Project overview

Trop-ClOC addresses a fundamental yet highly unconstrained question in atmospheric chemistry: What is the impact of atomic chlorine on the composition of the troposphere? For decades it has been suggested that chlorine atoms (Cl) play a role in tropospheric oxidation chemistry, yet current estimates of its global mean concentration range over two orders of magnitude making atomic Cl either globally insignificant or a major oxidant. A lack of observational constraints has hampered our ability to pin down the true impact. Recent measurements of significant concentrations of previously undetected tropospheric Cl atom sources (e.g. ClNO2) have surprised the atmospheric chemistry community. The inclusion of these sources in regional and global chemistry models has indicated that Cl atoms are an important driver of tropospheric oxidation, with implications for air quality, climate and ecosystem health. However, the lack of rigorous observations required to constrain Cl atom concentrations have made definitive evaluation impossible. The aim of Trop-ClOC is to develop and deploy new measurement capability to provide a definitive constraint on local tropospheric Cl oxidation, enabling a more detailed and accurate evaluation of the impact of Cl chemistry than has been possible hitherto.