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Biomass burning is a major source of carbonaceous aerosols that significantly influences the Earth's radiation balance. However, the spectral light absorption properties of biomass burning aerosols (BBAs), particularly the contribution of brown carbon (BrC), remain poorly constrained due to reliance on laboratory measurements that may not accurately represent real-world atmospheric conditions. To address this limitation, we developed an unmanned aerial vehicle (UAV) based-platform for direct in-situ measurements of BBAs in the ambient atmosphere over the rural North China Plain. This approach reduces biases inherent to laboratory chamber experiments and enables a more realistic characterization of BBAs absorption properties. Our measurements revealed that the absorption & Aring;ngstr & ouml;m exponent (AAE) for typical residential biomass burning was 3.70 +/- 0.04 under smoldering conditions and 1.50 +/- 0.08 under flaming conditions. Variations in AAE were driven primarily by combustion conditions and smoke humidity rather than fuel type. Additionally, field-observed OC/EC ratios were up to ten times higher than those reported in laboratory chamber studies, resulting in systematically lower mass absorption cross-sections. This finding suggests that the BBAs light absorption and radiative forcing estimates in the North China Plain may be systematically overestimated by chamber-based studies. Notably, under smoldering conditions, BrC absorption at 375 nm was up to 6.6 times greater than that of black carbon (BC) once mass emissions are considered, emphasizing that strategies aiming at reducing smoldering combustion could be particularly effective in mitigating the ultraviolet radiative effects of BBAs. Our results demonstrate that ambient atmospheric measurements are essential for accurately constraining BBAs absorption properties and their climate impacts.

来源平台：SCIENCE CHINA-EARTH SCIENCES