ABSTRACT
Atmospheric aerosols exhibit significant variations in their physical, chemical, and optical characteristics. Physical characteristics such as size, spectrum, and shape are governed by their formation mechanisms, and their chemical characteristic is determined by the source(s) from which they are produced. The optical characteristics of aerosols in turn depend on the number and size, and their scattering and absorption nature. Junge was among the first scientists to have recognized the need for using logarithmic scales for the illustration of aerosol size distributions. Lognormal distributions are best suited to characterize a variety of aerosol components, the different aerosol types representing different environments, and their spatial and temporal variability. Aerosols get removed from the atmosphere by dry and wet deposition processes. The residence time of aerosols due to wet removal is found to vary from about a week in the lower troposphere to up to 3 weeks in the middle to upper troposphere.
