Atmospheric hydrogen peroxide (H₂O₂) at the foot and summit of Mt. Tai : variations, sources and sinks, and implications for ozone formation chemistry

Abstract

Hydrogen peroxide (H2O2) acts as a terminal sink for atmospheric HOx radicals (OH and HO2), playing a key role in tropospheric O3 formation. However, there are few field measurements of atmospheric H2O2 to assess its role in O3 formation, especially for the seriously polluted region of the North China Plain. In this study, H2O2 concentrations were measured at the foot of Mt. Tai from May to July 2018 and the summit of Mt. Tai from May to June 2019, with average values of 0.93 ± 1.01 and 2.05 ± 1.20 ppb, respectively. H2O2 exhibited a pronounced diurnal variation with a noon-peak at the foot of Mt. Tai, which could be well reproduced by a gas-phase box model with H2O2 dry deposition velocity of 3 cm s−1 included, indicating H2O2 was mainly photochemically produced. Modeling analysis showed H2O2 production at the foot was most sensitive to alkenes and aromatics, while the source and sink for H2O2 were dominated by HO2 recombination and dry deposition, respectively. Compared with the summer-measurement in 2007, the remarkable elevation of H2O2 at the summit might be ascribed to volatile organic compounds (VOCs) increase and SO2 decline. Both H2O2-O3 correlation and H2O2/NOz ratio suggested O3 formation at the foot of Mt. Tai was mainly VOC-sensitive in the early morning and shifted to NOx-sensitive thereafter. Therefore, reduction of VOCs emission especially for the reactive species of alkenes and aromatics in the morning as well as NOx emission around noontime will be effective for mitigating the serious O3 (as well as H2O2) pollution in Tai'an city.