Organic carbon health burden in the Indo-Gangetic Plain: Exposures, risks, and mitigation

Organic carbon (OC) aerosols are complex carbon-containing particles suspended in the atmosphere. OC accounts for a large fraction of atmospheric aerosol and significantly affects air quality, atmospheric chemistry, human health, and climate forcing. This study focuses on assessing the specific influence of OC aerosols on public health within the Indo-Gangetic Plain (IGP). The assessment was done with an efficiently modeled OC distribution in a fine-resolved chemistry-transport model, CHIMERE, using the Weather Research and Forecasting (WRF) model as the meteorological driver in the offline mode. Simulations are carried out at a horizontal resolution of 0.1^◦×0.1^◦ over the IGP domain (20^oN to 30.9^oN and 75^oE to 89.3^oE). The health assessment was done for the seasonal mean of winter (January, February, November and December) OC concentration.

Higher OC concentrations were consistently observed across diverse area types in the IGP: Megacity (Kolkata and Delhi), Urban (Agra, Varanasi, Kanpur), and Semiurban (Kharagpur). Wintertime OC concentrations were significantly higher than the established Theoretical Threshold Limit (TTL) of 16 μg m^-3. OC all-day (daytime) concentrations exceeded 60 (30) μg m^-3, which is about 4 (2) times the TTL, in urban and megacity areas. Over 95% of the populations in semi-urban, urban, and megacity areas are exposed to OC concentrations above the threshold, with rural and semi-rural populations also experiencing substantial exposure. Relative risk (RR) and Cardiovascular Mortality (CVM) associated with OC exposure during the winter months were assessed to evaluate the health impacts. RR values consistently exceed one across the IGP, indicating potential health risks associated with wintertime OC exposure. The burden of CVM attributable to OC is estimated to encompass approximately 2,00,000 annual deaths across the entire IGP. The CVM attributable to OC in comparison to both PM_2.5 and BC was found to be about 1.5 times higher over Agra and Kanpur. This underscores the need for immediate policy interventions to address elevated OC concentrations in the IGP, especially in high-risk areas like Agra and Kanpur, mitigating the significant burden of CVM associated with wintertime OC exposure.