ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K + –Ca 2+ –Mg 2+ –NH 4 + –Na + –SO 4 2− –NO 3 − –Cl − –H 2 O aerosols

Abstract. This study presents ISORROPIA II, a thermodynamic equilibrium model for the K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosol system. A comprehensive evaluation of its performance is conducted against water uptake measurements for laboratory aerosol and predictions of the SCAPE2 thermodynamic module over a wide range of atmospherically relevant conditions. The two models agree well, to within 13% for aerosol water content and total PM mass, 16% for aerosol nitrate and 6% for aerosol chloride and ammonium. Largest discrepancies were found under conditions of low RH, primarily from differences in the treatment of water uptake and solid state composition. In terms of computational speed, ISORROPIA II was…

• NO
  National Oceanic and Atmospheric Administration