Abstract
Air pollution in Chinese megacities has reached extremely hazardous levels, and human activities are responsible for the emission or production of large amounts of particulate matter (PM). In addition to PM from anthropogenic sources, natural phenomena, such as dust storms over Asian deserts, may also emit large amounts of PM, which lead episodically to poor air quality over Chinese megacities. In this paper, we quantify the degradation of air quality by dust over Beijing, Chengdu and Shanghai megacities using the three dimensions (3D) chemistry transport model CHIMERE, which simulates dust emission and transport online. In the first part of our work, we evaluate dust emissions using Moderate Resolution Imaging Spectroradiometer (MODIS) and Infrared Atmospheric Sounding Interferometer (IASI) satellite observations of aerosol optical depth, respectively, in the visible and the thermal infrared over source areas. PM simulations were also evaluated compared to surface monitoring stations. Then, mineral dust emissions and their impacts on particle composition of several Chinese megacities were analyzed. Dust emissions and transport over China were simulated during three years (2011, 2013 and 2015). Annual dust contributions to the PM 10 budget over Beijing, Chengdu and Shanghai were evaluated respectively as 6.6%, 9.5% and 9.3%. Dust outbreaks largely contribute to poor air quality events during springtime. Indeed it was found that dust significantly contribute for 22%, 52% and 43% of spring PM 10 events (for Beijing, Chengdu and Shanghai respectively).
Highlights
Chinese atmospheric pollution is a major health problem with more than 82% of Chinese population living in environment exceeding particulate matter (PM2.5 ) concentrations of 75 μg m−3 [1](Chinese National Standard GB 3095-2012 for PM2.5 in an urban environment, 24H mean: 75 μg m−3 ; annual mean: 35 μg m−3 )
We first evaluated the accuracy of modeled dust emissions, using satellite Aerosol Optical Depth (AOD) observations over source regions, we evaluated the regional simulated PM concentration with in situ measurements
In our simulations [41,45] was used, about 15% of dust emissions were distributed into PM2.5, 61% were distributed into the coarse fraction of PM10 excluding PM2.5 (PM2.5 /PM10 = 0.20), 24% were distributed into a PM fraction with a diameter larger 10 μm, a fraction, which is not always considered [47]
Summary
Chinese atmospheric pollution is a major health problem with more than 82% of Chinese population living in environment exceeding particulate matter (PM2.5 ) concentrations of 75 μg m−3 [1]. Dust can be transported over large areas and impact cities PM load: a one-year study, based on 2000, from [19] resulted in an annual dust average in PM2.5 fraction of 13 μg m−3 in Beijing and 7 μg m−3 in Shanghai (corresponding to about 12% of PM2.5 load in both cities) It shows high seasonal variability, with higher values in spring. This induces different exposure to mineral dust pollution from sources mainly located in Western and Northern China (Cities location displayed later in the document) This choice is similar to cities selection made in previous work which reviewed observations of PM composition for representative Chinese megacities [22].
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