Radiative Feedback of Carbonaceous Aerosols over the Indian Subcontinent

Black carbon (BC) with a radiative forcing of 1.1 W/m² is the second largest contributor to global warming after CO₂. Carbonaceous aerosols are also a large component of fine particulate matter responsible for the haze observed in the Indo-Gangetic Basin. Key to curb climate change lies in mitigating the short lived climate pollutants (SLCP) such as BC to maximize climate and health co-benefits. Previous studies on BC impact on Indian climate are mostly limited to the monsoon season; that too with global climate models. Here we have used a regional climate model to simulate BC distribution over the Indian subcontinent at finer resolution (25 km) to examine the BC radiative feedback on the meteorology and hydrological cycle. The model is customized for this region by incorporating a regional emission inventory. In this study, we have performed 3-sets of long term simulations from 2006-2015 to study the radiative feedback of absorbing aerosols. The control simulation consists of aerosol transport with no feedback. Experiment 1 considers anthropogenic aerosols (BC, organic carbon and sulphate), while experiment two considers only carbonaceous aerosols (BC and OC). An extensive evaluation of the model performance has been carried out. The BC columnar burden is found to be the highest over the Indo-Gangetic basin in every season with an average value varying between 0.9 to 2.6 mg/m². A second set of experiments is carried out to understand the relative contribution of various individual sectors to BC loading and transport at regional scale. This simulations follow 'subtraction' method, where emission from one sector is removed and the difference with experiment 1 is attributed to the relative share of that particular sector. Our results will provide a comprehensive idea about BC loading and transport from various sectors in India that will be useful in framing policy to mitigate climate change.

Keywords: RegCM4, BC burden, anthropogenic aerosols

Acknowledgement: DST Inspire Fellowship, IIT Delhi