Source attribution of nitrogen dioxide over the Indian subcontinent using WRF-chem

Abstract

Present study investigated the contribution of various source regions/types of NO2 over the Indian subcontinent using WRF-Chem model during 2015. Model simulated NOx is able to reproduce the major observed features over Pune, Udaipur and Dehradun. The relative NO2 contribution from five regional sectors namely Northern, Eastern, Southern, Western India and North-East India & Myanmar was analysed by enabling anthropogenic emissions of NOx only over the chosen regional sector. NO2 distribution at 900 hPa showed that the eastern, northern, western, southern and North-east India & Myanmar regions receive contribution of 10.81 ± 6.96 ppbv, 6.02 ± 6.57 ppbv, 6.52 ± 3.99 ppbv, 3.29 ± 3.62 ppbv and 1.65 ± 1.18 ppbv respectively from local regional emissions. To quantify the contribution from Energy, transport, industry and agriculture sectors, model simulations were made enabling each type of anthropogenic emission separately. Over eastern, western and north eastern regions, maximum NO2 is contributed from the energy sector with 5.58 ± 4.44 ppbv, 3.70 ± 2.82 ppbv and 1.64 ± 1.33 ppbv respectively. However, over Northern and Southern regional sectors, contribution of transport exceeded from energy contribution by 0.6 ppbv and 0.25 ppbv respectively. Model simulations were made with reduced anthropogenic emissions to understand its impact on other criteria pollutant ozone. Reduction of NOx anthropogenic emissions by 30% over the simulation domain resulted in a decrease of ozone at 900 hPa by up to 40 ppbv and free tropospheric ozone by 20–30 ppbv. A nonlinear behaviour of ozone with respect to NOx was evident over certain parts of northern India during winter and autumn. These results highlight the importance of different source regions/types of NOx anthropogenic emissions over India.