Design and Atmospheric Application of a Large-Volume UV-Irradiated FEP Chamber for Mercury Redox Chemistry Studies

Abstract Understanding the atmospheric redox chemistry of mercury (Hg) is critical for accurately predicting its global transport, deposition, and environmental impacts. However, large uncertainties remain with respect to reaction mechanisms and oxidation rates that convert elemental mercury (Hg0) to its oxidized forms (HgI, HgII). In this study, we present the design, construction, and characterization of a 40 m3 UV-irradiated fluorinated ethylene propylene (FEP) environmental chamber developed to investigate Hg oxidation under controlled, atmospherically relevant conditions. The chamber is equipped with a suite of analytical instruments, including a dual-channel Hg analysis system with SI-traceable calibration, a heated Reactive Mercury Active System (RMAS), broadband cavity-enhanced absorption spectroscopy (BBCEAS) instruments, and additional gas analyzers for monitoring oxidants and trace gases. Characterization experiments were conducted to quantify residence time, mixing, and wall loss rates for key atmospheric constituents. The system provides a flexible platform for studying Hg oxidation mechanisms involving compounds such as hydroxyl radical (OH), ozone (O3), and bromine radicals (Br). Vigorous characterization of the atmospheric simulation chamber will allow determination of uncertainties in atmospheric Hg chemistry and improve global chemical transport models.