Evaluation of black carbon emission inventories over Indian subcontinent: role of open biomass burning and its representation in emission fluxes

Abstract

Black carbon (BC) aerosols play an important role in air pollution, environment, and climate. Emission inventories of BC are key inputs for atmospheric models that assess the impact of BC emissions on health and the environment. However, estimated BC emission fluxes are highly uncertain. In this study, we evaluated three emission inventories — the Community Emission Data System (CEDS), the Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants (ECLIPSE) and Global Fire Emission Database (GFED) — using the Lagrangian dispersion model FLEXPART, along with BC observations from two locations in India viz. Ahmedabad (urban) and Gadanki (rural). The modeled BC concentrations using ECLIPSE and CEDS were comparable to each other; however, the modeled BC concentrations were underestimated by a factor of 2 using these emission inventories. The annual mean biases between model and observation (observation-model) are approximately 3 μg/m3 and 1 μg/m3 at Ahmedabad (urban) and Gadanki (rural), respectively. Adding the contribution of biomass-burning sources from the GFED inventory (less than 0.01 μg/m3) did not significantly improve the bias. Open biomass burning (OBB) emissions, resulting from large-scale burning of biomass in agricultural fields, forests, and wastelands, is the largest contributor to BC concentrations globally and are highly uncertain. To investigate the underestimation of BC by the model and the role of OBB emissions in this discrepancy, a novel rank-based statistical framework is developed. This framework integrates satellite-detected fire hotspots, FLEXPART model, and ground-based observations to evaluate relative contribution of OBB emissions to BC concentrations. We find that OBB emissions are not a significant source of BC concentrations over Ahmedabad (23.03°N, 72.55°E). In contrast, BC emissions from OBB are underestimated at Gadanki (13.48°N, 79.18°E). The framework used to evaluate cause-effect relation between OBB and BC can help constrain better the sources of BC. This framework can be readily extended globally to evaluate other sectors where emission activity data can be observed using satellites.