Dr. Jun Wang

Global modeling of aerosol phase transition and

its  implication to visibility, radiative forcing and cirrus cloud formation
 

References:

Wang, J.,  D. J. Jacob, and S. T. Martin, Sensitivity of sulfate direct climate forcing to the hysteresis of particle phase transitions, J. Geophys. Res., submitted.

1. Motivation

A fine particle in ambient air can be in either solid or liquid phase, depending on the composition and the relative humidity (RH) back-trajectory of that particle. For instance, a dry ammonium sulfate particle exposed to increasing RH becomes aqueous at 80% RH (i.e., DRH) and subsequently grows at higher RH by condensation of water vapor. If it is then exposed to decreasing RH, it gradually shrinks but does not become solid until 35% RH (i.e., CRH). Hence, between 35% and 80% RH, the ammonium sulfate particle  can be either in solid or liquid phase, depending which branch of the hysteresis loop this particle followed.

In many climate and air quality models, the sulfate phase is not  modeled because of the difficulties in tracking the particle RH trajectory. In this project, using GEOS-Chem and the CRH data measured in the lab, we developed methods of explicitly modeling the aerosol phase transition, and quantitatively investigate its implications to aerosol forcing, visibility, cirrus cloud formation, and heterogeneous chemistry.

2. Result

We have so far completed the modeling of sulfate phase transition in sulfate-water system. Please see details in our manuscript. We are now looking into the sulfate phase impact on cirrus formation.

The following figure shows the seasonal and geographic distributions of tropospheric sulfate burdens in aqueous and solid phases, and corresponding aerosol optical thicknesses τaq and τsd. The numbers located to the upper right of each panel show globally averaged quantities.