Year-long simulation of gaseous and particulate air pollutants in India

Severe pollution events occur frequently in India but few studies have investigated the characteristics, sources, and control strategies for the whole country. A year-long simulation was carried out in India to provide detailed information of spatial and temporal distribution of gas species and particulate matter (PM). The concentrations of O_3, NO_2, SO_2, CO, as well as PM_(2.5) and its components in 2015 were predicted using Weather Research Forecasting (WRF) and the Community Multiscale Air Quality (CMAQ) models. Model performance was validated against available observations from ground based national ambient air quality monitoring stations in major cities. Model performance of O_3 does not always meet the criteria suggested by the US Environmental Protection Agency (EPA) but that of PM_(2.5) meets suggested criteria by previous studies. The performance of model was better on days with high O_3 and PM_(2.5) levels. Concentrations of PM_(2.5), NO_2, CO and SO_2 were highest in the Indo-Gangetic region, including northern and eastern India. PM_(2.5) concentrations were higher during winter and lower during monsoon season. Winter nitrate concentrations were 160–230% higher than yearly average. In contrast, the fraction of sulfate in total PM_(2.5) was maximum in monsoon and least in winter, due to decrease in temperature and solar radiation intensity in winter. Except in southern India, where sulfate was the major component of PM_(2.5), primary organic aerosol (POA) fraction in PM_(2.5) was highest in all regions of the country. Fractions of secondary components were higher on bad days than on good days in these cities, indicating the importance of control of precursors for secondary pollutants in India.