Abstract：To understand the physiochemical characteristics of individual aerosol particles in Sichuan Basin, samples of atmospheric individual aerosol particles were collected in a typical city (Chengdu) and a background area (Mt. Emei) in Sichuan Basin. Then the chemical composition, morphology and mixing state of 3923 aerosol particles in the two regions were observed and analyzed by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDS). The results showed that the individual aerosol particles in the two regions mainly included organic matter, S-rich, mineral, soot and fly ash/metal particles. In addition to a small amount of external mixing, most particles existed in the form of internal mixing, i.e., two or more particles mixed with each other. Through the comparative of the characteristics of aerosol particles in different pollution conditions in Chengdu, it can be found that the proportion of the internal mixing particles in the "polluted days" (74.2%) was higher than that of "clean days" (68.6%). Moreover, compared with "clean days", the particles size distribution range of "pollution days" was wider and the peak range was larger, indicating that the mixing of particles tends to be stronger with the aggravation of pollution. The comparison between Chengdu and Mt. Emei showed that the OM-S particles dominated the particles in Chengdu (accounted for 50.2%), while the particles in Mt. Emei were dominated by OM particles (accounted for 50.5%). Meanwhile, the contribution of sulfur-containing particles (such as OM-S) in Chengdu was higher than that of Mt. Emei, while the proportion of two carbon-containing particles (such as soot and OM-soot) in Mt. Emei was higher than that of Chengdu. In addition, the range of particle size distribution and peak range between Chengdu and Mt. Emei were different, which highlighted the differences of the sources and aging mixture of particles between the two regions. In Mt. Emei, the proportion of soluble particles (such as sulfur-containing particles) in rainfall day significantly decreased compared with that of non-rainfall day, while the proportion of particles with small particle size and strong hydrophobicity (such as soot and OM-soot particles) increased correspondingly.
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