Abstract
Abstract. This study examines differences in the surface black carbon (BC) aerosol loading between the Bay of Bengal (BoB) and the Arabian Sea (AS) and identifies dominant sources of BC in South Asia and surrounding regions during March–May 2006 (Integrated Campaign for Aerosols, Gases and Radiation Budget, ICARB) period. A total of 13 BC tracers are introduced in the Weather Research and Forecasting Model coupled with Chemistry to address these objectives. The model reproduced the temporal and spatial variability of BC distribution observed over the AS and the BoB during the ICARB ship cruise and captured spatial variability at the inland sites. In general, the model underestimates the observed BC mass concentrations. However, the model–observation discrepancy in this study is smaller compared to previous studies. Model results show that ICARB measurements were fairly well representative of the AS and the BoB during the pre-monsoon season. Elevated BC mass concentrations in the BoB are due to 5 times stronger influence of anthropogenic emissions on the BoB compared to the AS. Biomass burning in Burma also affects the BoB much more strongly than the AS. Results show that anthropogenic and biomass burning emissions, respectively, accounted for 60 and 37% of the average ± standard deviation (representing spatial and temporal variability) BC mass concentration (1341 ± 2353 ng m−3) in South Asia. BC emissions from residential (61%) and industrial (23%) sectors are the major anthropogenic sources, except in the Himalayas where vehicular emissions dominate. We find that regional-scale transport of anthropogenic emissions contributes up to 25% of BC mass concentrations in western and eastern India, suggesting that surface BC mass concentrations cannot be linked directly to the local emissions in different regions of South Asia.
Highlights
Black carbon (BC), a byproduct of incomplete combustion, is a key atmospheric aerosol species because it contributes largely to the climate forcing (e.g., Ramanathan and Carmichael, 2008; Wang et al, 2014; Hodnebrog et al, 2014) and, along with other fine particulates, adversely affects human health (e.g., Dockery and Stone, 2007)
This study implemented source, sector- and region-specific BC tracers in the WRF-Chem model to understand the differences in BC loadings between the Bay of Bengal and the Arabian Sea and assess the relative importance of different BC sources in South Asia during March–May 2006
The model reproduced the temporal and spatial variability of BC distribution observed during the ICARB ship cruise
Summary
Black carbon (BC), a byproduct of incomplete combustion, is a key atmospheric aerosol species because it contributes largely to the climate forcing (e.g., Ramanathan and Carmichael, 2008; Wang et al, 2014; Hodnebrog et al, 2014) and, along with other fine particulates, adversely affects human health (e.g., Dockery and Stone, 2007). Large emissions of BC in South Asia lead to BCinduced radiative perturbation which is significantly higher than the globally averaged estimates (Babu et al, 2004; Ramanathan and Carmichael, 2008). The relative contributions of different emission sources to atmospheric BC mass concentrations are still unknown for South Asia, except for the Delhi region where the majority of the atmospheric BC is attributed to emissions from transportation (∼ 59 %) and domestic (∼ 32 %) sectors (Marrapu et al, 2014). In the Results section, we first evaluate the model performance and quantify the contribution of different emission sources and sectors to total BC loading and demonstrate the importance of regional transport in distribution of BC in the atmosphere of South Asia
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