Abstract
PM2.5 was sampled from January 2017 to May 2018 at an urban, suburban, industrial, and rural sites in Xining. The annual mean of PM2.5 was highest at the urban site and lowest at the rural site, with an average of 51.5 ± 48.9 and 26.4 ± 17.8 μg·m−3, respectively. The average PM2.5 concentration of the industrial and suburban sites was 42.8 ± 27.4 and 37.2 ± 23.7 μg·m−3, respectively. All sites except for the rural had concentrations above the ambient air quality standards of China (GB3095-2012). The highest concentration of PM2.5 at all sites was observed in winter, followed by spring, autumn, and summer. The concentration of major constituents showed statistically significant seasonal and spatial variation. The highest concentrations of organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and water-soluble inorganic ions (WSIIs) were found at the urban site in winter. The average concentration of F− was higher than that in many studies, especially at the industrial site where the annual average concentration of F− was 1.5 ± 1.7 μg·m−3. The range of sulfur oxidation ratio (SOR) was 0.1–0.18 and nitrogen oxidation ratio (NOR) was 0.02–0.1 in Xining. The higher SO42−/NO3− indicates that coal combustion has greater impact than vehicle emissions. The results of the potential source contribution function (PSCF) suggest that air mass from middle- and large-scale transport from the western areas of Xining have contributed to the higher level of PM2.5. On the basis of the positive matrix factorization (PMF) model, it was found that aerosols from salt lakes and dust were the main sources of PM2.5 in Xining, accounting for 26.3% of aerosol total mass. During the sandstorms, the concentration of PM2.5 increased sharply, and the concentrations of Na+, Ca2+ and Mg2+ were 1.13–2.70, 1.68–4.41, and 1.15–5.12 times higher, respectively, than annual average concentration, implying that aerosols were mainly from dust and the largest saltwater lake, Qinghai Lake, and many other salt lakes in the province of Qinghai. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was utilized to study the surface components of PM2.5 and F− was found to be increasingly distributed from the surface to inside the particles. We determined that the extremely high PM2.5 concentration appears to be due to an episode of heavy pollution resulting from the combination of sandstorms and the burning of fireworks.
Highlights
Due to rapid urbanization, industrialization, and economic growth in China, many cities experience frequent hazeAtmosphere 2020, 11, 953; doi:10.3390/atmos11090953 www.mdpi.com/journal/atmosphereAtmosphere 2020, 11, 953 pollution that profoundly impacts visibility, the global climate, and human health [1,2,3,4,5]
In the past few decades, most studies have focused on PM2.5 and the relevant haze pollution in developed areas of China such as the Jin-Jing-Ji, Pearl River Delta, and Yangtze River Delta areas [17,18,19,20]
Many publications have reported on the haze pollution of western cities such as Xi’an in China, but few have reported on PM2.5 in the Qinghai–Tibet Plateau
Summary
Industrialization, and economic growth in China, many cities (especially in some developed or industrial areas like northern and eastern China) experience frequent hazeAtmosphere 2020, 11, 953; doi:10.3390/atmos11090953 www.mdpi.com/journal/atmosphereAtmosphere 2020, 11, 953 pollution that profoundly impacts visibility, the global climate, and human health [1,2,3,4,5]. The chemical composition of PM2.5 is complex, and includes water-soluble inorganic ions (WSIIs), carbonaceous compositions, and mineral components that have significant influence on the physical and chemical properties of aerosols [8,9,10,11]. The amount and chemical properties of water-soluble organic carbon (WSOC) can affect the hygroscopic growth and cloud condensation nucleus activity of aerosols [12]. The formation mechanism of secondary compositions is highly dependent on the concentration of precursor pollutants, the oxidative state of the atmosphere, and meteorological conditions [16]. Many publications have reported on the haze pollution of western cities such as Xi’an in China, but few have reported on PM2.5 in the Qinghai–Tibet Plateau
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