Haze Occurrence Caused by High Gas-to-Particle Conversion in Moisture Air under Low Pollutant Emission in a Megacity of China

Qingxia Ma; Weisi Wang; Dexin Liu; Rongke Zhao; Jingqi Zhao; Wanlong Li; Yanfang Pan; Daizhou Zhang

doi:10.3390/ijerph19116405

Haze Occurrence Caused by High Gas-to-Particle Conversion in Moisture Air under Low Pollutant Emission in a Megacity of China

Int J Environ Res Public Health. 2022 May 25;19(11):6405. doi: 10.3390/ijerph19116405.

Authors

Qingxia Ma^{1

2}, Weisi Wang³, Dexin Liu¹, Rongke Zhao⁴, Jingqi Zhao¹, Wanlong Li¹, Yanfang Pan¹, Daizhou Zhang⁵

Affiliations

¹ 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.
² Henan Key Laboratory of Integrated Air Pollution Control and Ecological Security, Kaifeng 475004, China.
³ Henan Ecological and Environmental Monitoring Center, Zhengzhou 450007, China.
⁴ Henan Kaifeng College of Science Technology and Communication, Kaifeng 475004, China.
⁵ Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto 862-8502, Japan.

Abstract

Haze occurred in Zhengzhou, a megacity in the northern China, with the PM_2.5 as high as 254 μg m^-3 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_2.5) between 5-26 December were investigated to explore the reasons for the haze occurrence. Results show that the haze was caused by efficient SO₂-to-suflate and NO_x-to-nitrate conversions under high relative humidity (RH) condition. In comparison with the period before the restriction (5-18 December) when the PM_2.5 was low, the concentration of PM_2.5 during the haze (19-26 December) was 173 µg m^-3 on average with 51% contributed by sulfate (31 µg m^-3) and nitrate (57 µg m^-3). The conversions of SO₂-to-sulfate and NO_x-to-nitrate efficiently produced sulfate and nitrate although the concentration of the two precursor gases SO₂ and NO_x 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.

Keywords: emission restriction; gas-to-particle conversion; haze; high RH; urban pollution.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aerosols / analysis
Air Pollutants* / analysis
Air Pollution* / analysis
China
Environmental Monitoring / methods
Environmental Pollutants*
Nitrates / analysis
Nitrogen Oxides / analysis
Particulate Matter / analysis
Seasons
Sulfates / analysis
Water / chemistry

Substances

Aerosols
Air Pollutants
Environmental Pollutants
Nitrates
Nitrogen Oxides
Particulate Matter
Sulfates
Water

Grants and funding

This research was funded by Natural Science Foundation of China (42105071) and project of science and technology of the Henan province for tackling key problems (212102110390). D. Zhang was supported by the KAKENHI (No. 21H01158) of the JSPS.