{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,23]],"date-time":"2026-09-23T04:55:27Z","timestamp":1790139327507,"version":"4.0.1"},"reference-count":57,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2022,5,25]],"date-time":"2022-05-25T00:00:00Z","timestamp":1653436800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"Natural Science Foundation of China","doi-asserted-by":"publisher","award":["42105071"],"award-info":[{"award-number":["42105071"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"Natural Science Foundation of China","doi-asserted-by":"publisher","award":["212102110390"],"award-info":[{"award-number":["212102110390"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"Natural Science Foundation of China","doi-asserted-by":"publisher","award":["21H01158"],"award-info":[{"award-number":["21H01158"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"name":"project of science and technology of the Henan province for tackling key problems","award":["42105071"],"award-info":[{"award-number":["42105071"]}]},{"name":"project of science and technology of the Henan province for tackling key problems","award":["212102110390"],"award-info":[{"award-number":["212102110390"]}]},{"name":"project of science and technology of the Henan province for tackling key problems","award":["21H01158"],"award-info":[{"award-number":["21H01158"]}]},{"DOI":"10.13039\/501100001691","name":"KAKENHI","doi-asserted-by":"publisher","award":["42105071"],"award-info":[{"award-number":["42105071"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"KAKENHI","doi-asserted-by":"publisher","award":["212102110390"],"award-info":[{"award-number":["212102110390"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"KAKENHI","doi-asserted-by":"publisher","award":["21H01158"],"award-info":[{"award-number":["21H01158"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJERPH"],"abstract":"<jats:p>Haze occurred in Zhengzhou, a megacity in the northern China, with the PM2.5 as high as 254 \u03bcg m\u22123 on 25 December 2019, despite the emergency response measure of restriction on the emission of anthropogenic pollutants which was implemented on December 19 for suppressing local air pollution. Air pollutant concentrations, chemical compositions, and the origins of particulate matter with aerodynamic diameter smaller than 2.5 \u00b5m (PM2.5) between 5\u201326 December were investigated to explore the reasons for the haze occurrence. Results show that the haze was caused by efficient SO2-to-suflate and NOx-to-nitrate conversions under high relative humidity (RH) condition. In comparison with the period before the restriction (5\u201318 December) when the PM2.5 was low, the concentration of PM2.5 during the haze (19\u201326 December) was 173 \u00b5g m\u22123 on average with 51% contributed by sulfate (31 \u00b5g m\u22123) and nitrate (57 \u00b5g m\u22123). The conversions of SO2-to-sulfate and NOx-to-nitrate efficiently produced sulfate and nitrate although the concentration of the two precursor gases SO2 and NOx was low. The high RH, which was more than 70% and the consequence of artificial water-vapor spreading in the urban air for reducing air pollutants, was the key factor causing the conversion rates to be enlarged in the constriction period. In addition, the last 48 h movement of the air parcels on 19\u201326 December was stagnant, and the air mass was from surrounding areas within 200 km, indicating weather conditions favoring the accumulation of locally-originated pollutants. Although emergency response measures were implemented, high gas-to-particle conversions in stagnant and moisture circumstances can still cause severe haze in urban air. Since the artificial water-vapor spreading in the urban air was one of the reasons for the high RH, it is likely that the spreading had unexpected side effects in some certain circumstances and needs to be taken into consideration in future studies.<\/jats:p>","DOI":"10.3390\/ijerph19116405","type":"journal-article","created":{"date-parts":[[2022,5,25]],"date-time":"2022-05-25T05:12:27Z","timestamp":1653455547000},"page":"6405","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Haze Occurrence Caused by High Gas-to-Particle Conversion in Moisture Air under Low Pollutant Emission in a Megacity of China"],"prefix":"10.3390","volume":"19","author":[{"given":"Qingxia","family":"Ma","sequence":"first","affiliation":[{"name":"Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng 475004, China"},{"name":"Henan Key Laboratory of Integrated Air Pollution Control and Ecological Security, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Weisi","family":"Wang","sequence":"additional","affiliation":[{"name":"Henan Ecological and Environmental Monitoring Center, Zhengzhou 450007, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8471-0912","authenticated-orcid":false,"given":"Dexin","family":"Liu","sequence":"additional","affiliation":[{"name":"Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rongke","family":"Zhao","sequence":"additional","affiliation":[{"name":"Henan Kaifeng College of Science Technology and Communication, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jingqi","family":"Zhao","sequence":"additional","affiliation":[{"name":"Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wanlong","family":"Li","sequence":"additional","affiliation":[{"name":"Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6918-0511","authenticated-orcid":false,"given":"Yanfang","family":"Pan","sequence":"additional","affiliation":[{"name":"Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng 475004, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Daizhou","family":"Zhang","sequence":"additional","affiliation":[{"name":"Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862-8502, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,5,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1126\/sciadv.1601530","article-title":"Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China","volume":"2","author":"Cheng","year":"2016","journal-title":"Sci. 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