Assessing the variability in emissions from crop residue burning in north India using remote sensing data

Open biomass burning is the major cause for air pollution in north India, particularly in the months around the harvest of the major crops viz. rice and wheat. Crop residue burning, in the two agricultural powerhouse states of Punjab and Haryana, is major contributor for emissions from open biomass burning in the region. A district-wise emission inventory is needed to quantify the variations of crop residue burning emissions within various districts of Punjab and Haryana. In this study, bottom-up approach is used to determine the spatial variation of these emissions. In this approach, burned area is detected by using two MODIS satellite data products i.e., MODIS burned area product (MCD64A1) having resolution of 500m and MODIS active fire product (MOD14A1) having spatial resolution of 1km which can detect fires up to 1/20 of a pixel. Combining these two products the small fires data can also be detected and the accuracy in detection of burned area is improved. After detecting the burned area, the emissions of major pollutants were estimated in grids of (3×3) km² during 2008-2017 in order to analyze their spatial and temporal variability. Also, the emissions for the study region are estimated using top-down approach where the crop residue burned is determined using IPCC guidelines and the comparison is done using both the approaches.

In Punjab, the average emissions of PM_2.5, PM₁₀, CO₂ & CO are 153.3 Gg, 173.6 Gg, 21185.7 Gg, 1791.6 Gg, respectively during 2008-17 using top-down approach. During 2008-2017, the average emissions of PM_2.5, PM₁₀, CO₂ & CO are 117.2 Gg, 120.7 Gg, 18859.9 Gg, 1133.7 Gg, respectively using bottom-up approach. The major contribution of emissions in Punjab is from Sangrur district followed by Patiala and Ludhiana district.  In Haryana, the average emissions of PM_2.5, PM₁₀, CO₂ & CO are 68.9 Gg, 78.0 Gg, 9518.4 Gg, 804.9 Gg, respectively during 2008-17 using top-down approach. During 2008-2017, the average emissions of PM_2.5, PM₁₀, CO₂ & CO are 28.2 Gg, 26.4 Gg, 5214.0 Gg, 214.0 Gg, respectively using bottom-up approach. The major contribution of emissions in Haryana is from Fatehabad district followed by Karnal and Kaithal district. For Haryana, the peak emissions during 2008-17 are in the month of May and November and for Punjab the peak emissions are in the month of October and November. From the results, it is observed that the top-down approach overestimates the emissions when compared to the bottom-up approach. For example, the CO₂ emissions calculated using top-down approach is 1.1 and 1.8 times higher than the bottom-up approach for Punjab and Haryana, respectively. This is because a fixed value of fraction of biomass burnt is taken to estimate the amount of crop residue burned from the crop production values instead of accounting for area which are actually burned.

The development of the longer term emission inventory from crop residue burning may provide useful information for policy making on air pollution control in the region.