The determination of ClNO 2 via thermal dissociation–tunable infrared laser direct absorption spectroscopy

Nitryl chloride (ClNO 2 ) is a reservoir species of chlorine atoms and nitrogen oxides, both of which play important roles in atmospheric chemistry. To date, all ambient ClNO 2 observations have been obtained by chemical ionization mass spectrometry (CIMS). In this work, thermal dissociation–tunable infrared laser direct absorption spectrometry (TD-TILDAS) is shown to be a viable method for quantifying ClNO 2 in laboratory and field settings. This technique relies on the thermal dissociation of ClNO 2 to create chlorine radicals, which undergo fast reactions with hydrocarbons to produce hydrogen chloride (HCl) that is detectable by the TILDAS instrument. Complete quantitative conversion of ClNO 2 to HCl was achieved at temperatures > 400 °C, achieving 1 Hz measurement precision of 11 ± 1 pptv (3 σ limits of detection of 34 ± 2 pptv) during laboratory comparisons with other ClNO 2 detection methods. After blank and line loss corrections, method accuracy is estimated to be within ± 5 %. Performance metrics of TD-TILDAS during ambient sampling were a 1 Hz precision of 19 ± 1 pptv and 3 σ limits of detection of 57 ± 3 pptv, which is directly comparable to previously reported ClNO 2 detection by quadrupole CIMS. Thus, TD-TILDAS can provide an alternative analytical approach for a direct measurement of ClNO 2 that can complement existing datasets and future studies. The quantitative nature of TD-TILDAS also makes it a potentially useful tool for the calibration of CIMS instruments. However, interpretation of ambient data may be complicated by potential interferences from unaccounted-for sources of thermolabile chlorine, such as ClNO, chloramines, and organochlorides.

Abstract licence: CC BY

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