Exploring The Characteristics And Causes Of Ozone Pollution Around Traffic Arteries

In the context of China’s rapid economic development,the standard of living of residents has increased significantly,and the number of motor vehicles powered by internal combustion engines has been rising,the concentration of nitrogen oxides and volatile organic compounds（VOCs）emitted from vehicle exhaust has increased year by year,and the concentration of ozone（O₃）produced by the photochemical reaction of vehicle exhaust has also increased.Therefore,the annual average concentration of O₃is increasing year by year,which has attracted the attention of people from all walks of life.Current research on O₃pollution includes two aspects:the causes and human hazards of O₃at the microscopic level,and the spatial and temporal distribution and macroscopic effects at the large scale.There has been relatively little discussion of studies at small and medium scales,such as the areas around traffic arteries.In order to understand the characteristics of O₃concentration changes in the area around the traffic arteries and to investigate the causes of near-surface O₃pollution,this study is based on air pollution monitoring stations,meteorological monitoring stations and traffic flow long time series data of two roadside stations（Yangji Station and Huangsha Station）in Guangzhou from January to June 2021,and by comparing with the background station（Luhu Station）.The characteristics of O₃,NO₂and PM_2.5concentrations at different time scales at roadside and background stations in Guangzhou were analyzed using a characteristic analysis model.The priority of the influencing factors of O₃concentration change was studied by contribution analysis,and the main causes of O₃concentration change around the traffic arteries in Guangzhou were explored by using correlation analysis model.The main research contents and results of this paper are as follows.（1）It was found that the typical pollution day time scales at the three stations showed different variation characteristics.The daily variation of O₃concentration is"single-peak",with the peak occurring at 16-18 hours,and the difference between cold and warm seasons is small;the valley of NO₂concentration at the roadside station occurs at 4 and 16 hours,and the background station occurs at 16 hours,and the O₃concentration is larger in the cold season;the O₃concentration is larger in the cold season;the overall daily variation of PM_2.5concentration is flat,and the cold season concentration is larger than the warm season due to the influence of traffic emission and the weakening of nighttime diffusion in winter.（2）Based on the qualitative and quantitative data,this paper investigates the variation patterns of O₃and its precursor NO₂concentrations at three sites by statistical analysis,comparative analysis and visualization analysis,and concludes that there is a significant weekend effect on O₃concentrations due to differences in human activities,meteorological conditions and emission sources,i.e.,O₃concentrations are significantly higher at weekends than at weekdays,and O₃concentrations are higher at Luhu Station among the three stations;NO₂concentrations are higher at weekdays,with the lowest concentrations at Luhu Station and the highest concentrations at Huangsha Station.Huangsha station has the highest concentration.（3）The relationship between O₃pollution and influencing factors such as precursors,meteorology and dynamic traffic parameters was investigated based on qualitative and quantitative studies.Traffic and meteorological parameters（temperature,solar radiation,RH and precipitation）were significantly correlated with O₃concentrations at the two roadside stations.The results indicate that traffic emissions contribute to,but are not determinant of,urban O₃pollution and that meteorological factors also influence O₃concentrations.（4）A two-week case study was conducted to quantify the effect of solar radiation on O₃concentrations in Guangzhou.O₃concentrations exceeded 90μg/m³at all three sites on sunny days,which were 2～3 times higher than those on cloudy days due to meteorological conditions.Dynamic traffic conditions（travel time ratio）were less correlated with O₃and NO₂concentrations at the two roadside stations.