Interacting effects of particulate pollution and cold temperature on cardiorespiratory mortality in Scotland

Abstract

Objectives: To determine whether the effect of black smoke on cardiorespiratory mortality is modified by cold temperatures. Methods: Poisson regression models were used to investigate the relationship between lagged black smoke concentration and daily mortality, and whether the effect of black smoke on mortality was modified by cold temperature, for the three largest Scottish cities (Glasgow, Edinburgh and Aberdeen) over the period January 1981 to December 2001. Main results: For all cause, respiratory and non-cardiorespiratory mortality, there was evidence of a significant association between mortality and lagged black smoke concentration (up to approximately 2 to 4 weeks). Generally the maximum black smoke effect occurred at lag 0, although these estimates were not statistically significant. A significant association between cardiovascular mortality and black smoke was not observed. A 10 µgm-3 increase in the daily mean black smoke concentration on any given day was associated with a 1.68 percent (95% CI: 0.72, 2.65) increase in all cause mortality and a 0.43 percent (95% CI: -0.97, 1.86), 5.36 percent (95% CI: 2.93, 7.84) and 2.13 percent (95% CI: 0.82, 3.47) increase in cardiovascular, respiratory and non-cardiorespiratory mortality, respectively, over the ensuing 30-day period. There was no evidence that the effect of black smoke on mortality varied significantly between seasons (cool and warm periods). There was a suggestion of a modest interaction between black smoke and temperature in their effect on respiratory mortality, with the results indicating that this interaction is confined to the lowest temperature range. For all cause, cardiovascular and non-cardiorespiratory mortality the inclusion of interaction terms did not improve the models, although for all cause, and non-cardiorespiratory mortality there was a suggestion for interaction between temperature and recent black smoke exposure. Conclusions: The results of this study have suggested modest evidence of a greater effect of black smoke on mortality at low temperatures. Since extremes of cold and particulate pollution may coexist, for example during temperature inversion episodes, the results of this study may have important public health implications.