Abstract:
There are large gaps in the domestic and international research on the characteristics of ozone (O
3) concentration evolution in desert areas. Alxa Left Banner is a typical desert city in western China; it has high background O
3 concentrations because of the low intensity of anthropogenic activities. From 2015 to 2022, the annual growth of daily maximum 8-h average ozone (MDA8 O
3) was approximately 2 μg m
−3. The average MDA8 O
3 values in spring, summer, autumn, and winter were 111.3 μg m
−3, 132.3 μg m
−3, 101.8 μg m
−3, and 82.9 μg m
−3, respectively. The existence of favorable conditions, namely, high temperature and strong radiation, promotes the atmospheric photochemical reaction of O
3 and enhances the secondary production of O
3; therefore, O
3 pollution incidents mainly occur in the summer. The O
3 concentrations in Alashan Left Banner were 93–106 μg m
−3 on summer nights under the influence of the NO titration effect, indicating that this region featured a high background O
3 level. The greater the distance from the observation point to the ground, the higher the O
3 concentration. The observations showed that the near-surface anthropogenic emissions have a direct and significant influence on the vertical O
3 concentrations at three stations (Huanbaojuxinlou, Mengeryou, and Xihuayuan stations) with different heights over the ground surface. The O
3 concentration at Huanbaojuxinlou station (22 m above the ground) was set as a criterion. The O
3 concentration at Mengeryou station, 15 m above the ground, was lower by 5–25 μg m
−3 during the night and higher by 5 μg m
−3 at noon. The O
3 concentration at Xihuayuan station, 12 m above the ground, was lower by 10–25 μg m
−3 during the night and higher by 5 μg m
−3 at noon. A strong NO titration effect was observed in the near-ground atmosphere in the urban areas at night. However, high O
3 concentrations were observed in the near-ground atmosphere because of convective diffusion and rapid photochemical reactions. Thus, the weak effect of human activities on O
3 concentration was illustrated, and the vertical distribution characteristics of O
3 in desert cities were captured.
下载: