A spatially disaggregated time-series analysis of the short-term effects of particulate matter exposure on mortality in Chennai, India

The global burden of disease due to air pollution is concentrated in the rapidly developing counties of Asia, but a recent meta-analysis found that relatively few studies on short-term exposure to air pollution and mortality have been performed in these countries, including India. Local evidence on the effects of short-term exposures to air pollutants on mortality and cardio-respiratory morbidity in Asia would reduce the uncertainties in current impact estimations and facilitate effective public policy responses to a deteriorating air pollution situation in South Asia. Here, we report the results from one of the first of such studies in metropolitan Chennai, India, conducted as part of a co-ordinated multi-city time-series initiative in India aimed at estimating the effect of short-term exposure to particulate matter ≤10 μm in aerodynamic diameter (PM₁₀) on all-cause mortality. The studies in Indian cities (Chennai, Delhi and Ludhiana) were part of a larger multi-city effort in Asia, co-ordinated by The Health Effects Institute (Boston, MA, USA) under their program for Public health and Air Pollution in Asia (PAPA). An important study output included the development of methodological refinements to overcome the limitations of routinely collected data in terms of missing measurements, small footprints of air pollution monitors and incomplete address information on death records. We used data on ambient air quality and all-cause mortality collected over the period 2002–2004. Exposures and health outcomes were disaggregated at the level of individual city zones and subsequently used in quasi-Poisson generalized additive models with smooth functions of time, temperature and relative humidity. Our model estimated a 0.44% (95% confidence interval?0.17–0.71) increase in mortality per 10 μg/m³ increase in daily average concentrations of PM₁₀, which is comparable to estimates from other PAPA cities and previous studies in North America and Europe. The results from PAPA studies in India, while preliminary, serve to strengthen the local evidence base for air pollution-related health effects that is imminently needed for better air quality management, while adding valuable information from India to the global repository of evidence.