| 12 Jan 2026
Light Absorption Properties and Composition of Brown carbon in North China Plain: Implication for an Enhancing Role of Nitrogenous Organic Compounds
Abstract. Brown carbon (BrC), an efficiently light-absorbing carbonaceous aerosol, exerts significant impacts on the global energy budget and regional climate, attracting growing scientific attention. To advance understanding of the spatial variability of atmospheric BrC and its dominant formation pathways in the North China Plain (NCP), light absorption properties, chemical composition and formation process of the water-soluble BrC in 2023 winter were investigated by conducting simultaneous measurements at five sites across the NCP, namely, Beijing, Tianjin, Luancheng (rural site), Handan and Jinan. Our results showed that the average light absorption coefficient at 365 nm (abs365) in Luancheng was approximately 1.1–3.5 times higher than those in urban ones; While mass absorption efficiency displayed a distinctly different spatial pattern, with the strongest light-absorptivity (1.40 ± 0.02 m2 g−1) recorded in Jinan. Notably, average abs365 in four urban sites exhibited a decline of ~ 45 % from 2018 to 2023 compared to those previous observations. Furthermore, the light-absorptivity of BrC was enhanced from clean to haze period at the most sampling sites along with the increasing N:C ratio, indicating that nitrogenous organic compounds (NOCs) were the important BrC chromophores in the NCP. Additionally, more than 50 % of NOCs were confirmed to be secondarily formed; and the ammonia-driven aqueous reactions were identified as the predominant pathway governing the secondary formation of these NOCs. These results elucidate the substantial contribution of NOCs to atmospheric BrC in the NCP, and further confirm the importance of ammonia emission for alleviating haze and BrC pollution in this region.
This manuscript presents a comprehensive multi-site wintertime dataset of water-soluble brown carbon (BrC) across the North China Plain (NCP). By combining optical measurements, molecular markers, PMF source apportionment, and statistical (random forest) analysis, the authors argue that nitrogen-containing organic compounds (NOCs), largely formed via ammonia-driven aqueous chemistry, play a dominant role in BrC light absorption during haze events. The dataset is extensive, spatially representative, and timely. The topic is of high relevance to atmospheric chemistry, particularly given increasing attention to ammonia-rich environments and nitrogen-dominated BrC absorption. The manuscript is generally well written and technically competent, and many results are consistent with recent literature. However, several key conclusions are currently overstated, and important methodological assumptions require stronger justification or sensitivity analysis. I therefore recommend major revision before the manuscript can be considered for publication.
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