Characterization and health risks of criteria air pollutants in Delhi, 2017.

Severe air pollution events were observed frequently in north India in recent years especially at its capital, Delhi. Criteria air pollutants data at 10 sites for 2017 in Delhi were analyzed. The results show annual fine particulate matter (PM) concentrations exceeded the National Ambient Air Quality Standards (NAAQS) of 60 μg/m at all sites from 105.51 (site 10) to 143.23 μg/m (site 7). Sub-urban sites (site 8, 9 and 10) had lower PM concentrations than urban sites. Coarse PM (PM) and ozone (O) were also important with annual averages of 399.56 μg/m and 75.69 ppb, respectively. Peak PM occurred at the Diwali in early November and Christmas. Only PM showed a significant weekly difference with a weekdays/weekends ratio of ∼1.5. PM/PM ratio in episode days with PM of >60 μg/m was higher than non-episode days. Pearson correlation coefficients show O was negatively related with CO, SO, and NO, while PM was positively related to these pollutants. Analysis of two extreme events from Nov. 6th to Nov. 14th and Dec. 18th to Dec. 26th shows that meteorological conditions with low wind speed and warm temperature kept PM concentrations at a high level during these events. Backward trajectory and cluster analysis show the wind coming from northwest of Delhi, where massive anthropogenic emissions were generated, led to high concentrations of air pollutants to Delhi. Health risk analysis reveals that PM and PM were the two major pollutants threatening public health among the six criteria pollutants.