Abstract:
There are large gaps in domestic and international research on the characteristics of ozone(O3) concentration evolution in desert areas. Alxa Left Banner belongs to a typical desert city in the western China, which has high background concentrations of O3 on the basis of low intensity of anthropogenic activities. From 2015 to 2022, the annual growth of the 8-hour moving average of daily maximum ozone (MDA8 O3) was about 2 μg·m-3. And the average MDA8 O3 in spring, summer, autumn and winter was 111.3 μg·m-3, 132.3 μg·m-3, 101.8 μg·m-3 and 82.9 μg·m-3. Due to the favourable conditions of high temperature and strong radiation, the atmospheric photochemical reaction of O3 will be promoted and the secondary production of O3 will be enhanced, thus the O3 pollution incidents mainly appear in the summer. The O3 concentrations in Alashan Left Banner were 93-106 μg·m-3 in the summer night under the influence of NO titration effect, indicating that the Alashan region was controlled by high background O3 level. The higher the distance from the observation site to the ground, the higher the O3 concentration. The observations show that the near-surface anthropogenic emissions has direct and significant influence on the vertical O3 concentrations at three stations with different heights over the ground surface. Setting the O3 concentration at the Huanbaojuxinlou Station (22 m above the ground) as a criteria. The O3 concentration at the Mengeryou Station, which is 15 m above the ground, is lower by 5-25 μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon; the O3 concentration at the Xihuayuan Station, which is 12 m above ground, is lower by 10-25μg·m-3 during the night, and it is higher by 5 μg·m-3 during the noon. The stronger NO titration effect was found in the near ground atmosphere in the urban area at night. However, the higher O3 was found in the near ground atmosphere due to the convective diffusion and rapid photochemical reaction. The effect of weak human activities on O3 concentration was illustrated, and the vertical distribution characteristics of O3 in desert cities were reflected.