Air pollution and daily mortality in London: 1987-92

Abstract

Objective : To investigate whether outdoor air pollution levels in London influence daily mortality. Design : Poisson regression analysis of daily counts of deaths, with adjustment for effects of secular trend, seasonal and other cyclical factors, day of the week, holidays, influenza epidemic, temperature, humidity, and autocorrelation, from April 1987 to March 1992. Pollution variables were particles (black smoke), sulphur dioxide, ozone, and nitrogen dioxide, lagged 0-3 days. Setting : Greater London. Outcome measures : Relative risk of death from all causes (excluding accidents), respiratory disease, and cardiovascular disease. Results : Ozone levels (same day) were associated with a significant increase in all cause, cardiovascular, and respiratory mortality; the effects were greater in the warm season (April to September) and were independent of the effects of other pollutants. In the warm season an increase of the eight hour ozone concentration from the 10th to the 90th centile of the seasonal range (7-36 ppb) was associated with an increase of 3.5% (95% confidence interval 1.7 to 5.3), 3.6% (1.04 to 6.1), and 5.4% (0.4 to 10.7) in all cause, cardiovascular, and respiratory mortality respectively. Black smoke concentrations on the previous day were significantly associated with all cause mortality, and this effect was also greater in the warm season and was independent of the effects of other pollutants. For black smoke an increase from the 10th to 90th centile in the warm season (7-19 µg/m 3 ) was associated with an increase of 2.5% (0.9 to 4.1) in all cause mortality. Significant but smaller and less consistent effects were also observed for nitrogen dioxide and sulphur dioxide. Conclusion : Daily variations in air pollution within the range currently occurring in London may have an adverse effect on daily mortality. Key messages: Evidence from other countries suggests that similar levels of pollution may be associated with short term health effects This study suggests that air pollution due to particles and ozone may be associated with increased daily mortality in London The evidence is less convincing for nitrogen dioxide and sulphur dioxide It would be prudent to assume that these associations are causal and to reduce air pollution levels with the help of appropriate abate- ment policies