Air Pollution Over India: Causal Factors for the High Pollution with Implications for Mitigation

The fundamental motivation of this modeling study, which uses regional chemical transport models (Weather Research and Forecasting-Community Multiscale Air Quality Modelling System), is to distill the chemical, physical, and meteorological basis for the ultrahigh concentrations of fine particulate matter particles (PM2.5) over India. The study performed detailed source apportionment sensitivity studies with an updated sectoral emission inventory at 36 x 36 km resolution and the most recent meteorological data from the European Center for Medium-range Weather Forecasting. The Indo-Gangetic Plain (IGP) emerges as the most polluted region. PM2.5 concentrations over IGP and IGP cities like Delhi have year-round values of at least 80 mu g.m(-3) compared with World Health Organization guidelines of 5-15 mu g.m(-3). Peak pollution levels of 150-230 mu g.m(-3) in IGP occur from October through February, largely because of up to a fivefold drop in the ventilation coefficient and a lack of precipitation in winter in addition to increased emissions due to biomass burning. Emissions of primary particles (black carbon, dust, metals, and primary organics) contribute 38% of PM2.5 concentrations in India, while the remaining 62% is of secondary origin through gas-to-particle conversion. Cooking and heating with solid biomass contribute one-third of the PM2.5. Fossil fuel sources contribute 30%, largely as secondary aerosols. Emission inventories for black carbon may be underestimating emissions by a factor of 3. In major IGP cities like Delhi, the regional transport of particulates and gaseous pollutants emitted from various sources upwind play a major role in the PM2.5. Providing access to clean energy to the biomass dependent 500 million people and switching from fossil fuels to renewable energy sources would eliminate more than 60% of the PM2.5 over India, including the heavily polluted IGP.