Characterizing primary dicarboxylic acid emissions from biomass burning in China: Fuel-Specific signatures and...

Low-molecular-weight dicarboxylic acids and related compounds (LWDCs) are key components of organic aerosols, yet their primary emissions from biomass burning (BB) remain poorly understood. This study quantified the emission characteristics of 14 target LWDCs from the burning of five representative Chinese biomass (rice straw, sugarcane residues, pine, eucalyptus, and cedar) under controlled laboratory conditions. The results identified pine burning as a strong source, with a total emission factor (EF) of 474 ± 189 mg kg^-1, nearly an order of magnitude higher than those of crop residues. While oxalic acid (C₂) was the predominant dicarboxylic acid, dicarbonyls (glyoxal and methylglyoxal) unexpectedly dominated the total mass (56%-76%), highlighting a vast reservoir of reactive precursors in nascent plumes. LWDC EFs exhibited a significant inverse correlation with modified combustion efficiency (MCE; p < 0.05), indicating that smoldering-dominated regimes enhance organic acid release through devolatilization. By integrating laboratory-derived EFs with satellite-constrained fire radiative power (FRP) data, we estimated China's annual primary LWDC emissions from BB from 2016 to 2024, which ranged from 9.9 to 15.3 Gg. Woody BB emerged as the primary contributor, accounting for 50%-57% of the national budget. A sharp trend in emissions observed post-2022 reflected the compounded impacts of climatic events and land-management practices. These findings provide critical experimental data for refining emission inventories and offer a scientific basis for targeted air quality mitigation strategies.