Short term effects of criteria air pollutants on daily mortality in Delhi, India

Various epidemiological studies conducted in different parts of the world have conclusively established that the adverse health effects are associated with common urban air pollutants. Although several recent studies revealed the poor air quality status in Delhi, but limited evidence of the impact of criterion air pollutants on human health remains a big limitation for relevant policy changes. So we conducted a time series to estimate the short term effects of ambient air pollution on all-natural-cause mortality in Delhi for the period 2008 to 2010. The study examined the impact of criteria air pollutants [particulate matter less than 10 μm in diameter (PM10), sulphur di-oxide (SO2), Nitrogen di-oxide (NO2), Carbon monoxide (CO) and Ozone (O3)] on daily all-cause-mortality rate. A semi-parametric regression model was developed to estimate the short term effects of air pollutants on daily all-natural-cause-mortality adjusting nonlinear confounding of time, temperature and relative humidity. A significant association of all-natural-cause mortality in association with short-term exposure to particulate as well as the gaseous pollutants were observed. The study estimated 0.14% (95% CI 0.02%-0.26%) increase in all-cause-mortality for every 10 μg/m3 increase in PM10 concentration. Among the gaseous pollutants, NO2 has been found to show most significant positive association of 1.00% (95% CI 0.07%-1.93%) increase in all-cause-mortality with every 10 μg/m3 increase in daily NO2 concentration. The effect of O3 and CO has been observed to be significant after controlling the effects of NO2. Analysis by different age groups reveals that particulate matter has maximum effect estimate in the age group ≥65 years (RR 1.002, 95% CI 1.000 to 1.004) whereas gaseous pollutants have been found to exhibit maximum effect estimate (RR 1.016, 95% CI 1.002 to 1.030) in the age group 5-44 years. The results of the present effect estimates appeared consistent with previous findings and can enhance the strength of the previous evidences to understand health burden associated with local air quality.