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 SOA in smog chambers Detailed SOA box modelsParameter models Atmospheric aerosols Aerosol in Global models ??? Explicit models too large, many model uncertainties

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

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 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, O 3 and NO 3 Oxidation products react with OH or photolyse (now also in aerosol phase)

Model performance: Photo-oxidation two low-NO x experiments (Ng et al. 2007) most SOA yields within factor 2

10-product parameter model 5 scenarios: ◦ OH (low and high-NO x ) ◦ O 3 (low and high-NO x ) ◦ NO 3 (high-NO x ) Products fit to full model simulations with aging Diurnal cycle for VOC, OH, HO 2 and O 3 ; deposition SOA equilibrium after 12 days

Two-product model parameterizations Odum (1996) Y : SOA mass yield M 0 : absorbing organic mass α i : mass stoichiometric coefficient of product i K i : Pankow (1994) absorption equilibrium constant

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

10-product model parameters scenarioproduct m 3 µ g -1 kJ mol -1 α-pinene + OH, low NOx α-pinene + OH, high NOx α-pinene + O 3, low NOx α-pinene + O 3, high NOx α-pinene + NO 3 high NOx Reactions

10-product model curves at 298K More SOA in low-NO x than in high-NO x (factor 8 difference) α -pinene + OH leads to more SOA than α -pinene + O 3

Why more SOA in low than high-NO x ? High-NO x Low-NO x Hydroperoxides (condensable) Peroxy acyl nitrates nitrates More decompositions More volatile products

Verification at intermediate NO x 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 HO 2

Comparison with other parameterizations Low-NO x : 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-NO x : similar to Presto et al. (2005) T = 298 K

Water uptake Parameterizations were obtained for dry conditions Water uptake ◦ 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) Images No water Images With water Henze et al. (2008) Tsigarid is (2007) Pye et al. (2010) Farina et al. (2010) Monoterpenes Sesquiterpenes Isoprene Aromatics *1.6 Dicarbonyls Total SOA POA source* *81 SOA burden(Tg) Lifetime (days)

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

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-NO x 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 ( 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 + O 3 and pinonaldehyde chemistry