Study on Spatiotemporal Changes and Related Factors of Near-Surface Atmospheric Composition in Lhasa City

Lhasa City is located in the hinterland of the Qinghai–Tibet Plateau. The problem of ozone (O₃) pollution has become significant in recent years. Based on the monitoring data of O₃, NO, NO₂, NO_x, CO, SO₂, PM2.5, and PM10 from six monitoring stations in the Lhasa urban area from 2013 to 2018, this paper uses statistical methods to study various pollutants in Lhasa. This especially includes the temporal and spatial distribution characteristics of O₃, the relationship between ozone and its precursors, and the influence of meteorological conditions on ozone.The results show that (1) O₃ concentration in the Lhasa urban area has been increasing in recent years. Further, O₃ replaces PM10 as the primary pollutant in the Lhasa urban area. Additionally, the annual days of excess O₃ have reached 55 d, accounting for 49.4% of the total days. (2) The O₃ concentration has increased significantly after 2016, with an increasing rate of 16.34 μg m^-3 a^-1 from 2016 to 2018, and the O₃ concentration is the highest in 2018 (91.48 μg/m³). The annual difference in the ozone concentration shows that the annual O₃ concentration has gradually increased since 2015. (3) The O₃ concentration increases in spring and decreases in winter; furthermore, the urban area has a higher O₃ concentration than the suburban area, and it is negatively correlated with the concentration of NO, NO₂, and NO_x (−0.6). Therefore, it is possible that ozone generation is inhibited by NO_x. (4) O₃ correlates well with air temperature; therefore, with an increase in precipitation and humidity, the O₃ concentration is inhibited. Furthermore, the O₃ concentration is greatly affected by the season and wind direction and speed. These factors can be related to the characteristics of long-distance transport and the impact of human activities (stationary sources) on the plateauing ecological environment.