Urban black-carbon radiative heating intensified by biogenic-anthropogenic interactions

Black carbon (BC) is a global climate forcer due to its strong radiative absorption, which is highly sensitive to coating formation regulated by anthropogenic and biogenic emissions across regions. However, how cross-regional biogenic sources modulate BC coating formation and radiative effects, particularly in high anthropogenic emission environments, remains poorly understood. Here we show, using integrated observations and model simulations, that biogenic volatile organic compounds from vegetation-rich regions undergo atmospheric oxidation to produce oxygenated organic compounds, which are subsequently advected into downwind urban areas. These products enhance regional atmospheric oxidation capacity and supply additional precursors, thereby promoting secondary organic aerosol production. This biogenic-induced strengthening of regional photochemistry significantly drives the formation of highly oxidized secondary organic aerosol coatings on BC particles and increases its fraction within the total particle population. Consequently, BC absorption efficiency increases more steeply with the coating carbon oxidation state under biogenic-rich conditions, yielding an average ~20% enhancement in radiative absorption from the lensing effect relative to biogenic-poor periods. Our findings reveal that cross-regional biogenic-anthropogenic interactions enhance both the formation and particle population fraction of secondary organic aerosol coatings on urban BC, potentially further amplifying its radiative effects as biogenic emissions increase under future warming scenarios.