Brown Carbon Light Absorption over India: Research Status and Need for Discerning Climate Impacts

Brown carbon (BrC) absorbs solar radiation and influences the regional and global climate. A major pollutant in India, BrC absorption has received reasonable research attention, with studies focusing on spatial-temporal variability and emission sources. By synthesizing the available literature, this paper presents the current research status on the topic and identifies gaps that need to be addressed to better understand the climate impacts of BrC in India. In terms of the measurement of BrC light absorption, we find that the solvent extraction technique is the most commonly used, followed by the Ångström exponent extrapolation and the component subtraction techniques. Measurement sites are concentrated in the Indo-Gangetic plains, which show significantly higher absorption levels than other regions. Seasonal variability shows increased absorption during postmonsoon and winter periods, particularly in peninsular India. Though limited in number, studies on emission sources identify biomass burning and vehicular emissions as key contributors. In terms of radiative impact, assessments from the Indo-Gangetic plains suggest that BrC contributes substantially to direct radiative effects, potentially accounting for a net 31–48% warming. Global climate models assign a net forcing of 0.5–2 W m^–2 over India; however, they rely on parametrizations derived from non-Indian locations and sources, which may not accurately represent BrC over India. Overall, expanded spatial coverage, diverse source characterization, and improved radiative effect estimations are key to decoding BrC’s climate impact in India and globally.

Brown carbon aerosols are abundant over India and likely influence the climate. This perspective reviews their sources and spatiotemporal variability, highlighting key gaps and priorities for future research.