On quantitative measurements of peroxycarboxylic nitric anhydride mixing ratios by thermal dissociation chemical ionization mass spectrometry

Abstract

Thermal dissociation chemical ionization mass spectrometry (TD-CIMS) has become an increasingly popular tool for rapid and sensitive quantification of peroxycarboxylic nitric anhydrides (PANs), which are important trace gas constituents of the troposphere. In TD-CIMS, the PANs are thermally dissociated in a heated inlet to NO 2 and peroxyacyl radicals, which are converted in electron transfer reactions with iodide reagent ions to the corresponding carboxylate anions. Here, we evaluate the performance of the TD-CIMS method in the presence of interferences that occur in polluted air masses. Response factors of the TD-CIMS were determined using laboratory-generated air samples and parallel measurements of NO 2 and ΣPAN by blue diode laser thermal dissociation cavity ring-down spectroscopy (TD-CRDS) and of NO y by NO-O 3 chemiluminescence (CL). The TD-CIMS was less sensitive to peroxymethacryloyl nitric anhydride (MPAN) than to other PANs tested, which was rationalized by differences in the temperature dependent loss rates of the peroxyacyl radicals in the heated inlet. To track matrix effects, photochemically generated 13C-labeled PAN was continuously added as an internal standard. The presence of NO or NO 2 in the sample gas mixture resulted in signal suppression, which could be corrected using the internal standard. The presence of organic acids resulted in a redistribution of count intensity between carboxylate anions, impacting the instrument's ability to accurately quantify PANs other than peroxyacetic nitric anhydride under moderately polluted conditions.