The first nitryl chloride (ClNO 2 ) measurements in the UK were made during the summer 2012 ClearfLo campaign with a chemical ionization mass spectrometer, utilizing an I À ionization scheme.Concentrations of ClNO 2 exceeded detectable limits (11 ppt) every night with a maximum concentration of 724 ppt. A diurnal profile of ClNO 2 peaking between 4 and 5 A.M., decreasing directly after sunrise, was observed. Concentrations of ClNO 2 above the detection limit are generally observed between 8 P.M. and 11 A.M. Different ratios of the production of ClNO 2 :N 2 O 5 were observed throughout with both positive and negative correlations between the two species being reported. The photolysis of ClNO 2 and a box model utilizing the Master Chemical Mechanism modified to include chlorine chemistry was used to calculate Cl atom concentrations. Simultaneous measurements of hydroxyl radicals (OH) using low pressure laser-induced fluorescence and ozone enabled the relative importance of the oxidation of three groups of measured VOCs (alkanes, alkenes, and alkynes) by OH radicals, Cl atoms, and O 3 to be compared. For the day with the maximum calculated Cl atom concentration, Cl atoms in the early morning were the dominant oxidant for alkanes and, over the entire day, contributed 15%, 3%, and 26% toward the oxidation of alkanes, alkenes, and alkynes, respectively.

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