Hydrogen peroxide(H₂O₂) acts as a reservoir for HOx radicals in the atmosphere and is closely related to the O₃ formation. In aqueous phase, it serves as a significant oxidant for the formation of SO42-. This study was conducted at Korea University during the SIJAQ campaign in May and June 2022, with measurements of H₂O₂, other reactive gases and particulate matters. In 2021, H₂O₂ was measured for within one week per each month from July to September.
During the measurement periods of May and June 2022, the average H₂O₂ mixing ratio was 0.66 ± 0.39 ppbv. The highest concentration of H₂O₂, observed at 2.33 ppbv, occurred at the end of July with elevated levels of O₃ (>100 ppbv) and PM2.5 (>50 ㎍ m-3). During the SIJAQ campaign in 2022, H₂O₂ mixing ratio showed the maximum of 2.03 ppbv in late May and remained around 1 ppbv during nighttime.
During the measurement period, H₂O₂ maintained high until late evening after an increase in daytime O₃, and the linear relationship between H₂O₂ and O₃ was not clear. In May and June 2022, TVOC and NOx showed a good correlation, while TVOC and NOz were clearly distinguishable on a daily in 2022. Particularly in 2022, O₃ and PM2.5 showed a strong correlation and were increased together (R²=0.22).
Based on previous studies, May and June in 2022 was categorized by three synoptic meteorological patterns (P1~P3). Unlike 2016, there were no stagnation, persistent anticyclone for more than five days, in 2022, and the Transport regime was dominant from May 17th to 29th, 2022. TVOC and NOx levels were high in P1 periods. Under high NOx level, O₃ concentrations were low during the night, and H₂O₂ formation was suppressed during the daytime, resulting in lower levels of O₃ and H₂O₂. On the other hand, in the P2 and P3, which represented aged air masses, NOz, O₃, and PM2.5 were high. In the aged air, H₂O₂ and O₃ levels increased in transport airmass, while in stagnant airmass, it was consumed by the formation of particulate sulfate in aqueous phase, leading to lower H₂O₂ levels.
In summer, including May and June, H₂O₂ showed different distribution under distinct photochemical airmass, playing an important role as an oxidant in both the gas and aqueous phases. As a policy, when diagnosing O₃ formation, H₂O₂ can indicate O₃ formation on TVOC-NOx sensitivity in fresh airmass. However, in aged airmass, the influences of transport and aerosol must be considered. By investigating the behavior of H₂O₂, it can provide insights into the complex interactions in atmospheric chemistry, contributing to a better understanding of air quality and its implications.