On the effect of the chemical composition of atmospheric aerosol particles on nucleation scavenging and the formation of a cloud interstitial aerosol

Abstract

Nucleation scavenging and the formation of a cloud interstitial aerosol (CIA) were theoretically studied in terms of the chemical composition of atmospheric aerosol particles. For this study, we used our air-parcel cloud model, which includes the entrainment of air and detailed microphysics, for determining the growth and interaction of aerosol particles and drops. Maritime and remote continental aerosol particle spectrums were used whose size distributions were superpositions of three log-normal distributions, each of a prescribed chemical composition. Our results show (1) that the CIA exhibits a size distribution with a distinctive cut-off at a specific radius of the dry as well as of the wet particle size distribution. All particles above this limiting size become activated to cloud drops and, thus, are not present in the CIA spectrum. This limiting size was found to be independent of the chemical composition of the particles and only dependent on the prevailing supersaturation. Below this specific size, the CIA spectrum becomes depleted of dry aerosol particles in a manner which does depend on their chemical composition and on the supersaturation in the air. (2) The number of aerosol particles nucleated to cloud drops depends critically on the chemical composition of the particles and on the prevailing supersaturation.

Impact of aerosol size representation on modeling aerosol‐cloud interactions

“…Recognizing the large uncertainty associated with aerosol‐cloud interactions, there are some limitations in our work and future work is needed. More realistic aerosol distributions with multiple modes and varying composition should be investigated, as the particle composition may have a strong effect on the number of particles activated [ Ahr et al , 1989]. The effect of other aerosol‐cloud interaction processes such as in‐cloud scavenging of interstitial particles, droplet coalescence, and wet removal on the evolution of aerosol size distributions has not been addressed in this work and those processes may be important.…”

A parameterization of aerosol activation 3. Sectional representation

“…Our knowledge about the aerosol activation process is summarized in text [ Pruppacher and Klett , 1997; Seinfeld and Pandis , 1998] and in numerical models having detailed treatments of aerosol activation [ Jensen and Charlson , 1984; Flossmann et al , 1985; Ahr et al , 1989; Liu and Wang , 1996; Abdul‐Razzak et al , 1998]. However, the treatment in these numerical models is too computationally demanding to be applied to global climate models.…”