Evaluation of emission strength efficacy in simulating black carbon burden with CHIMERE: estimating wintertime radiative effect over Indo-Gangetic Plain

Black carbon (BC) aerosols over the Indian subcontinent have been represented inadequately so-far in chemical transport models restricting the accurate assessment of BC-induced climate impacts. The divergence between simulated and measured BC concentration has specifically been reported to be large over the Indo-Gangetic Plain (IGP) during winter when a large BC burden is observed. In this study, we evaluate the BC transport simulations over the IGP in a high resolution (0.1º × 0.1º ) chemical transport model, CHIMERE. We examine the model efficiency to simulate the observed BC distribution executing five sets of simulation experiments: Constrained and bottomup (Smog, Pku, Edgar, Cmip) implementing respectively, the recently estimated India-based constrained BC emission and the latest bottom-up BC emissions (India-based: Smog-India, and global: Coupled Model Intercomparison Project phase 6 (CMIP6), Emission Database for Global Atmospheric Research-V4 (EDGAR-V4) and Peking University BC Inventory (PKU)). The mean BC emission flux over most of the IGP from the five emission datasets is considerably high (450–1000 kg km^-2 y^-1) with a relatively low divergence obtained for the eastern and upper-mideastern IGP. Evaluation of BC transport simulations shows that the spatial and temporal gradient in the simulated BC concentration from the Constrained was equivalent to that from the bottomup and also to that from observations. This indicates that the spatial and temporal patterns of BC concentration are consistently simulated by the model processes. However, the efficacy to simulate BC distribution is commendable for the estimates from Constrained for which the lowest normalised mean bias (NMB, < 20%) is obtained in comparison to that from the bottomup (37–52%). 75–100% of the observed all-day (daytime) mean BC concentration is simulated most of the times (>80% of the number of stations data) for Constrained, whereas, this being less frequent (<50%) for the Pku, Smog, Edgar and poor for Cmip. The BC-AOD (0.04–0.08) estimated from the Constrained is 20–50% higher than the Pku and Smog. Three main hotspot locations comprising of a large value of BC load are identified over the eastern, mideastern, and northern IGP. Assessment of the effect of BC burden on the wintertime radiative perturbation over the IGP shows that the presence of BC aerosols in the atmosphere enhances atmospheric heating by 2–3 times more compared to that considering atmosphere without BC. Also, a net warming at the top of the atmosphere (TOA) by 10–17 W m^-2 is noticed from the Constrained, with the largest value estimated in and around megacities (Kolkata and Delhi) that extends to the eastern coast. This value is higher by 10–20% than that from Cmip over the IGP and by 2–10% than that from Smog over Delhi and eastern part of the IGP.