Chowdhury, S; Dey, S; Di Girolamo, L; Smith, KR; Pillarisetti, A; Lyapustin, A (2019). Tracking ambient PM2.5 build-up in Delhi national capital region during the dry season over 15 years using a high-resolution (1 km) satellite aerosol dataset. ATMOSPHERIC ENVIRONMENT, 204, 142-150.
The Delhi National Capital Region (NCR) is among the most polluted areas in the world. We tracked ambient PM2.5 (fine particulate matter) build-up in Delhi NCR during the dry season (October-June) by analysing 15 years (2001-02 to 2015-16) of high-resolution (1 km) satellite data that has been bias corrected using coincident in-situ data. Ambient PM2.5 concentrations are 1.25 times lower in the upwind regions compared to the downwind areas of Delhi NCR, with the difference being attributed to outflow from the Delhi National Capital Territory (NCT). We identify two major peak pollution episodes - the first occurs from the end of October to early November, while the second occurs toward the end of December through early January. Mean ambient PM2.5 concentrations remain > 300 mu g/m(3) (five times the Indian 24-h national standard) for several weeks around the two peak pollution episodes. The first peak is attributed to pollution transport from upwind areas affected by open biomass burning, coupled with stable atmospheric conditions, while the second is attributed to enhanced local emissions and perhaps secondary aerosol formation under favorable meteorological conditions. The implementation of the "Sub-soil Water Preservation Act" in 2009 in Punjab (a state upwind of Delhi NCI) reduced the time between paddy and wheat cultivation seasons; as a result, open biomass burning increased, resulting in a 9% increase in weekly PM2.5 concentration over Delhi NCT since 2009 during the first pollution episode. To the best of our knowledge, this is the first time MODIS MAIAC 1 km satellite data are used to generate pollution statistics over India. Our results demonstrate the potential of high resolution satellite data in tracking pollution build-up at an urban scale and may help in air quality management.