Assessment of local and regional air quality for Delhi, India within the South Asia-Cordex Domain

Both long range transport of air pollution and local sources such as road vehicles contribute significantly to the high levels of urban air pollution. The purpose of this study is to quantify and examine the spatial distribution of these two main sources of air pollution affecting Delhi. We have extended this study to examine how climate change may affect future air quality in the region. As part of the PROMOTE project, funded by NERC/MOES, WRF and CMAQ model have been utilised to analyse the effects of road transport emissions on air quality in Delhi. CMAQ model was configured with WRF meteorology for four nested domains over India with resolutions of 45km, 15 km, 5 km, and 1.6 km for 2018. NCEP/FNL data was used to drive WRF while CMAQ model was driven using EDGAR v5.0 emission inventory (for 2015) and Cam-Chem initial and boundary condition. The baseline runs kept all domains unchanged in terms of emissions, while in a scenario simulation, the road transport sector was eliminated from the third domain (5km) to assess the influence of road transport emissions in the Delhi urban area. The model's performance for PM10, PM2.5, NOx, NO2 and O3 was evaluated using available observations.In the next part of the study, the OSCAR model was used to forecast air quality in Delhi and assess the impact of road transport emissions. The study investigated the monthly and seasonal contributions of local and regional transport sources to Delhi's air quality and evaluated the interconnections between these sources of pollution. The study's third phase assessed climate change's impact on Delhi's future air quality using the SSP245 (middle-of-the-road) scenario as part of a NERC-funded COP26 project. WRF model was driven by bias-corrected Coupled Model Intercomparison Project Phase 6 (CMIP6) data through a dynamical downscaling method for 2015 (representative of 2011-2020) and 2050 (representative of 2046-2055) over the South Asia-Cordex domain at 27 km spatial resolution. The CMAQ model was used with averaged meteorology, future land use, initial and boundary conditions, and future emissions data for India, spanning ten years. The model was tested using both ten years' averaged meteorology and only 2015 meteorology.The use of ten-year averages around the desired year, while suppressing diurnal variations, provided insights into monthly changes in climate and air quality parameters. The CMAQ model predicted significant anomalies (2050-2015) in PM2.5, PM10, NOx, and O3 under the selected SSP245 scenario, with monthly means ranging from 8 to 41 μg/m3 over India. Considerable differences in PM2.5, PM10, NOx, and O3 anomalies were observed before and after Monsoon months (June to October) in urban regions such as Delhi.

Financial Support: We acknowledge funding from NERC/MOES (NE/P016391/1) for the PROMOTE project and NERC (2021COPA&R48Sokhi) for the COP26 project.