Part 2. Time-series study on air pollution and mortality in Delhi

Air pollution concentrations in most of the megacities in India exceed the air quality guidelines recommended by the World Health Organization and may adversely affect human health in these cities. Particulate matter (PM) is the pollutant of concern in many Indian cities, particularly in the capital city of Delhi, In recent years, several actions have been taken to address the growing air pollution problem in Delhi and other Indian cities; however, few studies have been designed to assess the health effects of air pollution in Indian cities. To bridge the gap in scientific knowledge and add evidence to the ongoing studies in other Asian cities, a retrospective time-series study on air pollution and mortality in Delhi was initiated under the HEI Public Health and Air Pollution in Asia (PAPA) program.

The study used retrospective time-series data of air quality and of naturally-occurring deaths recorded in Delhi to identify changes in the daily all-natural-cause mortality rate that could be attributed to changes in air quality. The 3-year study period included the years 2002 through 2004. The methodology involved: (1) collecting data on ambient air quality for major pollutants from all monitoring stations in Delhi; (2) collecting meteorologic data (temperature, humidity, and visibility); (3) collecting daily mortality records from the Registrar of Births and Deaths; (4) statistically analyzing the data using the common protocol for Indian PAPA studies, which included city-specific modifications.

The study findings showed that increased concentrations of PM with an aerodynamic diameter < or = 10 microg/m3 (PM10) and of nitrogen dioxide (NO2) were associated with increased all-natural-cause mortality. It was found that every 10-microg/m3 change in PM10 was associated with only a 0.15% increase in total all-natural-cause mortality. When NO2 alone was considered in the model, daily all-natural-cause mortality increased 0.84% for every 10-microg/m3 increase in NO2 concentration. No significant effect was observed for changes in sulfur dioxide (SO2) concentrations. The study provides insight into the link between air pollution and mortality in local populations and contributes information to the existing body of knowledge.