Air Pollution and Air Oxidation: A Revealing Study

Air pollution is a serious environmental problem that affects the health and well-being of millions of people around the world. One of the key factors that influence air pollution is atmospheric oxidation, which is the process by which pollutants are transformed into secondary pollutants and eventually removed from the atmosphere.

A recent study by researchers from the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences has revealed the relationship between air oxidation and air pollution in Lanzhou, a city in northwest China that suffers from frequent haze episodes. The study was published in Science of the Total Environment on Dec. 30, 2023.

The researchers used empirical equations to estimate the emission of primary pollutant particles and the formation of secondary pollutant particles in the atmosphere, and analyzed the change characteristics of major atmospheric oxidants, such as ozone (O3) and nitrogen dioxide (NO2), in Lanzhou. They also explored the possible causes of the change in pollutant source and concentration in heavily polluted weather, and elucidated the mechanism of atmospheric oxidation affecting the secondary formation of atmospheric particles.

The results show that atmospheric oxidation has a threshold effect on the secondary formation of atmospheric particles. When the concentration of atmospheric oxidant is low (MDA8 O3 ≤100μg/m3), the oxidation process of atmospheric volatile organic compounds (VOCs) is easier to achieve, thus generating more secondary aerosols and promoting the formation of secondary particles. When the concentration of atmospheric oxidant is higher than 160μg/m3, the proportion of secondary particulate matter is lower than that of primary particulate matter.

The total oxidant agent Ox (Ox=O3+NO2) is negatively correlated with the sulfur oxidation rate and nitrogen oxidation rate, indicating that the formation rate of sulfur dioxide (SO2) and nitric oxide (NO) is inhibited by the high concentration of Ox. The high-pressure ridge over Lanzhou was maintained for a long time, which reduced the surface wind speed and weakened the transport and diffusion of pollutants near the surface.

The researchers found that the PM2.5 (particulate matter with a diameter less than 2.5 micrometers) in Lanzhou’s atmosphere is mainly from the Hexi Corridor area, and the PM10 (particulate matter with a diameter less than 10 micrometers) is mainly from the southeast of Lanzhou. PM2.5 and PM10 are both harmful to human health and can cause respiratory and cardiovascular diseases.

This study deepens the understanding of atmospheric oxidation affecting the formation mechanism of air pollution, and provides a reference for the prevention and control of air pollution and the improvement of air quality in Lanzhou.

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