Modeling Aerosol Phase Transitions and Radiative Effects

Sulfate aerosols are one of the most important types of anthropogenic aerosols in the atmosphere. They scatter incoming solar radiation, which impacts a net cooling effect on the Earth surface. Sulfate aerosols can also affect various chemical pathways such as N₂O₅ hydrolysis. To accurately quantify the extent which sulfate aerosols affect both atmospheric chemistry and the radiative budget, knowledge of their phase is needed. For example, if aqueous these particles will grow in size at high relative humidity, thus scattering solar radiation more effectively than if they were solid.

Polynomial rules have been developed by the Martin group to characterize crystallization relative humidity (CRH) for ammonium-nitrate-sulfate as a function of X and Y, where X is the ammonium fraction of the particles chemical composition and Y is the sulfate fraction. Our work is then to implement these results into GEOS-CHEM (a 3-D chemical transport model) to characterize the state of these aerosols. Currently, we are only exploring the ammonium sulfate system but plan to address the ammonium-nitrate-sulfate system in the future.

Polynomial rules:

where CRH is the crystallization relative humidity, X is the nitrate fraction of the particle's chemical composition, and Y is the sulfate fraction. We are using these results in an ongoing project to further assess the effects of particle phase on radiative forcing and atmospheric chemistry (e.g., aqueous particles are typically 10⁴ times as reactive as crystalline particles towards heterogeneous chemical hydrolysis reactions).

People Involved

• Current Group Members

  • Jun Wang
  • Scot Martin




• Collaborators

  • Andrew Hoffmann, Daniel J. Jacob (Harvard University)

Publications

1. J. Wang, A.A. Hoffmann, R. Park, D.J. Jacob, and S.T. Martin, "Global distribution of solid and aqueous sulfate aerosols: effect of the hysteresis of particle phase transitions," Journal of Geophysical Research, 2008, 113, D11207. PDF File.

2. J. Wang, D.J. Jacob, and S.T. Martin, "Sensitivity of sulfate direct climate forcing to the hysteresis of particle phase transitions," Journal of Geophysical Research, 2008, 113, D11206. PDF File.

3. J. Wang and S.T. Martin, "Satellite characterization of urban aerosols: importance of including hygroscopicity and mixing state in the retrieval algorithms," Journal of Geophysical Research, 2007, 112, D17203. PDF File.

4. Martin, S.T., H.M. Hung, R.J. Park, D.J. Jacob, R.J.D. Spurr, K.V. Chance, and M. Chin, "Effects of the Physical State of Tropospheric Ammonium-Sulfate Nitrate Particles on Global Aerosol Direct Radiative Forcing," Atmospheric Chemistry and Physics, 2004, 4, 183-214. PDF File. Table 2 Erratum.