Air pollution forms at night? – Featured

February 07, 2023

In large cities, air pollution is largely composed of gases and suspended particles. Better understanding how this air contamination is formed and what chemical mechanisms come into play is essential to prevent it. A British team has studied the impact of a nocturnal atmospheric oxidant.

Smog is a pollution fog that develops in urban areas, most often in large megalopolises. He “forms in the air when strong sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs)”, explains the government of New Brunswick in Canada. These substances, produced in part by human activity, degrade in the atmosphere and contribute to disturbing its chemical balances. Among them, “butane, toluene, ethanol, acetone or even benzene found in industry, most often in the form of organic solvents (for example, in paints or inks)”describes the French Environment and Energy Management Agency (Ademe).

Nocturnal pollution on the rise

What are the mechanisms linked to the formation of pollution? According to researchers at the University of Birmingham, nitrogen trioxide, or nitrate radical (NO3), is to blame. This oxidant would form essentially during the night.

Their work showed that the level of this gas was on the rise in 8 major Chinese cities: Beijing, Shanghai, Guangzhou, Chengdu, Xi’an, Jinan, Zhengzhou and Shijiazhuang. reaching a degree “equivalent to that of Los Angeles in the 1990s, and continuing an upward trend”, note the authors. Even though it is falling in the metropolises of rich countries. This is a reason for concern for the environment and health in China as in India. Two countries which concentrate huge megalopolises.

Reduce VOC emissions

“The nocturnal oxidation process is a poorly understood chemical reaction, which we absolutely must shed light on if we are to formulate effective strategies against air pollution”, say the scientists. However, they already believe that reducing VOC emissions could help reduce air pollution, day and night.

  • Source : University of Birmigham – Atmospheric Research Volumes 164–165, 1 October–1 November 2015, Pages 347-357 – Ademe – gouvernement du New Brunswick au Canada

  • Written by : Dominique Salomon – Edited by: Emmanuel Ducreuzet

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