Photometric study o f atmospheric pollution

A photometric method of comparing the loss of reflecting value through tarnishing of polished metal plates is described and shows the wide daiiy and seasonal effects of changes in the polluting media in the atmosphere for different metals simultaneously exposed in the same place. The different rates of tarnishing of the same metal plates exposed during the same week in rural, London and industrial areas are very marked. Extreme cases in Westminster for polished copper are losses of 38 and 50 per cent in five hours in December fogs, whereas on four successive days in February, 1936, the loss in five hours varied between 5 and 11 per cent. For a summer day in 1935 a 10 per cent loss in 24 hours seems normal. For short periods of say, one to two days in the winter and a week in the summer, copper is a good indicator. For longer periods “fine” silver is better. Aluminium responds slowly while the useful range of nickel appears t o be between those of copper and of silver. In two appendices, the loss of reflection value is correlated with independent measurements of sulphur in the atmosphere. Further lines of research are indicated.