The dispersion of sulphur dioxide in the town of Reading has been studied for a period of 15 months. Continuous measurements of the 6-hr average concentrations were made at forty sites in the area, and meoterological measurements were made for each 6-hr period. A detailed inventory was prepared of both domestic and industrial sources of sulphur dioxide.It is shown that, of various meteorological ... [Show full abstract] variables examined, the ambient air temperature has the predominant effect on the sulphur dioxide concentration in the air. The basis for the “degree-day method” is confirmed in that the average concentration over the town increases linearly with the difference of the air temperature below a datum value of 15° C. Isopleths of annual sulphur dioxide concentration have been drawn for eight wind directions; these show that the distribution of pollution is not greatly affected by wind direction although variations in the average air temperatures for different wind directions affect the general level. A pollution rose for the town as a whole shows that there is an excess of sulphur dioxide arriving from the east and this is attributed to pollution from London; some pollution also arrives from external sources in other directions.The annual average concentration of sulphur dioxide at individual sites is strongly correlated with the consumption of local installations emitting their effluents from chimneys less than 21 m high; an empirical equation is given for Reading relating annual concentrations with consumption within 1000 m of the measuring point.Pollution roses have been drawn for each measuring site and these give a qualitative indication of the pollution from Reading, but a detailed comparison of individual vectors with the distribution of sources has failed to show a satisfactory correlation. The pollution roses do not indicate the larger industrial installations and it is considered that the chief contribution to the pollution in Reading is from domestic and low industrial chimneys.