Chemical Composition Characteristics and Source Contributions of Precipitation in Typical Cities on the North Slope of Tianshan Mountain in Xinjiang during 2010–2019

Air pollution in heavy industrial cities along the northern slope of the Tianshan Mountains, Xinjiang: characteristics, meteorological influence, and sources

The spatiotemporal characteristics, relationship with meteorological factors, and source distribution of air pollutants (January 2017-December 2021) were analyzed to better understand the air pollutants on the northern slope of the Tianshan Mountains (NSTM) in Xinjiang, a heavily polluted urban agglomeration of heavy industries. The results showed that the annual mean concentrations of SO₂, NO₂, CO, O₃, PM_2.5, and PM₁₀ were 8.61-13.76 μg m^-3, 26.53-36.06 μg m^-3, 0.79-1.31 mg m^-3, 82.24-87.62 μg m^-3, 37.98-51.10 μg m^-3, and 84.15-97.47 μg m^-3. The concentrations of air pollutants (except O₃) showed a decreasing trend. The highest concentrations were in winter, and in Wujiaqu, Shihezi, Changji, Urumqi, and Turpan, the concentrations of particulate matter exceeded the NAAQS Grade II during winter. The west wind and the spread of local pollutants both substantially impacted the high concentrations. According to the analysis of the backward trajectory in winter, the air masses were mainly from eastern Kazakhstan and local emission sources, and PM₁₀ in the airflow had a more significant impact on Turpan; the rest of the cities were more affected by PM_2.5. Potential sources included Urumqi-Changj-Shihezi, Turpan, the northern Bayingol Mongolian Autonomous Prefecture, and eastern Kazakhstan. Consequently, the emphasis on improving air quality should be on reducing local emissions, strengthening regional cooperation, and researching transboundary transport of air pollutants.

Impact of COVID-19 restrictions on air quality and surface urban heat island effect within the main urban area of Urumqi, China

The outbreak of coronavirus in 2019 (COVID-19) posed a serious global threat. However, the reduction in man-made pollutants during COVID-19 restrictions did improve the ecological environment of cities. Using multi-source remote sensing data, this study explored the spatiotemporal variations in air pollutant concentrations during the epidemic prevention and control period in Urumqi and quantitatively analyzed the impact of different air pollutants on the surface urban heat island intensity (SUHII) within the study area. Urumqi, located in the hinterland of the Eurasian continent, northwest of China, in the central and northern part of Xinjiang was selected as the study area. The results showed that during COVID-19 restrictions, concentrations of air pollutants decreased in the main urban area of Urumqi, and air quality improved. The most evident decrease in NO2 concentration, by 77 ± 1.05% and 15 ± 0.98%, occurred in the middle of the first (January 25 to March 20, 2020) and second (July 21 to September 1, 2020) COVID-19 restriction periods, respectively, compared with the corresponding period in 2019. Air pollutant concentrations and the SUHIIs were significantly and positively correlated, and NO2 exhibited the strongest correlation with the SUHIIs. We revealed that variations in the air quality characteristics and thermal environment were observed in the study area during the COVID-19 restrictions, and their quantitative relationship provides a theoretical basis and reference value for improving the air and ecological environment quality within the study area.

Chemical Compositions of Rainfall Water in Nyingchi City, Tibet

Understanding precipitation chemistry is highlighted as important worldwide due to its close relationship with air quality and impacts on ecosystems. However, the chemical composition of precipitation is limited in Tibet, where alpine ecosystems are sensitive to global change. Here, rainwater samples were collected in Nyingchi city from January 2021 to December 2021, and a total of 44 samples were obtained. Major ions (NO3−, NH4+, Cl−, SO42−, Na+, K+, Ca2+ and Mg2+) were analyzed. Results showed that the predominant ions in the precipitation were Ca2+, Na+, SO42−, and Cl−. Precipitation was mainly concentrated in summer, accounting for 65.2% of all samples collected during the monitoring period. As a result, ion deposition fluxes were mainly concentrated in summer, accounting for 55%, 53%, 84%, 82%, 61%, 63%, 75.8%, and 37.8% of the annual Ca2+, K+, Mg2+, Na+, NH4+, Cl−, SO42−, and NO3−, respectively. Backward trajectory analysis revealed that airmasses were mainly from the southern direction, but the sources varied widely. In addition, Na+ and Cl− ions were dominated by the sea source fraction; the ions of Ca2+ and K+ were dominated by crustal fraction sources. The NH4+ and NO3− ions were mainly influenced by local pollution. However, SO42− was mainly from long distance transports. Our results suggest that ions abundance was varied largely in different direction airmasses in southeast Tibet. Considering that ion deposition fluxes were mainly concentrated in the summer and the airmasses were mainly from the southern direction in this season, the pollutants from the southern direction the environmental effects of those ions should be given more attention in the future.