{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,15]],"date-time":"2026-07-15T19:02:58Z","timestamp":1784142178614,"version":"3.55.0"},"reference-count":67,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T00:00:00Z","timestamp":1753833600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100012166","name":"National Key Research and Development Program of China","doi-asserted-by":"publisher","award":["2023YFC3709201"],"award-info":[{"award-number":["2023YFC3709201"]}],"id":[{"id":"10.13039\/501100012166","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Toxics"],"abstract":"<jats:p>Understanding the differential impacts of emission sources of volatile organic compounds (VOCs) on formaldehyde (HCHO) levels is pivotal to effectively mitigating key photochemical radical precursors, thereby enhancing the regulation of atmospheric oxidation capacity (AOC) and ozone formation. This investigation systematically selected and analyzed year-long VOC measurements across three urban zones in Shenzhen, China. Photochemical age correction methods were implemented to develop the initial concentrations of VOCs before source apportionment; then Positive Matrix Factorization (PMF) modeling resolved six primary sources: solvent usage (28.6\u201347.9%), vehicle exhaust (24.2\u201331.2%), biogenic emission (13.8\u201318.1%), natural gas (8.5\u201316.3%), gasoline evaporation (3.2\u20138.9%), and biomass burning (0.3\u20132.4%). A machine learning (ML) framework incorporating Shapley Additive Explanations (SHAP) was subsequently applied to evaluate the influence of six emission sources on HCHO concentrations while accounting for reaction time adjustments. This machine learning-driven nonlinear analysis demonstrated that vehicle exhaust nearly always emerged as the primary anthropogenic contributor in diverse functional zones and different seasons, with gasoline evaporation as another key contributor, while the traditional reactivity metric method, ozone formation potential (OFP), tended to underestimate the role of the two sources. This study highlights the primacy of strengthening emission reduction of transportation sectors to mitigate HCHO pollution in megacities.<\/jats:p>","DOI":"10.3390\/toxics13080643","type":"journal-article","created":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T16:09:27Z","timestamp":1753891767000},"page":"643","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Decoding the Primacy of Transportation Emissions of Formaldehyde Pollution in an Urban Atmosphere"],"prefix":"10.3390","volume":"13","author":[{"given":"Shi-Qi","family":"Liu","sequence":"first","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hao-Nan","family":"Ma","sequence":"additional","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Meng-Xue","family":"Tang","sequence":"additional","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yu-Ming","family":"Shao","sequence":"additional","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ting-Ting","family":"Yao","sequence":"additional","affiliation":[{"name":"Shenzhen Academy of Metrology and Quality Inspection, Shenzhen 518107, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ling-Yan","family":"He","sequence":"additional","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiao-Feng","family":"Huang","sequence":"additional","affiliation":[{"name":"Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen 518055, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"862","DOI":"10.1016\/j.scitotenv.2018.07.411","article-title":"Summertime high resolution variability of atmospheric formaldehyde and non-methane volatile organic compounds in a rural background area","volume":"647","author":"Navazo","year":"2019","journal-title":"Sci. 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