A large source of atomic chlorine from ClNO2 photolysis at a UK landfill site

Nitryl chloride (ClNO 2) acts as a source of highly reactive chlorine atoms as well as an important NO x reservoir. Measurements of ClNO 2 at an operational U.K. landfill site are reported here for the first time. A peak concentration of 4 ppb of ClNO 2 was found with a peak mean nighttime maximum of 0.9 ppb. Using models based upon the photolysis of observed ClNO 2 and atmospheric chlorine chemistry, chlorine atom concentrations reaching in excess of 1.20 × 10 5 molecules/cm 3 in the early morning following sunrise are calculated. These concentrations are approximately 10 times higher than previously reported in the United Kingdom, suggesting a significant impact on the oxidizing capacity around such sites. Given the ubiquity of landfill sites regionally and globally, and the large abundances of Cl atoms from the photolysis of ClNO 2, chlorine chemistry has a significant impact on ozone formation and volatile organic compounds oxidation as shown by WRF-Chem modeling.