Parameterized atmospheric oxidation capacity during summer at an urban site in Taiyuan and implications for O3 pollution control

In recent years, summer ozone pollution shows a significant upward trend in many cities of China, affecting human health and ecosystems. The atmospheric oxidation capacity (AOC) is the core driving force for converting primary pollutants into secondary pollutants. In order to better understand the characteristics of AOC in summer, the comprehensive observation of VOCs (including OVOCs) was conducted at an urban site in Taiyuan from July 20 to August 3, 2020. The parameterized analysis of AOC and ROH was carried out by combining with the simulated photolysis rates (JO1D, JNO2 and JNO3). The results showed that the mean value of MDA8 O3, AOC and ROH were 84.2 ppbv, 2.4 × 107 molecules cm-3 s-1 and 28.3 s-1, respectively. The major reductants of AOC were CO (37.6%), isoprene (21.7%) and formaldehyde (16.8%). Diurnal variations of AOC showed a peak at noon, the major oxidants for AOC were OH (97.7%) and O3 (78.7%) during the daytime and nighttime, respectively. The mean value of MDA8 O3, AOC and VOCs-AOC during the pollution period (MDA8 O3 > 75 ppbv) were 33.0%, 45.0% and 59.3% higher than the non-pollution period, respectively. The OH reactivity ratio of NOx and VOCs indicated that O3 formation occurred under a VOC-limited regime. The backward trajectory analysis showed that VOCs from southwestern airmass had the highest AOC (2.0 × 107 molecules cm-3 s-1), and the domain contributors were isoprene (39.0%), formaldehyde (24.9%), acetaldehyde (9.8%) and ethylene (4.4%). This study could provide some references for regulating AOC to alleviate O3 pollution.