Exploring the causes for co-pollution of O3 and PM2.5 in summer over North China

Environ Monit Assess. 2022 Mar 21;194(4):289. doi: 10.1007/s10661-022-09951-4.

Abstract

Co-pollution of surface O3 and PM2.5 has become the most predominant type of air pollutions in Beijing-Tianjin-Hebei region in the hot season since 2017, particularly in May-July. Analysis based on observational data showed that co-pollution was always accompanied by high temperature, moderate relative humidity, extremely high SO2, and higher NO2. We also found that the meteorology and precursor dependence of O3 was similar between co-pollution and O3- single pollution. While PM2.5 in co-pollution was more related to temperature, relative humidity, and precursors, that in PM2.5-singe pollution were more related to small winds. These results indicate that co-pollution seemed to be more affected by atmospheric chemistry. According to the PM2.5 components, secondary inorganic aerosols (SIA) composed 44.3-48.7% of PM2.5 in co-pollution, while those accounting for 42.1-46.5% and 41.2-44.3%, respectively, in O3- and PM2.5-single pollution, which further confirmed the relatively stronger atmospheric chemistry processes in co-pollution. And the high proportion of SIA in co-pollution was mainly attributed to SO42-, which was observed to rapidly boom in non-refractory submicron aerosol (NR-PM1) on the condition of high level of O3 at daytime. Additionally, we further explored the interactions of O3 and PM2.5 in co-pollution. It was found that most (~61.9%) co-pollution episodes were initiated by high O3 at daytime; while for other episodes, high PM2.5 firstly occurred under the more stable meteorological conditions, and then accumulation of precursors further induced high O3. A higher SIA concentration was observed in O3-initiated co-pollution, indicating that the atmospheric oxidation in co-pollution caused by chemical processes was stronger than that by physical processes, which was further approved by the higher values of SOR and NOR in O3-initiated co-pollution. This observational study revealed that controlling O3 and precursor SO2 is the key to abating co-pollution in the hot season.

Keywords: Co-pollution; High level of oxidation products; Meteorology; Precursors; Surface O3 and PM2.5.

Publication types

  • Observational Study

MeSH terms

  • Air Pollutants* / analysis
  • China
  • Environmental Monitoring / methods
  • Particulate Matter / analysis
  • Seasons

Substances

  • Air Pollutants
  • Particulate Matter