Long-term variations and source sectors of criteria pollutants in megacities across India

There are a large number of air pollutants present in the ambient air. Amongst them, 6 have been listed as criteria air pollutants by the US Environmental Protection Agency (EPA). They are, namely, NOx, CO, SO2, O3, PM and Lead. In terms of effects on human health, these criteria pollutants have both long term as well as short term effects. Amongst the many health effects, acute health effects, which are due to short term exposure includes: irritation of eyes, nose, throat, coughing, difficulty breathing, inflamed lung tissue etc. The objective of this study is to investigate the long term trends of the criteria air pollutants (NO, NO2, CO, SO2, O3, PM2.5 and PM10) in selected Indian megacities namely Bengaluru, Delhi, Chennai and Mumbai. We will study the long term seasonal, monthly and yearly trends. We also tried to identify potential source sectors in these megacities in order to understand relative contributions from local and regional sources. The study has been done over four metropolitan cities in India, i.e. Bengaluru, Chennai, Delhi and Mumbai. Based on the present work, it can be concluded that the emission environment is not same in all the cities and the pollutants show different behaviours in different cities. There is large variations in yearly and seasonal trends of these pollutants across cities. The seasonal variations of criteria pollutants are compatible with expectations from well-established formation and removal processes in the atmosphere. Concentration weighted trajectories analysis shows that relative contribution from local and transboundary sources of criteria pollutants vary considerably between cities, emphasizing the need to have city-specific emission standards and control policies.