Photocatalytic Chlorine Production From Iron Chlorides in Atmospheric Aerosols: Strategies for Quantifying Methane and Tropospheric Ozone Control

It was recently discovered that chlorine is produced photocatalytically from mineral dust-sea spray aerosols, impacting methane and tropospheric ozone, and an evaluation was made of the climate and environmental impact of a chlorine-based intervention to draw down methane. The generation of chlorine by the iron chlorides Fe(III) (Formula presented.) will also occur due to iron present in shipping plumes. To study efficiency and environmental implications, there is a need for additional information about the behavior of the process under a range of atmospheric conditions. Here, we use box modeling to evaluate whether it is possible to experimentally observe this mechanism in a ship's plume, or in a plume of pure iron dust, emitted for example, from a tower. Detection limits for Cl, (Formula presented.), HOCl, ClO, (Formula presented.), (Formula presented.), CO, (Formula presented.), (Formula presented.), and (Formula presented.) are determined based on values from the literature. We find that the most promising and low-cost experimental indicators of chlorine atom production are the concentration of photoactive iron and the CO:ethane ratio, and (Formula presented.) is a useful indicator if cost is not a limitation. For ships with high (Formula presented.) emissions, (Formula presented.), and (Formula presented.) could also potentially be used, and for towers emitting Fe without (Formula presented.) the concentration of HOCl and ClO could be used. (Formula presented.) is a very direct method to detect methane removal, but only gives a clear signal for high iron emissions.