Emissions and marine boundary layer concentrations of unregulated chlorocarbons measured at Cape Point, South Africa

Unregulated chlorocarbons - here defined as dichloromethane (CH2Cl2), perchloroethene (C2Cl4), chloroform (CHCl3) and methyl chloride (CH3Cl) – are gases not regulated by the Montreal Protocol. While CH3Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could pose a significant threat to the recovery of the ozone layer. Despite this, there remain many regions for which no atmospheric monitoring exists, leaving gaps in our understanding of global emissions. Here, we report on a new time-series of chlorocarbon measurements from Cape Point, South Africa for 2017, which represent the first published high-frequency measurements of these gases from Africa. For CH2Cl2 and C2Cl4, the majority of mole fraction enhancements were observed from the north, consistent with anthropogenically modified air from Cape Town, while for CHCl3 and CH3Cl, we found evidence for both oceanic and terrestrial sources. Using an inverse method, we estimated emissions for south western South Africa (SWSA). For each chlorocarbon, SWSA accounted for less than 1% of global emissions. For CH2Cl2 and C2Cl4, we extrapolated using population statistics and found South African emissions of 8.9 (7.4 - 10.4) Gg yr-1 and 0.80 (0.64 - 1.04) Gg yr-1, respectively.