Investigating the Atmospheric Production of Perchlorate: Inference from Polar Ice Cores

• Main Author: Cox, Thomas S.
• Format: Text
• Language: English
• Published: Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange 2017
• Subjects: atmospheric production; ice core; ozone; Perchlorate; post-depositional loss; stratospheric chlorine; Analytical Chemistry; Atmospheric Sciences; Environmental Sciences; Antarctic; Antarc*
• Online Access: https://openprairie.sdstate.edu/etd/1664; https://openprairie.sdstate.edu/context/etd/article/2690/viewcontent/Cox_Thomas_2017.pdf

Perchlorate (ClO4) in the environment is of concern, because of potential health risks to humans, among other reasons. Evidence suggests that the majority of environmental perchlorate is formed in the atmosphere (likely in the stratosphere), in chemical processes involving ozone and stratospheric chlorine. A lack of knowledge in regards to the processes has resulted in a limited understanding of the environmental conditions and variables that influence perchlorate production and consequently perchlorate prevalence and variability in the environment. In this study, perchlorate was measured, using an established ion chromatography-­‐electrospray ionization-­‐tandem mass spectrometry (IC-­‐ESI-­‐ MS/MS) technique, in over 1,600 snowpit and ice core samples collected at several Antarctic locations. Several ice core records were developed covering the 20th century; however, interpretation of the records is complicated by depositional and post-­‐depositional processes that affect perchlorate concentrations in snow. It appears that wet deposition is significant at sites where accumulation is high and dry deposition is significant where accumulation is low; additionally, perchlorate concentration in snow may undergo significant changes (~50% decrease) at low accumulation sites. Yet, the records suggest that perchlorate is produced from activated chlorine species (chlorine free radicals) in the stratosphere and that increases in stratospheric chlorine -­‐ due to anthropogenic emissions of chlorine compounds (CFCs) -­‐ are likely driving the increasing trend of perchlorate production. Furthermore, perchlorate variability appears to also be indirectly influenced by stratospheric temperature and stratospheric sulfate aerosols.