Meta-analysis of time series studies and panel studies of particulate matter (PM) and ozone (O3). Report of a WHO task group

Quantitative health impact assessment has become increasingly important in the development of air quality policy. For such analysis it is important to have accurate information on the concentration-response relationships for the effects investigated, for example on the relationship between changes in daily air pollution and its impact on health. Therefore, a quantitative meta-analysis of peer reviewed studies was conducted to obtain summary estimates for certain health effects linked to the exposure to particulate matter (PM) and ozone. This work was done as part of the WHO project “Systematic review of health aspects of air pollution in Europe”, which is funded by the European Commission and is intended to provide input to the Clean Air For Europe (CAFE) programme. The data for these analyses came from a database of time-series studies (ecological and individual) developed at St. George’s Hospital Medical School at the University of London. The meta-analysis was also performed at St. George’s Hospital according to a protocol that was agreed upon by a WHO Task Group in advance of the work. This analysis confirmed statistically significant relationships between levels of PM and ozone in ambient air with mortality, using data from several European cities. Updated risk coefficients in relation to ambient exposure to PM and ozone were obtained for all-cause (relative risk for a 10 μg/m increase in PM10: 1.006 (1.004, 1.008) and ozone: 1.003 (1.001, 1.004), respectively) and cause-specific mortality and hospital admissions for respiratory and cardiovascular causes. In addition, possible publication bias was investigated and revised summary estimates were calculated. Also panel studies were analyzed to derive summary estimates for coughs and medication use in individuals with underlying respiratory disease.