Evidence of the rôle of indirect photochemical processes in the formation of atmospheric sulphate particulate

The mass concentration of atmospheric sulphate particles was determined during daylight for relatively short time intervals. Characteristics of atmospheric aerosols and trace gases and some meteorological parameters were measured simultaneously. It was found that in summertime the sulphate concentration, and the logarithm of the mole ratio of sulphate to sulphur dioxide, correlated well with the intensity of solar radiation in wavelengths 0·29-0·50 μm and with the temperature. It is expected, on the basis of these results, that sulphate particle formation is activated by some primary photochemical reaction followed by secondary thermal processes.