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.
Henan Key Laboratory of Integrated Air Pollution Control and Ecological Security, Kaifeng 475004, China.
Int J Environ Res Public Health. 2022 May 25;19(11):6405. doi: 10.3390/ijerph19116405.
Haze occurred in Zhengzhou, a megacity in the northern China, with the PM as high as 254 μg m 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 µm (PM) between 5-26 December were investigated to explore the reasons for the haze occurrence. Results show that the haze was caused by efficient SO-to-suflate and NO-to-nitrate conversions under high relative humidity (RH) condition. In comparison with the period before the restriction (5-18 December) when the PM was low, the concentration of PM during the haze (19-26 December) was 173 µg m on average with 51% contributed by sulfate (31 µg m) and nitrate (57 µg m). The conversions of SO-to-sulfate and NO-to-nitrate efficiently produced sulfate and nitrate although the concentration of the two precursor gases SO and NO 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 19-26 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.
2019 年 12 月 25 日，中国北方大城市郑州出现雾霾，PM2.5 高达 254μg/m3，尽管 19 日已实施限制人为污染物排放的应急措施以抑制当地空气污染，但仍未能阻止雾霾发生。本研究于 2019 年 12 月 5 日至 26 日调查了污染物浓度、化学成分以及空气动力学直径小于 2.5μm 的颗粒物（PM）的来源，以探讨雾霾发生的原因。结果表明，高相对湿度（RH）条件下，SO2向硫酸盐和 NOx向硝酸盐的高效转化是导致雾霾形成的主要原因。与限制排放前（12 月 5 日至 18 日）PM 较低的时期相比，雾霾期间（12 月 19 日至 26 日）的 PM 平均浓度为 173μg/m3，其中硫酸盐（31μg/m3）和硝酸盐（57μg/m3）分别占 51%。尽管 SO2和 NOx 两种前体气体浓度较低，但 SO2向硫酸盐和 NOx 向硝酸盐的高效转化仍产生了硫酸盐和硝酸盐。高 RH（超过 70%）是限制期间转化率增大的关键因素，这是城市空气中人工水汽扩散以降低空气污染物浓度的结果。此外，19 日至 26 日的空气团在过去 48 小时内处于停滞状态，气团来自 200km 范围内的周边地区，表明天气条件有利于本地污染物的积累。尽管实施了应急措施，但在停滞和潮湿的条件下，高气体到颗粒的转化仍可能导致城市空气中出现严重的雾霾。由于城市空气中的人工水汽扩散是 RH 升高的原因之一，因此在某些特定情况下，这种扩散可能会产生意想不到的副作用，这需要在未来的研究中加以考虑。
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