Seasonal and geographic variations in imaginary refractive index of atmospheric particulate matter.

Samples of atmospheric particulate matter were collected on cellulose membrane filters at selected locations in Europe during 1976 and 1977 as part of an international cooperative atmospheric characterization program. These samples are analyzed for imaginary refractive index in the 0.3-1.7-microm spectral region. These data are used to determine the range of variability of the imaginary refractive index and are examined for seasonal variations. These data are discussed in the light of results of analysis of samples collected from other parts of the world and samples that were analyzed as a function of particle size.