The first UK measurements of nitryl chloride using a chemical ionization mass spectrometer in central London in the summer of 2012, and an investigation of the role of Cl atom oxidation

Abstract

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.

Production of N<sub>2</sub>O<sub>5</sub> and ClNO<sub>2</sub> in summer in urban Beijing, China

“…Tham et al, 2016). However, the ratios are substantially higher than those measured in other megacities, e.g., Hong Kong (0.1-2.0; Wang et al, 2016), London (0.02-2.4;Bannan et al, 2015), and Los Angeles, California (0.2-10.0; Mielke et al, 2013). These results indicate ubiquitously high ClNO 2 /N 2 O 5 ratios in the NCP, consistent with another measurement in suburban Beijing , which might result from the high ClNO 2 production rate due to high aerosol loadings.…”

“…Previous studies have found that N 2 O 5 and ClNO 2 were generally positively correlated in predominantly continental air masses, whereas they were negatively correlated in marine air masses with high chloride content (Bannan et al, 2015). Phillips et al (2012) also reported large variability in N 2 O 5 and ClNO 2 correlations and ClNO 2 /N 2 O 5 ratios in air masses from continental or marine origins due to the changes in particle Cl − .…”

“…Aerosol liquid water content associated with inorganic species was estimated using the ISORROPIA-II thermodynamic equilibrium model (Nenes et al, 1998;Fountoukis and Nenes, 2007), with input data of ambient NR-PM 1 species, and RH and T at 15 m. The N 2 O 5 uptake coefficient and ClNO 2 yield can also be calculated by the parameterization proposed by Bertram and Thornton (2009). (Bannan et al, 2015;Thornton et al, 2010) and the residual layer at Mt. Tai (Z. .…”

“…A large amount of ClNO 2 was first observed in polluted coastal regions owing to the abundant chloride from sea salt aerosol, for example in the Gulf of Mexico and the Los Angeles basin Riedel et al, 2012;Kercher et al, 2009). High levels of ClNO 2 from anthropogenic chloride sources were also reported in some inland areas (Thornton et al, 2010;Mielke et al, 2011;Phillips et al, 2012Phillips et al, , 2016Bannan et al, 2015). More recently some studies in Hong Kong Brown et al, 2016a;Wang et al, 2016) and in the North China Plain (NCP; Tham et al, 2016;Wang et al, 2018) observed consistently high mixing ratios of N 2 O 5 and ClNO 2 .…”

“…A range of other species were calibrated after the campaign, and relative calibration factors were derived using the measured formic acid sensitivity during these calibrations as has been performed previously Bannan et al, 2014Bannan et al, , 2015.…”