The Importance of the Chemical and Physical Properties of Aerosols in Determining Their Transport and Residence Times in the Troposphere

Abstract

Tropospheric aerosols are now clearly identified as one of the key missing links in many aspects of climate and radiative forcing processes, as well as in the health effects of air quality. This chapter examines some basic chemical and physical properties of aerosols that determine their diffusional growth, atmospheric removal by gravitational settling, and uptake of water leading to increased size and subsequent removal by both wet and dry deposition. The importance of aerosol size and chemical compositions in determining their atmospheric lifetimes is stressed, with particular attention to combustion-derived carbonaceous soots. The atmospheric oxidation of oily soot surfaces to make these organic aerosols sufficiently hygroscopic for particle growth and atmospheric removal is expected to require a substantial time period. Mean residence times for submicron aerosols, as determined by using natural radionuclides, support the observation that a significant fraction of fine aerosols (0.1-1 μm) have considerably longer atmospheric lifetimes than anticipated from normal washout and dry depositional processes of hygroscopic aerosols. It is concluded that the surface and chemical properties of aerosols and particulate matter must be accounted for in both climate effects and assessments of health impacts of atmospheric aerosols (18).