Aerosol water parameterization: long-term evaluation and importance for climate studies

摘要

We scrutinize the importance of aerosol water for the aerosol optical depth(AOD) calculations using a long-term evaluation of the EQuilibriumSimplified Aerosol Model v4 for climate modeling. EQSAM4clim isbased on a single solute coefficient approach that efficiently parameterizeshygroscopic growth, accounting for aerosol water uptake from thedeliquescence relative humidity up to supersaturation. EQSAM4clim extends thesingle solute coefficient approach to treat water uptake of multicomponentmixtures. The gas–aerosol partitioning and the mixed-solution water uptakecan be solved analytically, preventing the need for iterations, which iscomputationally efficient. EQSAM4clim has been implemented in the globalchemistry climate model EMAC and compared to ISORROPIA II on climatetimescales. Our global modeling results show that (I) our EMAC results of theAOD are comparable to modeling results that have been independently evaluatedfor the period 2000–2010, (II) the results of various aerosol properties ofEQSAM4clim and ISORROPIA II are similar and in agreement with AERONET andEMEP observations for the period 2000–2013, and (III) the underlyingassumptions on the aerosol water uptake limitations are important for derivedAOD calculations. Sensitivity studies of different levels of chemical agingand associated water uptake show larger effects on AOD calculations for theyear 2005 compared to the differences associated with the application of thetwo gas–liquid–solid partitioning schemes. Overall, our study demonstratesthe importance of aerosol water for climate studies.