The duration of high SO2 concentrations in an urban atmosphere

SO2 concentrations have been continuously measured in the urban area of Milan at three stations and for three winter semesters from 1972 to 1974. The nine time series have been processed statistically with particular regard to the duration of the events for which the concentration exceeded some levels of interest. It has been found that all the statistics of interest are strongly dependent upon the six-month-average concentration, this value being easy to determine. Simple and accurate descriptive models have been formulated and verified.