Assessing changes to the probability distribution of sulphur dioxide in the UK using a lognormal model

This study investigates whether there has been any change in the concentration probability distribution of sulphur dioxide at 10 United Kingdom monitoring sites over time periods of up to 40 yr. It is a large and comprehensive study in terms of geographical and temporal extent. The lognormal probability plot, its associated correlation coefficient and a test for significance are used to fit and assess how well a 2-parameter lognormal distribution describes the data. Daily data are analysed at all sites on an annual basis and further seasonal and meteorological investigations are undertaken at two of the sites. The lognormal is found to be a good and robust fit for a variety of conditions. The level of lognormality has stayed relatively constant over a large range of ambient mean sulphur dioxide levels. To explain the lognormal distribution and specific departures, a physically based stochastic model is proposed which not only develops the idea of successive random dilutions (J. Air Waste Manage. Assoc. 40 (1990) 1378) but also includes the processes of deposition, chemical reaction and emission.