[Distribution Characteristics of Near Surface Ozone Volume Fraction in Shanxi Province Based on Atmospheric Composition Observation Network].

Based on the continuous data of O3， NO， NO2， and NOx and the meteorological data from March 2019 to February 2020 at six atmospheric composition observation stations in Shanxi Province， the characteristics and influence factors of O3 volume fractions were studied using statistical analysis and backward trajectory analysis. The results showed that O3 volume fractions were generally higher from April to September and lower from October to the following March. During the study period， O3 pollution represented by φ（MDA8O3）， i.e.， the maximum daily 8-h average of O3 volume fractions， was the most serious at the Jincheng and Linfen stations in the south of Shanxi， followed by that in the Wutaishan， Shuozhou， and Datong stations in the north， with the least pollution occurring at the Taiyuan station in the middle. There were differences between the urban and alpine stations， although their seasonal O3 volume fractions were both summer > spring > autumn > winter. O3 volume fractions at the urban station were usually lower than those at the alpine station； O3 at the urban station might have been influenced by photochemical reactions with precursor NOx； however， this was not the main source of high O3 at the alpine station. The peak and valley values appeared at 15：00 and 06：00， respectively， at the urban station， whereas they appeared at 20：00 and 10：00， respectively， at the alpine station， representing diametrically opposite diurnal variation patterns. Further， the daily amplitude of O3 at the urban station was much larger than that at the alpine station. For urban stations specifically， temperature was the most important meteorological factor affecting O3 volume fraction， compared with sunlight hours， precipitation， and total cloud cover. The NO2 volume fraction in the daytime affected the daily amplitude of O3； although the photochemical generation potential of O3 at the Taiyuan station was good， the O3 volume fractions were the lowest among urban stations due to strong NO titration. The higher O3 corresponded to lower NOx in which NO2 was dominant， and the higher NOx was largely composed of NO， under which conditions O3 would be depleted completely. The surface wind that affected O3 volume fractions of all stations primarily came from the southeast， south， and southwest， and specific wind speed led to the increase in O3 volume fraction. The geographical situation of the station would cause the difference in the transport of atmospheric pollutants， whereas the horizontal transmissions of high O3 from the North China Plain and Fenwei Plain were likely to be the common reason for the increase in O3 volume fraction in Shanxi.

[Influence of Pollutant Transport from Both Sides of the Taihang Mountains on Cross-Valley Urban Aerosols].

Based on hourly concentration data of PM10 and PM2.5 from 2017 to 2019 and wind speed and direction data at the corresponding times in Yangquan, an urban valley of the Taihang Mountains, the characteristics of air transport in a cross-valley urban area and their influence on aerosols in Yangquan were analyzed using the HYSPLIT model, cluster analysis, and the potential source contribution factor and concentration weight trajectory methods. The pollutant transport characteristics on the east and west sides of the Taihang Mountains were evaluated. The diurnal variation of the aerosols showed a single peak and single valley, with continuous improvements in aerosol concentration from evening to the morning of the next day. The maximum aerosol concentration occurs at 10:00-11:00 in winter and at 09:00 in other seasons, whereas the minimum value occurs at 15:00-16:00. The monthly mean aerosol concentration in Yangquan was highest in January and lowest in August, and PM10 was also high in March and April. The most frequent surface wind directions in Yangquan are easterly and westerly due to the topography of the cross valley. The average concentrations of aerosols were highest in the calm wind weather. Furthermore, the dust weather caused by the westerly wind in spring and autumn and the easterly transport in winter also causes an increase in aerosol concentration in Yangquan. The backward trajectories in combination with the pollution characteristics showed that 26.2% of the pollution trajectories are in spring, 36.4% are in autumn, and 33.7% are in winter, and that these are mainly distributed in the southwest and southeast of Yangquan and also in the northeast in winter. There was significant fine particle transport on both sides of the mountains, and the trajectories originating from or passing through the west side of the Taihang Mountains also transport coarse particles. As indicated by the pollution trajectory, the westerly air transport has an impact on PM10 in excess of the standard rate. The easterly transport has larger noise and mainly affects the exceedance rate of PM2.5. The main potential source areas of aerosol pollution in Yangquan differ in different seasons. The potential source areas are to the southwest and southeast of Yangquan in spring, the southwest and south of Yangquan in autumn, and the south and east of Yangquan in winter. The areas with high PSCF and CWT in PM2.5 were in the southeast region, but those for PM10 were in the southwest region. The area southeast of Shanxi and the border area north of Henan are the main source areas. Based on the influence of aerosol pollution transmission in Yangquan, the cross-valley urban area is affected simultaneously by the areas east and west of the Taihang Mountains, especially by PM2.5 transport from east to west.