Emission time and amount of crop residue burning play critical role on PM2.5 variability during October-November in northwestern India during 2022-2024

Abstract

High incidences of crop residue burning (CRB) in Punjab and Haryana during October-November is one of the major causes of elevated PM2.5 in Delhi National Capital Region (NCR). An estimation of precise contribution of CRB emissions to PM2.5 levels in Delhi-NCR is hindered by uncertainties in meteorology, atmospheric chemistry and emissions, and lack of quality observations. We use continuous in-situ observations of PM2.5 from a wide area network of 30 stations during 16 October to 30 November (peak CRB season) of 2022, 2023 and 2024 under Aakash project. The WRF-Chem model is used for simulation of chemical compositions of the atmosphere over the northwest India region. We have incorporated five distinct CRB emission scenarios in addition to commonly used industrial and biological emissions for the simulations. Scenarios with and without CRB emissions from different regions were compared to assess their impacts on PM2.5. The average CRB emission impact on PM2.5 concentrations in Delhi-NCR during CRB season are estimated at 18%, 16% and 9% in 2022, 2023 and 2024, respectively. The low impact of CRB on PM2.5 in 2024 could arise from a shift in CRB time to evening, which was not captured by existing emission inventories due to absence of satellite overpass in late evening. A shift to late evening CRB leads to very strong nighttime build-up of PM2.5 due to emissions when the boundary layer is shallow. Inclusion of appropriate diurnal and synoptic variability in CRB emissions is important for simulating observed PM2.5 levels and evaluation human health exposures.