Evaluation of the atmospheric significance of multiphase reactions in atmospheric secondary organic aerosol formation

[摘要] In a simple conceptual cloud-aerosol model the mass of secondary organicaerosol (SOA) that may be formed in multiphase reaction in an idealizedscenario involving two cloud cycles separated with a cloud-free period isevaluated. The conditions are set to those typical of continental clouds,and each parameter used in the model calculations is selected as a mean ofavailable observational data of individual species for which the multiphaseSOA formation route has been established. In the idealized setting gas andaqueous-phase reactions are both considered, but only the latter is expectedto yield products of sufficiently low volatility to be retained by aerosolparticles after the cloud dissipates. The key variable of the model is theHenry-constant which primarily determines how important multiphase reactionsare relative to gas-phase photooxidation processes. The precursor consideredin the model is assumed to already have some affinity to water, i.e. it is acompound having oxygen-containing functional group(s). As a principal modeloutput an aerosol yield parameter is calculated for the multiphase SOAformation route as a function of the Henry-constant, and has been found tobe significant already above H~10³ M atm^-1. Among thepotential precursors that may be eligible for this mechanism based on theirHenry constants, there are a suite of oxygenated compounds such as primaryoxidation products of biogenic and anthropogenic hydrocarbons, including,for example, pinonaldehyde. Finally, the analogy of multiphase SOA formationto in-cloud sulfate production is exploited.

[学科分类] 大气科学