Abstract
Fast atmospheric particulate nitrate and sulfate formation under high-humidity conditions has been extensively observed; however, the underlying chemical mechanisms and their relative contributions remain poorly understood. This study examined the characteristic high-humidity events (HHEs) in southern China during spring, providing field observation evidence for the crucial role of NO2-driven multiphase reactions in particulate nitrate and sulfate formation. Our findings revealed efficient nitrate formation during early HHEs, likely facilitated by enhanced NO2 uptake via disproportionation reaction. As humidity increased and fog formed, S(IV) oxidation competitively consumed NO2 and N(III), causing rapid sulfate formation. The resulting N(III), produced from the oxidation of S(IV) by NO2 (aq), further oxidizes S(IV) effectively in droplets due to its slow liquid-gas mass transfer rate. A state-of-the-art multiphase box model demonstrated that NO2 uptake and SO2 oxidation by NO2/N(III) represent dominant formation pathways during HHEs, accounting for 45.4% and 63.6% of the total nitrate and sulfate production, respectively. These results highlight the critical importance of NO2-driven multiphase chemistry in particulate pollution under high-humidity environments.
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Data availability
Observed data and data analysis methods are available on request from Jinsheng Chen (jschen@iue.ac.cn).
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Acknowledgements
This work was funded by the National Natural Science Foundation of China (U22A20578), the guiding project of seizing the commanding heights of “self-purifying city” (IUE-CERAE-202402), the National Key Research and Development Program (2022YFC3700304), STS Plan Supporting Project of the Chinese Academy of Sciences in Fujian Province (2023T3013), and Xiamen Atmospheric Environment Observation and Research Station of Fujian Province.
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Z.L. contributed to the methodology, data curation, software, analysis and writing of the original draft. L.X. and J.C. contributed to the conceptualization, investigation, data curation, reviewing and editing the text, supervision, and funding acquisition. X.T., G.C., C.Y., K.Z., F.Z., L.L., and Y.C. provided useful advice and revised the manuscript.
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Lin, Z., Ji, X., Xu, L. et al. Enhanced NO2-driven multiphase formation of particulate nitrate and sulfate under high-humidity conditions. npj Clim Atmos Sci (2026). https://doi.org/10.1038/s41612-026-01352-5
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DOI: https://doi.org/10.1038/s41612-026-01352-5
