Multi-satellite observations of NOx emissions increase in Indian thermal power sector from 1996 to 2010

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Description

Nitrogen dioxide (NO2) and nitric oxide (NO), together known as nitrogen oxides (NOx), have broader effects on human health, atmospheric composition, acid deposition, air/water quality, visibility, radiative forcing, etc. As the second largest NOx emitting country in Asia, India is of increasing concern. Thermal power plants are the most important point sources in India, and their NOx emissions (E) have been reported to increase at a remarkable rate since the mid-1990s due to the rapid economic development, the growing electricity demand, and the absence (or weak enforcement) of regulations. In this study, we present the NOx emissions from Indian public thermal power plants for the period 1996−2010 using a unit-based methodology and compare the emission estimates with the satellite observations of NO2 tropospheric vertical column densities (TVCDs) from four spaceborne instruments: GOME, SCIAMACHY, OMI, and GOME-2. Results show that NOx emissions from Indian power plants increased by at least 70% during 1996−2010. Coal-fired power plants, NOx emissions from which are not regulated in India, contribute ~96% to the total power sector emissions, followed by gas-fired (~4%) and oil-fired (<1%) plants. A number of isolated NO2 hot spots are observed over the power plant areas, and they match the locations of thermal power plants reasonably well. Good agreement between NO2 TVCDs and NOx emissions is found, especially for areas dominated by power plant emissions. Average NO2 TVCDs over power plant areas were continuously increasing during the study period, and power plants are estimated to contribute more than 90% to the increment. We find that the ratio of ΔE/E to ΔTVCD/TVCD changed from greater than one to less than one around 2005−2008, implying that a transition of the overall NOx chemistry occurred over the power plant areas, which may cause significant impact on the atmospheric environment. The results of this work provide us a better understanding of the large NOx releases from the Indian power sector for recent years, and further contribute to our ongoing attempts to assess the usefulness of satellite retrievals for quantifying large point source (LPS) emissions.