A Comparison of Water Uptake by Aerosols Using Two Thermodynamic Models
| Li Xu | University of Michigan |
| Joyce Penner | University of Michigan |
Category: Aerosols
The water uptake by hygroscopic aerosols can significantly alter aerosol size, optical properties, and direct radiative forcing. We investigate two methods to determine the uptake of water by aerosols. Thermodynamic aerosol models determine aerosol water uptake by accounting for a mixing rule, also known as the Zdanovskii-Stokes-Robsin (ZSR) relationship, which is usually solved iteratively for a given equilibrium condition. The Metzger method (Metzger and Lelieveld 2007) determines water uptake analytically (without any iteration). This yields a significant reduction of computing time. They assume the water activity is equal to the ambient relative humidity at equilibrium, and hence only use relative-humidity-dependent activity coefficients for volatile aerosol compounds. Here, we examine this new method of uptake of water by aerosols by comparing the results with those of the thermodynamic model currently used in our global chemical transport model (Feng and Penner 2007) under typical ambient conditions.
Feng, Y. and J.E. Penner, 2007: Global Modeling of Nitrate and Ammonium: Interaction of Aerosols and Tropospheric Chemistry, J. Geophys. Res., 112, D01304, doi:10.1029/2005JD006404.
Metzger, S. and J. Lelieveld, Reforming atmospheric aerosol thermodynamics and hygroscopic growth into fog, haze and clouds, Atmos, Chem. Phys, 7, 3163-3193, 2007.
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