Study on the Pollution Characteristics and Sources of Ozone in Typical Loess Plateau City

Ground-level ozone is a secondary pollutant produced by photochemical reactions and it adversely affects plant and human health. Taiyuan City, a typical city on the loess plateau, is suffering from severe ozone pollution. We utilized the data from eight national environmental monitoring sites of Taiyuan, including concentrations of O(3)and nitric oxide, and meteorological factors, such as air temperature and wind, to study the pollution characteristics and sources of ozone (O-3) in Taiyuan in 2018. Results show that during 2018, the maximum value and 90th percentile of the maximum 8-h running average of O(3)concentration were 257 mu g/m(3)and 192 mu g/m(3), respectively. There were 72 days where the O(3)concentration exceeded the standard in 2018, which were mainly during April to August. The O(3)concentration increased from March, reached a high level in April through August, and decreased significantly from September. The O(3)concentrations displayed a typical "single peak" diurnal variation, which was high during the day with peak at around 13:00-15:00 and low at night. From April to August, the O(3)concentrations at Jinyuan was the highest, followed by Xiaodian and Taoyuan, and the O(3)concentrations at Shanglan and Nanzhai were the lowest. When the O(3)concentration exceeded the standard value, Jinyuan contributed the most to the O(3)pollution of Taiyuan, followed by Taoyuan and Xiaodian. High temperature and pressure, south and southwest winds can lead to an increase in O(3)concentration. The O(3)pollution in the Taiyuan urban area is caused by local generation, and the transportation of polluted air masses containing oxides of nitrogen (NOx) and volatile organic compounds (VOCs) emitted by industries, such as the coking and steel plants in counties of Jinzhong City in southern Taiyuan, and Qingxu County, and some counties in Lyuliang City to the southwest. In addition, the mountain winds and low nitric oxide concentration are the main reasons for the increase of O(3)concentration, often observed in Shanglan at night.