Separating the Effects of Temperature and Season on Daily Mortality from those of Air Pollution in London: 1965–1972

Abstract

Most analyses of the large database of daily mortality and indices of pollution in London, England, have dealt with the confounding influence of ambient temperature and/or season by using empirical adjustment models in the determination of the regression coefficients for the pollutants. The conclusions about the influence of the measured pollutants, that is, aerosol strong acid (H+), sulfur dioxide (SO,), and black smoke (BS), on mortality have varied due, at least in part, to the selection of the form of the temperature/season adjustment model. We have taken an alternate approach to separate the influences of temperature, season, and ambient pollutant levels on daily mortality in Greater London between 1965 and 1972. In each season, the majority of days fell within one or two temperature ranges, within which the daily death rates also fell within narrow ranges. Within these restricted temperature and mortality ranges, preliminary analyses indicated that there were relatively strong associations between daily mortality and the daily logs of the concentrations of H⁺ and SO₂ that were not confounded by temperature or seasonal variations. By contrast, the associations between the daily log of 6.5 and daily mortality in these restricted ranges were weaker, especially in the winter and summer seasons. While a more comprehensive analysis of these London data and of other pollutant and mortality data sets is needed, these initial results suggest that this new approach can serve as a valuable complement to model-based approaches for studying associations between pollutant exposures and daily mortality.