Ubiquity of ClNO₂ in the urban boundary layer of Calgary, Alberta, Canada

Abstract

The role of nitryl chloride (ClNO2) as a nocturnal nitrogen oxide reservoir species and chlorine atom precursor is well established for polluted coastal areas, but its role at midcontinental locations is less clear. In this paper, intermittent measurements over the course of several seasons of ClNO2 mixing ratios by iodide ion chemical ionization mass spectrometry in Calgary, Alberta, Canada, are presented. Mixing ratios were highly variable between nights and seasons and depended on the abundances of precursors and meteorological conditions. The lowest ClNO2 mixing ratios (nocturnal maximum of 30 parts per trillion by volume (pptv)) were observed in the summer, rationalized by losses of the nitrate radical (NO3) that were more efficient than in the other months. Higher ClNO2 mixing ratios (up to 330 pptv) were observed in the winter and spring months but varied between nights. In the fall, ClNO2 mixing ratios increased from night to night following the application of salt to roads. The ClNO2 yield relative to the amount of NO3 produced from oxidation of NO2 by O3 ranged from 0.1% to 4.5% (10th and 90th percentiles, median 1.0%). The ClNO2 yield relative to N2O5 consumed by heterogeneous reactions was estimated using a time-integrated box model and ranged from 0.5% to 12.1% (10th and 90th percentiles, median 3.4%). The ubiquity of ClNO2 implies that the chlorine atom needs to be considered as an oxidant in high-latitude urban environments in winter.

Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia

“…8a, right-hand axis), of which 600 pptv was produced before midnight. The amount of ClNO 2 produced relative to this amount, φ'(ClNO 2 ), was very small (median 0.17 %, maximum 5.4 % on the morning of 2 August) and considerably less than reported by our group for Calgary (median 1.0 %) (Mielke et al, 2016) and Pasadena, CA (median 12 %) (Mielke et al, 2013).…”

“…Figure 10 shows the instantaneous radical production rates of Cl and OH, P (Cl) = j (ClNO 2 ) × [ClNO 2 ] and P (OH) from reaction of O( 1 D)+H 2 O. The latter was calculated from an assumed steady state in O( 1 D) with respect to its production from O 3 photolysis and reactions with N 2 , O 2 , and H 2 O as described by Mielke et al (2016). This analysis does not account for OH radical production from photolysis of nitrous acid or aldehydes and, hence, overestimates the importance of Cl radicals.…”

Fast heterogeneous N<sub>2</sub>O<sub>5</sub> uptake and ClNO<sub>2</sub> production in power plant and industrial plumes observed in the nocturnal residual layer over the North China Plain

“…Elevated ClNO 2 mixing ratios were firstly observed in several polluted coast regions (for instance, the coasts of Texas and California, and the Los Angeles Basin), resulting from the strong emission of NO x and abundant chloride from sea salt aerosols (Osthoff et al, 2008;Mielke et al, 2013;Tham et al, 2014). Recently, significant ClNO 2 production was also observed in some inland areas (such as Colorado, Hessen, and Alberta), with a mixing ratio of up to several hundreds of pptv or even exceeding 1.0 ppbv (e.g., Thornton et al, 2010;Mielke et al, 2011Mielke et al, , 2016Phillips et al, 2012;Riedel et al, 2013;Faxon et al, 2015). Anthropogenic sources of chlorine including coal combustion in power plants, industries, and biomass burning may potentially facilitate ClNO 2 production .…”

Formation and emission of hydrogen chloride in indoor air

“…20 Recent work has shown that chlorine atoms oxidize volatile organic compounds (VOCs) and produce ozone more efficiently than hydroxyl radicals, even in small quantities. 2,21,[25][26][27][28] Production of chlorine atoms results from photolysis and oxidation reactions of precursor molecules. 23 Both scenarios have significant air quality and environmental implications; thus, monitoring of chlorine atoms is essential.…”