Abstract

Delhi, the capital city of India with more than 10 million population, is suffering one of the worst particulate matter (or PM2 .5) pollution over the world. However, the long-term studies of it and mitigation devising is far from enough for advising Indian government. In this talk, I will briefly summarize the local characters and the unique of PM2 .5 pollution in Delhi, based on continuous ground observations over past 4 years. We find a distinct seasonal variation of PM2 .5 mass concentrations and a shift of morning rush hour from winter to summer, but a negligible weekend effect. The Diwali fest worsens short-term exposure to PM2 .5 by a factor of approximately 1.8, and leads to a mortality of approximately 22 person/day in Delhi. Our results also show that the atmospheric particles in Delhi are much more hygroscopic than the particles in Beijing or Asian average. It means, in addition to the great health burden, more significant cloud activation and hence greater influences on climate and hydrologic cycle are expected from particles in Delhi. It also implies a different chemical constituent (possibly less organics than Beijing and Asian average) of Delhi PM2 .5. With help of a regional chemical transport model (WRF-Chem) and an advanced statistical method (Gaussian Process emulation), we discuss the possibility of a series of mitigation plans. We foresee an increase of ozone risk in a current wide-agreed plan, which is mainly focusing on reducing PM2 .5 only. At the end of the talk, I will show you an optimized mitigation plan, concluded from thousands of sensitivity simulations/emulations. This plan can effectively reduce the PM2 .5 in Delhi meanwhile minimize ozone risk, although much greater politic efforts are required for regional controls over the National Capital Region of India.