| Other Abstract | In this paper, the characteristics, causes and influencing factors of ozone pollution in Lanzhou are researched. Based on the measurements of ozone and its precursors on several sites of geographical difference in Lanzhou from 2013 to 2018, the annual variation of ozone pollution in Lanzhou in recent years were analyzed, and then a more detailed study was carried out. I compare the ozone concentration and diurnal variation of downtown city with industrial areas in different seasons, as well as the transitional zone between them.I study the different characteristic of ozone pollution in suburb and in city. I also study the transport of ozone and its precursors by compare the ozone concentration and diurnal variation in days prevailing easterly with days not prevailing easterly. By means of arithmetic statistic mean method, calculating backward trajectory of airflow and clustering into four groups, using surface atmospheric chemical observation data, satellite remote sensing data and reanalysis data, the effects of meteorological conditions, chemical processes and vertical transportation on the spatial and temporal distribution of ozone in summer which ozone pollution is the most serious were comprehensively analyzed,and two fundamental influencing factors of ozone pollution in Lanzhou were found. On this basis, typical cases were selected to study how the fundamental factors affect ozone pollution in Lanzhou,explain how the precursor concentration or weather dynamics and conditions affect ozone pollution.The following conclusions are drawn :1)The ozone pollution in Lanzhou is aggravating. The ozone pollution is the most serious in summer and the lightest in winter. 2)The number of cars in Lanzhou is lower than Hangzhou, Changsha, Shanghai and other cities, but the annual average hourly concentration of O3 or NO2 is higher than these cities. 3)Due to the influence of solar radiation, the diurnal variation of ozone in urban stations presents a single peak pattern in each season. 4)The zone where lots of factories located in the industrial area is the most serious ozone pollution areas in Lanzhou,has an important impact on the other areas in Lanzhou through transmit and discharge pollutant. Influenced by regional precursor concentration, precursor and ozone transport, the concentration of ozone and total oxide in industrial and transitional zone near the factories rises faster than that in the downtown city in daytime, the peak concentration is larger than that in the downtown area and appears earlier, which is more affected by wind than that in the downtown area, while the downtown area are less affected by factories because distance is far,the O3 and OX peak concentration are low and appear late. 5)Ozone concentration in suburban area is significantly higher at night than that in urban area due to the low NO concentration in suburban area.Meanwhile, the diurnal variation of ozone concentration is smaller in suburban area.The total oxide concentration in suburban area is not much different from that in urban area at night, and is lower than that in urban area during daytime. 6)In summer, the backward trajectory in Lanzhou can be divided into four representative paths, one of which is from the northwest of Gansu Province,which the median peak ozone concentration is the highest.What the path is short indicates that the weather condition is relatively stable and the phenomenon of high temperature and low humidity is easy to occur. Under the influence of this kind of air mass, the average concentration of CO and NO2 in Lanzhou is higher, the 2 m temperature away from the ground is higher, and the boundary layer is also higher, so this kind of mass is greatly influenced by photochemistry formation and STE. 7)If there is strong solar radiation and the atmosphere is rich in ozone precursors , strong photochemical reactions will occur, leading to ozone pollution. 8)Tropopause folding can cause STE process, which leads to the downward transport of stratospheric high concentration ozone to the troposphere. The potential vorticity in the upper troposphere and the lower stratosphere increases significantly, the humidity is low and the ozone concentration is high in troposphere. When tropopause folding occurs, the upper-level jet and pressure trough associated with Frontogenesis and cyclone can be observed at high altitude. 9)Thermal effects, which is caused indirectly by strong solar radiation, will cause the rise of the top of the boundary layer and tropopause, leading to STE which makes the potential vorticity increasing in the upper and middle troposphere. In the process of STE, stratospheric high concentration ozone is transported downward to the troposphere. |
