on organic fraction)

Impact of water uptake on SOA Significant increase of SOA due to water Good agreement between full and parameter model Constant activity coefficients cause errors at high RH

Global Modeling Using global CTM IMAGESv2 (Stavrakou et al. 2009) Parameter model α-pinene used for SOA from all monoterpenes Other types of Organic Aerosol: Isoprene: Henze and Seinfeld (2006) Sesquiterpenes: Griffin et al.(1999) Aromatics: Henze et al. (2008) Small dicarbonyls (cloud processing and aqueous aerosol): Stavrakou et al. (2009) POA: non-volatile (Bond et al. 2004, Van der Werf et al. 2006)

Results U Global SOA production (Tg/year) Monoterpenes 18.8 20.7 8.7 Images No water ImagesWith water Henze et al. (2008) Tsigaridis (2007) Pye et al. (2010) Farina (2010) Monoterpenes 18.8 20.7 8.7 12.1 13.7 17.2 Sesquiterpenes 8.2 11.0 2.1 3.9 Isoprene 35.6 49.5 14.4 4.6 7.9 6.5 Aromatics 3.8 4.0 3.5 1.8 8.5* 1.6 Dicarbonyls 33.2 34.0 Total SOA 100 119 30 19 30.1 28.9 POA source* 62 70 44 39.2* 81 SOA burden(Tg) 1.75 2.12 0.81 0.82 0.54 Lifetime (days) 6.4 9.8 16.1 6.8

Global model results (July 2004) Total OA (μg m-3) Total SOA (μg m-3) Monoterpene SOA (μg m-3) fraction of total OA (%)

Modeled impact of water uptake on surface OA concentratios

Results Comparisons with observations: U.S. too large seasonal variation of OC in Eastern US MEGAN emissions might be overestimated by a factor of 2 in Eastern US (Warneke et al., 2010; Stavrakou et al., 2010) water uptake: mostly associated with isoprene SOA, highly uncertain

Comparisons with observations (cont.)

Summary 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 Global modeling with IMAGESv2 Higher SOA than in most previous studies (100-119 Tg/a) Monoterpenes : 20 Tg/a Water uptake significantly increases SOA Agreement over US: reasonable, but underestimations in winter Still wide spread in SOA for global models

Thank you for your attention!

α-pinene + O3 and pinonaldehyde chemistry