HR: 1330h
AN: A22A-1047    [PDF]
TI: Impact of Nitric Acid on Cloud Microphysics and Climate
AU: * Xue, H
EM: huiwen.xue@noaa.gov
AF: NOAA/ETL, 325 Broadway, Boulder, CO 80305 United States
AU: Feingold, G
EM: graham.feingold@noaa.gov
AF: NOAA/ETL, 325 Broadway, Boulder, CO 80305 United States
AB: Numerical simulation of cloud formation using an adiabatic cloud parcel model indicates that cloud droplet number concentration can be significantly increased when soluble trace gases, such as nitric acid, are present in the atmosphere. The increased number of cloud droplets may enhance the indirect climate forcing by aerosol. The growth of haze and cloud droplets by condensing water and nitric acid vapors on ammonium sulfate particles has been calculated explicitly using a kinetic droplet growth model. Results show that the effect of nitric acid is most significant when the updraft is weak. Because the transfer of water and nitric acid vapors to the growing droplets is a rate-limiting factor, we also investigated the sensitivity of cloud droplet number to different mass accommodation coefficients of water and nitric acid. It is found that for both water and nitric acid smaller mass accommodation coefficients can lead to more cloud droplets, including those that do not grow spontaneously but are large enough to have radiative effects. This is due to the fact that the partitioning of nitric acid among the gas and liquid phases depends on the number and sizes of the cloud droplets. Some of the cloud droplets may evaporate even after activation in a complex binary condensation and evaporation process. When the mass accommodation coefficients are small, the deactivation process becomes very slow and the droplets can remain large enough, and for sufficiently long enough, to have a radiative effect. We will present results that evaluate the importance of kinetic limitations on the transfer of soluble trace gases and explore the extent to which these affect aerosol indirect forcing on climate.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting