Abstract
Abstract. The sensitivity of the formation of secondary organic aerosol (SOA) to the estimated vapour pressures of the condensable oxidation products is explored. A highly detailed reaction scheme was generated for α-pinene photooxidation using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). Vapour pressures (Pvap) were estimated with three commonly used structure activity relationships. The values of Pvap were compared for the set of secondary species generated by GECKO-A to describe α-pinene oxidation. Discrepancies in the predicted vapour pressures were found to increase with the number of functional groups borne by the species. For semi-volatile organic compounds (i.e. organic species of interest for SOA formation), differences in the predicted Pvap range between a factor of 5 to 200 on average. The simulated SOA concentrations were compared to SOA observations in the Caltech chamber during three experiments performed under a range of NOx conditions. While the model captures the qualitative features of SOA formation for the chamber experiments, SOA concentrations are systematically overestimated. For the conditions simulated, the modelled SOA speciation appears to be rather insensitive to the Pvap estimation method.
Highlights
Secondary organic aerosols have a substantial impact on human health, visibility and climate (e.g. Hallquist et al, 2009)
Vapour pressures estimated with JR/MY, NAN/NAN and SIM were compared for the set of secondary species generated by GECKO-A to describe α-pinene oxidation, i.e. for about 1.2 × 105 stable species
We present detailed simulations of secondary organic aerosol (SOA) formation from αpinene photooxidation using GECKO-A with three Vapour pressures (P vap) estimation methods: the Myrdal and Yalkowsky, Nannoolal and SIMPOL methods
Summary
Secondary organic aerosols have a substantial impact on human health, visibility and climate (e.g. Hallquist et al, 2009). – species having a vapour pressure above 10−5 atm These species will be mostly in the gas phase (ξiaer < 0.01) even for a high aerosol concentration (100 μg m−3). This category can be considered as volatile under atmospheric conditions. A detailed model describing SOA formation needs vapour pressure data for each secondary organic species produced during gas-phase oxidation. The JR/MY method was shown to provide good estimates of P vap for a set of organic species of interest for SOA formation (Camredon and Aumont, 2006).
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