Tracking NO2 emission from thermal power plants in North India using TROPOMI data

Abstract

Exposure to air pollution is the largest environmental health risk in India, where the coal-fed thermal power plants (TPPs) are identified as the single largest air pollution source. The key to an efficient air quality management plan is strict compliance of the TPPs with emission norms. Yet, in-situ measurements are lacking, and the bottom-up emission inventory is not periodically updated in India. Here we adopt a top-down approach to estimate NO2 emission from nine TPPs within 300 km of the megacity Delhi using TROPOspheric Monitoring Instrument (TROPOMI) data. We first estimate the NO2 lifetime for each TPP using an e-folding decay length along the wind direction and combine it with the NO2 columnar molecular density to estimate the NO2 emission. Our estimates show a correlation coefficient of 0.88, and a root mean square error of 4.15 kt/year with the ECLIPSE V5 bottom-up inventory. NO2 emission in these TPPs varied in the range of 8.0–30.6 kt/year with considerable seasonal variability. Using this data, we report a decrease in NO2 emission in the range 41%–290% during the COVID-19 lockdown period relative to the same period in the previous year. As India launched the National Clean Air Program to control air pollution, our method would be highly useful in tracking the emission compliance of the TPPs across the country.