La pollution de l’air est un problème environnemental grave et croissant qui affecte la santé et le bien-être des personnes et des écosystèmes partout dans le monde. La pollution de l’air contribue à une gamme de problèmes de santé, notamment les maladies respiratoires, les maladies cardiaques et les accidents vasculaires cérébraux, et peut également endommager les cultures, les forêts et les plans d’eau.
Une étude récente a révélé que la Chine est une Source majeure de radicaux nitrates (PNO3) pendant la nuit, ce qui pourrait affecter de manière significative les niveaux d’ozone et de particules fines (PM2.5) dans l’atmosphère.
L’étude a révélé que la Chine a connu une forte augmentation de la production de NO3 pendant les heures de nuit, tandis que l’Europe et les États-Unis ont connu une diminution. Cette augmentation devrait entraîner des conséquences importantes sur la pollution de l’air pour la Chine et d’autres pays en développement, comme l’Inde.
Production actuelle de NO3 radicaux dans huit villes chinoises représentatives – Pékin, Shanghai, Guangzhou, Chengdu, Xi’an, Jinan, Zhengzhou et Shijiazhuang – est comparable à celle de Los Angeles dans les années 1990, mais avec une tendance générale à la hausse.
Publication de leurs découvertes dans la revue University of Birmingham – believes that the long-term decreasing trend in the production of NO3 in Los Angeles offers hope that the level of nocturnal ozone can be reduced while simultaneously reducing nitrogen oxides.
Co-author Professor Zongbo Shi, from the University of Birmingham, commented: “Nitrogen oxides derived from combustion and natural sources are reactive gases that regulate the formation of key air pollutants including both ozone (O3) and PM2.5. Nocturnal oxidation driven by nitrate radicals is an important, but poorly understood, process in atmospheric chemistry – we must understand this better, if we are to formulate effective global pollution mitigation strategies and understand the influence of nitrogen oxides on air quality and climate.”
The study shows that, if recent increasing ozone pollution trends continue, nighttime oxidation in China will increase further even if NOx emissions are reduced. However, based on the trend in Los Angeles since 1980 and global changes since the COVID-19 lockdown, scientists believe that, currently, reducing the emissions of volatile organic compounds (VOC) would simultaneously reduce daytime ozone and nighttime oxidation in China and similar regions.
Night-time NO3 chemistry influences next-day photochemistry by removing nitrogen oxides and VOCs – enhancing ozone formation. The production of NO3 radicals increased significantly in three megacity clusters (North China Plain, Yangtze River Delta, and Pearl River Delta), with experts suggesting that the hotspot of NO3 chemistry persists for the entire year in China.
Given that much lower values of NO3 radicals in both the Europe and the United States have been shown to exert significant impacts on particulate nitrate and organic aerosol formation in those regions, the researchers believe that NO3 radical chemistry may play a more critical role in atmospheric oxidation and aggravate both O3 and PM2.5 pollution in China in the near future.
Increased O3 and PM2.5 pollution due to nighttime oxidation poses an important challenge in further improving air quality in China, with significant public health implications.
Reference: “Increased night-time oxidation over China despite widespread decrease across the globe” by Haichao Wang, Haolin Wang, Xiao Lu, Keding Lu, Lin Zhang, Yee Jun Tham, Zongbo Shi, Kenneth Aikin, Shaojia Fan, Steven S. Brown and Yuanhang Zhang, 26 January 2023, Nature Geoscience.
DOI: 10.1038/s41561-022-01122-x
Tags: côté obscur pollution atmosphérique Chine
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