Perchlorate in Year-Round Antarctic Precipitation

Year-round precipitation in coastal East Antarctica and Antarctic Peninsula was used to investigate the seasonal patterns in sources of atmospheric perchlorate (ClO4- ${{\text{ClO}}_{4}}<^>{-}$). Although featuring distinct climates, the two locations exhibit similar annual mean and seasonal cycles of ClO4- ${{\text{ClO}}_{4}}<^>{-}$ concentration, with higher values in autumn and lower concentrations in winter and spring. Tropospheric formation dominates atmospheric ClO4- ${{\text{ClO}}_{4}}<^>{-}$ in spring and summer, which is influenced by both oxidants levels and environmental conditions (e.g., air humidity). Tropospheric ClO4- ${{\text{ClO}}_{4}}<^>{-}$ production may also be promoted by elevated levels of oxidants brought by air mass from the interior Antarctic ice sheet in spring and summer. The autumn concentration maximum may originate from ClO4- ${{\text{ClO}}_{4}}<^>{-}$ produced in the stratosphere through reactions between reactive chlorine and ozone during spring and summer. In winter, the stratospheric input may contribute to ClO4- ${{\text{ClO}}_{4}}<^>{-}$ via polar stratospheric clouds sedimentation. Perchlorate (ClO4- ${{\text{ClO}}_{4}}<^>{-}$) is an inorganic anion with a persistent presence in the environment, where its exposure can pose a significant health risk to humans. Environmental ClO4- ${{\text{ClO}}_{4}}<^>{-}$ is derived from both man-made and natural sources. Natural ClO4- ${{\text{ClO}}_{4}}<^>{-}$, widespread in the environment, is thought to be formed in the atmosphere. However, knowledge on the sources and, in particular, the formation mechanisms of natural ClO4- ${{\text{ClO}}_{4}}<^>{-}$ is quite limited. Antarctica, with negligible man-made sources, is one of the best regions for investigations on natural ClO4- ${{\text{ClO}}_{4}}<^>{-}$. Year-round precipitation samples were collected at China Zhongshan Station located in coastal East Antarctica and China Great Wall Station on King George Island, Antarctic Peninsula. Results show that atmospheric ClO4- ${{\text{ClO}}_{4}}<^>{-}$ concentration presents obvious seasonal cycles, which are related to variations in sources. A significant amount of ClO4- ${{\text{ClO}}_{4}}<^>{-}$ is associated with tropospheric chemistry in spring and summer. Precursor levels, environmental conditions, and air mass from the interior Antarctica may influence tropospheric ClO4- ${{\text{ClO}}_{4}}<^>{-}$ formation. The maximum concentration in autumn may originate from ClO4- ${{\text{ClO}}_{4}}<^>{-}$ formed in the stratosphere during spring and summer, and the stratospheric input may also contribute to atmospheric ClO4- ${{\text{ClO}}_{4}}<^>{-}$ in winter. Antarctic atmospheric perchlorate (ClO4- ${{\text{ClO}}_{4}}<^>{-}$) concentration at different locations exhibits a clear seasonal cycleThe highest concentration in autumn is likely related to ClO4- ${{\text{ClO}}_{4}}<^>{-}$ produced in the stratosphere in spring and summerMajor source of ClO4- ${{\text{ClO}}_{4}}<^>{-}$ in spring and summer is tropospheric formation influenced by both oxidants and environmental conditions