ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosols

摘要

This study presents ISORROPIA II, a thermodynamic equilibrium model for theK–Ca–Mg–NH–Na–SO–NO–Cl–HO aerosol system. Acomprehensive evaluation of its performance is conducted against wateruptake measurements for laboratory aerosol and predictions of the SCAPE2thermodynamic module over a wide range of atmospherically relevantconditions. The two models agree well, to within 13% for aerosolwater content and total PM mass, 16% for aerosol nitrate and 6% foraerosol chloride and ammonium. Largest discrepancies were found underconditions of low RH, primarily from differences in the treatment of wateruptake and solid state composition. In terms of computational speed,ISORROPIA II was more than an order of magnitude fasterthan SCAPE2, with robust and rapid convergence under all conditions. Theaddition of crustal species does not slow down the thermodynamiccalculations (compared to the older ISORROPIA code) because of optimizationsin the activity coefficient calculation algorithm. Based on itscomputational rigor and performance, ISORROPIA II appears to be a highlyattractive alternative for use in large scale air quality and atmospherictransport models.