An analysis of four models predicting the partitioning of semivolatile inorganic aerosol components

A comparison is conducted between 3 atmospheric equilibrium models: GFEMN, ISORROPIA, SCAPE2, and SEQUILIB. While ISORROPIA, SCAPE2, and SEQUILIB simp lify the problem at hand in an effort to reduce computational rigor, GFEMN does not employ many of the simplifying assumptions used in previous models , thus allowing it to accurately predict multistage aerosol behavior and de liquescence depression. We examine model performance for representative atm ospheric environments over an extended composition, temperature, and RH dom ain and against observations in Southern California. The predictions of GFE MN, ISORROPIA, SCAPE2, and SEQUILIB are in general agreement, but the latte r 3 do not adequately reproduce multistage deliquescence behavior for multi component systems. The most notable differences in model predictions occur for H+ and aerosol water concentrations; discrepancies in predictions of ae rosol nitrate and total dry inorganic Phl concentrations are not as signifi cant. The models predict different deliquescence relative humidities for mu lticomponent systems, but for ammonia poor environments, these discrepancie s do not introduce differences in total dry inorganic PM predictions. Again st measurements taken during the Southern California Air Quality Study (SCA QS), all models qualitatively reproduce but generally underpredict aerosol nitrate concentrations. Finally, based on its overall agreement with GFEMN and its computational efficiency, ISORROPIA appears to be the model of choi ce for use in large-scale aerosol transport models. In places where crustal material comprises a significant portion of total PM, SCAPE2 is an alterna tive.