Analysis of long-term measurements of airborne concentrations of sulphur dioxide and SO42- in the rural United Kingdom

During the last two decades, the importance of sulphur dioxide as a polluta nt has moved away from its association with suspended particulate matter, t o it being a precursor of SO42- aerosol (acidic e.g. sulphuric acid, or neu tralised e.g. ammonium sulphate). Co-located concentration data of sulphur dioxide and SO42-, at nine monitoring sites situated in predominantly rural areas in the United Kingdom, collected over the time period 1979-1995, hav e been analysed. The time series for both species are discussed for the sit es. Further analysis has shown that there is a degree of correlation betwee n sulphur dioxide and SO42- for most of the sites considered. This correlat ion is of approximately the same level for most of the sites taken independ ently and together, and in most cases the slopes and intercepts associated with the simple empirical model equations arising from the correlation anal ysis, are of the same order of magnitude. The implementation of these site- dependent model equations within dispersion models for the prediction of th e concentration of airborne sulphate aerosol from knowledge of sulphur diox ide concentration is discussed. Furthermore, the correlation analysis revea led the influence of transported sulphate aerosol on the local concentratio n, especially during high concentration episodes.