Retrospective trend analysis of the content of U.K. air particulate material 1957–1974

Abstract Particulate air samples have been collected on a daily basis in a high volume air sampler at Chilton (Oxfordshire U.K.) a semi-rural site in southern England from 1957 to 1974. Although the samples collected on esparto grass filters were intended to measure debris from nuclear weapons, they have proved susceptible to analysis for a variety of inorganic elements and ions. The concentration of twenty-seven elements and ions have been determined by instrumental neutron activation analysis and other methods. Measurements were performed on three-monthly groups of samples over seventeen years. Comparison with another series of current measurements over the latter part of the period indicate that the results are probably valid and thus, may represent the longest period for which continuous data of this nature are available. The detailed results are presented here. There are marked fluctuations in the levels displayed which can be categorised in three ways. There are seasonal changes. Winter levels, due either to increased emission rates or to meteorological phenomena, are greater than summer. The largest seasonal differences occur with chalcophilic (volatile) elements. Medium term fluctuations, in which excursions continue over extended periods, occur in similar ways with most constituents. A difference between the behaviour of anthropogenic and marine components indicate a meteorological mechanism for these changes. The most interesting changes are those showing long term trends. Many elements exhibit initial high levels with a rapid decline to 1961 and thereafter fall more slowly. The similarity of this behaviour with that of local “black smoke” indicates a component in the inorganic aerosol at Chilton from coal burning or industrial sources. The behavior of some lithophilic elements suggests an additional natural source. The behaviour of lead is consistent with a rise in emissions from petrol although there appears to be a residual component from other anthropogenic sources. A rise in bromine levels too, might be similarly explained. Vanadium appears to arise from the combustion of fuel oil now in increasing use. Concentrations of ammonium sulphate rise during the summers of the survey. It is likely that a photochemical mechanism for the production of sulphur dioxide oxidants from automobile exhaust is responsible. Similar photochemical processes and other reactions may cause the rises of ammonium nitrate although these display less seasonal bias. This survey at a single site demonstrates the value of data gathered over a long period, and emphasises the need to conduct controlled measurements for similar times at a variety of differing environmental and geographical locations.