Investigative modeling of new pathways for secondary organic aerosol formation
Recent advances in secondary organic aerosol (SOA) research are reviewed\nand the status of current understanding is investigated using a box\nmodel of SOA formation. Benzene and isoprene are newly identified\nprecursors that are included in this SOA model; these precursors\nform SOA via secondary products. The model is also extended to include\nsome representation of aqueous partitioning and the formation of\nhigh molecular weight products via oligomerization. Experimental\ndata and empirical relationships are used where possible, because\na detailed representation of SOA formation is not supported by the\ncurrent state of information. Sensitivity studies are conducted with\nthe SOA model and SOA predictions are found to be very sensitive\nto the treatment of the interactions between particulate water and\norganic compounds. While uncertainties due to model formulation are\nsignificant, influential model parameters include the aerosol partitioning\nratios for several small products of isoprene and the partitioning\nconstants for unidentified products (currently, the partitioning\nconstants are derived by fitting experimental data). The pH value\nused as the reference for the activation of oligomerization is also\na critical parameter. Recommendations for future work needed to improve\nSOA models include the elucidation of the water-organic relationship,\nthe extent of phase separation, and laboratory experiments conducted\nunder conditions more relevant to ambient studies (e.g., lower concentrations,\nhigher relative humidity).