Emission estimates and trends (1990–2000) for megacity Delhi and implications

A comprehensive emission inventory for megacity Delhi, India, for the period 1990–2000 has been developed in support of air quality, atmospheric chemistry and climate studies. It appears that SO2 and total suspended particles (TSP) are largely emitted by thermal power plants (∼68% and ∼80%, respectively), while the transport sector contributes most to NOx, CO and non-methane volatile organic compound (NMVOC) emissions (>80%). Further, while CO2 has been largely emitted by power plants in the past (about 60% in 1990, and 48% in 2000), the contribution by the transport sector is increasing (27% in 1990 and 39% in 2000). NH3 and N2O are largely emitted from agriculture (∼70% and ∼50%, respectively), and solid waste disposal is the main source of CH4 (∼80%). In the past TSP abatement to improve air quality has largely focused on traffic emissions; however, our results suggest that it would be most efficient to also reduce TSP emissions by power plants. We also assessed the potential large-scale transport of the Delhi emissions based on 10-day forward trajectory calculations. The relatively strong growth of NOx emissions indicates that photochemical O3 formation in the regional environment may be increasing substantially, in particular in the dry season. During the summer, on the other hand, convective mixing of air pollutants may reduce regional but increase large-scale, i.e. hemispheric effects.