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 O₃ and nitric oxide, and meteorological factors, such as air temperature and wind, to study the pollution characteristics and sources of ozone (O₃) in Taiyuan in 2018. Results show that during 2018, the maximum value and 90th percentile of the maximum 8-h running average of O₃ concentration were 257 μg/m³ and 192 μg/m³, respectively. There were 72 days where the O₃ concentration exceeded the standard in 2018, which were mainly during April to August. The O₃ concentration increased from March, reached a high level in April through August, and decreased significantly from September. The O₃ 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 O₃ concentrations at Jinyuan was the highest, followed by Xiaodian and Taoyuan, and the O₃ concentrations at Shanglan and Nanzhai were the lowest. When the O₃ concentration exceeded the standard value, Jinyuan contributed the most to the O₃ pollution of Taiyuan, followed by Taoyuan and Xiaodian. High temperature and pressure, south and southwest winds can lead to an increase in O₃ concentration. The O₃ 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 O₃ concentration, often observed in Shanglan at night.

Atmospheric peroxides, especially hydrogen peroxide (H₂O₂), are essential oxidants. The peroxide concentration is closely related to the extent of OH radicals and the O₃ cycle in the tropospheric atmospheric chemistry. However, only a few studies have investigated their atmospheric concentrations in China because of inadequacies in the measurement techniques or higher costs of analytical instruments. Therefore, it is essential to design a suitable analysis method of peroxides with higher sensitivity, lower detection limit, and low cost. In view of that, this study investigated the optimum analysis conditions of two H₂O₂ analytical techniques: the high-performance liquid chromatography (HPLC) with fluorescence detection using two-enzyme catalysis of horseradishperoxidase (HRP method) and Hemin (Hemin method). Furthermore, these two analysis methods were systematically compared in terms of detection limit, calibration curve, precision, accuracy, and applicability for the first time. The findings showed that the HRP method had a lower detection limit, higher sensitivity, and better applicability for detecting H₂O₂ and methyl hydroperoxide (MHP) than the Hemin method. Moreover, the HRP method is better suitable for H₂O₂ and MHP detection, which requires low detection limits and high sensitivity. Besides this, the Hemin method is inexpensive and is more suitable for detecting hydroxyl alkyl peroxides (C ≥ 3). The atmospheric concentrations (average) of H₂O₂ and MHP were 0.60 ± 0.37 ppb and 0.081 ± 0.039 ppb, respectively, as determined by the HRP method. Importantly, atmospheric peroxide concentrations were higher on sunny days than on cloudy days in Beijing in September 2016. H₂O₂ concentrations showed a diurnal variation with the lowest value in the morning and two peaks at 13:00–17:00. In contrast, MHP concentrations were lowest in the morning and highest after 17:00. Photochemical reactions were responsible for the production of H₂O₂ and MHP. The reactions of O₃ and olefins emitted by motor vehicles also caused H₂O₂ concentration to increase during the evening rush hour.