Effect of deposition of condensable vapors on SOA

This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract The effect of dry and wet deposition of semi-volatile organic compounds (SVOC) in the gas-phase on the concentrations of secondary organic aerosol (SOA) is reassessed using recently derived water solubility information. The water solubility of SVOCs was implemented as a function of their volatility distribution within the regional chemistry 5 transport model WRF-Chem, and simulations were carried out over the continental United States for the year 2010. Results show that including dry and wet removal of gas-phase SVOCs reduces annual average surface concentrations of anthropogenic and biogenic SOA by 48 % and 63 % respectively over the continental US Dry deposi-tion of gas-phase SVOCs is found to be more effective than wet deposition in reducing 10 SOA concentrations (−40 % vs. −8 % for anthropogenics, −52 % vs. −11 % for bio-genics). Reductions for biogenic SOA are found to be higher due to the higher water solubility of biogenic SVOCs. The majority of the total mass of SVOC + SOA is actually deposited via the gas-phase (61 % for anthropogenics, 76 % for biogenics). A number of sensitivity studies shows that this is a robust feature of the modeling system. 15 Other models that do not consider dry and wet removal of gas-phase SVOCs would hence overestimate SOA concentrations by roughly 50 %. Assumptions about the water solubility of SVOCs made in some current modeling systems (H * = 10 5 M atm −1 ; H * = H * (HNO 3)) still lead to an overestimation of 25 %/10 % compared to our best estimate. A saturation effect is observed for Henry's law constants above 10 8 M atm −1 , 20 suggesting an upper bound of reductions in surface level SOA concentrations by 60 % through removal of gas-phase SVOCs. Considering reactivity of gas-phase SVOCs in the dry deposition scheme was found to be negligible. Further sensitivity studies where we reduce the volatility of organic matter show that consideration of gas-phase SVOC removal still reduces average SOA concentrations by 31 % on average. We consider 25 this a lower bound for the effect of gas-phase SVOC removal on SOA concentrations.