REGIONAL AIR QUALITY MODELING IN INDIA USING CHEMICAL TRANSPORT MODEL

Abstract

Over the last decades, the increases in anthropogenic emissions of particulates/aerosol and trace gases have resulted in a significant increase in air pollution levels across the India. The current state of air pollution in India, particularly PM2.5 pollution, has been found very critical. This pollution loading reaches much higher levels in the winter season due to adverse meteorological conditions, which limit pollutant dispersion and generate higher concentrations near the earth's surface. However, wintertime severe pollution loadings in India are still relatively understudied. This thesis focuses on improving our understanding of wintertime pollution loadings over India using an online WRF-Chem model. Air quality simulations have been carried out for the 2015-16 winter period over the Indian subcontinent at a high grid resolution of 12 km × 12 km, and gas and aerosol chemistry are simulated using the CBM-Z and MOSAIC-4bin modules. Emissions from the EDGAR-HTAP v2.2 database are used, scaled to the simulation year based on changes in activity data for each Indian state, which increases national emissions of PM2.5, BC, OC, NOx, SO2 and NMVOCs by 2.6, 0.3, 0.5, 6, 13.5 and 3.6 Gg/day, respectively, in winter. The model performance was evaluated in relation to ground-based measurements in major cities. It was found that the PM2.5 predictions by the model fulfilled the excellent performance criterion (Mean Fractional Bias range -0.15 to 0.11) in most cities. The NO2 concentrations were reproduced well by the model with a Mean Fractional Bias range of -0.17 to 0.25, whereas underprediction of CO and over-prediction of O3 were detected with mixed model performance. Patterns of diurnal cycles of pollutants were found to be broadly similar for both measurements and model predictions. The spatial distributions of predicted mean PM2.5, NO2, and CO pollution loadings showed higher concentrations in northern part of India, particularly over the IGP region. PM2.5 concentrations in the IGP region were found to be greater than 100 μg/m3, significantly exceeding the Indian NAAQS. Sensitivity study was carried out to investigate the role of major sectors and different states of IGP in local and regional higher PM2.5 pollution. Over the IGP, the residential and transportation sectors emerged as the primary contributors to ambient PM2.5 pollution, while industrial and energy sectors contributions varied considerably with higher contributions at and around industrial (~ 20 %) and power plant clusters (~30-40 %). Source apportionment of PM2.5 pollution at major i cities in IGP revealed that transportation sector in cities of upper IGP states and residential sector in cities of middle and lower IGP states are the leading contributors. The analysis of source region contributions found that, in addition to larger contributions to local PM2.5 pollution loadings, there were also considerable regional contributions. The short-term health impacts due to PM2.5 exposure were estimated over India, which showed higher mean mortalities over IGP states {1409 (763-1965) persons/day} and megacities Delhi {61 (33-91) persons/day}, Kolkata {44 (23-64) persons/day} and Mumbai {40 (22-55) persons/day}. Source apportionment of mean short-term premature mortality in each IGP state indicated higher local source state contributions (~30-59%), as well as significant contributions from other IGP states (~14-53 %). The PM2.5 pollution loadings in 53 MPPC’s of India were also assessed. PM2.5 concentrations were found to be higher in most MPPC’s, above the Indian NAAQS and WHO standard, and significant regional contributions in PM2.5 pollution of all MPPC’s were detected. Along with higher contributions to local PM2.5 pollution of MPPC’s, pollution plumes of each source sector from these MPPC’s also showed potential to contribute in regional PM2.5 pollution. Source sector contributions to local PM2.5 pollution of MPPC’s revealed that in most MPPC’s, the residential sector is the primary contributor. However, MPPC’s located in the regions of industrial and power plant clusters showed industrial and energy sector as largest contributors. Similarly, for MPPC’s located in the upper IGP region, transportation sector showed higher fractions in local PM2.5 pollution. The investigation of correlation between meteorological parameters and PM2.5 pollution in MPPC’s discovered that wintertime pollution loadings in MPPC’s across India are influenced not just by city emissions, but also by spatial variations of wind speed and boundary layer height across India, which control the pollution dispersion.