Microscopic comparison of aerosol particles collected at an urban site in North China and a coastal site in Japan

Highlights: • Aerosol particles were sampled at an urban site in China and a coastal site in Japan. • Microscopic properties of aerosol particles at two sites were analyzed by TEM. • Percentage of aerosol types and concentrations of air pollutants were compared. • Stronger photochemical oxidation of VOCs at coastal site led to thicker OM coating. -- Abstract: In order to understand the physicochemical properties of aerosol particles in Japan and China, transmission electron microscopy was used to analyze individual aerosol particles collected at two very different environmental sites, i.e., a continental site (T1) in North China and a coastal site (T2) in Japan in springtime. The average PM_2.5 concentration (52 μg/m³) at T1 was much higher than T2 (20 μg/m³) from 20 to 23 March 2014. Our study shows that sulfur-organic matter (S-OM) particles were the most abundant at both T1 and T2, and individual spherical primary organic matter (POM) particles were only observed at T1. More anthropogenic fly ash and metal particles were observed at T1, consistent with the heavier air pollution at T1 than T2, and the overall complexity of aerosol composition at T1 exceeded that at T2, due to the influence of regional industrial emissions. Further examination of S-OM particles suggest that S-OM coated particles accounted for 29.6% of total observed particles at T2 but only 8.6% at T1. However, the average thickness of OM coating was larger at T2 than at T1, indicating that the particles at T2 had aged longer than those at T1. These comparisons suggest that the OM coating thickness on sulfate depends on the transport distance of the air mass and on the concentration of atmospheric oxidants but should not be used to represent pollution levels. Compared with the coastal air in Japan, we know that urban aerosol particles in North China not only attain high concentrations but also have more complex aerosol components.