Sun Photometry

Abstract

Multi-wavelength sun photometry has been a subject of interest in meteorology for two and a half centuries. The technique provides a quantitative index that relates to total suspended aerosol in the atmospheric air column above the observer; this aerosol changes continually in the atmosphere in response to many complicated physical processes. When used in conjunction with other aerosol and meteorological measurements, sun photometry has the capability of delineating characteristic features of different air masses and the aerosol sources that affect them. This paper traces some of the early history of sun photometry and discusses a simple but modern filter wheel sun photometer and several sources of systematic error that have to be reckoned with. We provide examples of aerosol optical extinction spectra acquired at remote and pollution-prone stations with a simple and portable sun photometer.