Observation of ClNO2 in a mid-continental urban environment.

In the troposphere, nitryl chloride (ClNO2), produced from uptake of dinitrogen pentoxide (N2O5) on chloride containing aerosol, can be an important nocturnal reservoir of NO(x) (= NO + NO2) and a source of atomic Cl, particularly in polluted coastal environments. Here, we present measurements of ClNO2 mixing ratios by chemical ionization mass spectrometry (CIMS) in Calgary, Alberta, Canada over a 3-day period. The observed ClNO2 mixing ratios exhibited a strong diurnal profile, with nocturnal maxima in the range of 80 to 250 parts-per-trillion by volume (pptv) and minima below the detection limit of 5 pptv in the early afternoon. At night, ClNO2 constituted up to 2% of odd nitrogen, or NO(y). The peak mixing ratios of ClNO2 observed were considerably below the modeled integrated heterogeneous losses of N2O5, indicating that ClNO2 production was a minor pathway compared to heterogeneous hydrolysis of N2O5. Back trajectory analysis using HYSPLIT showed that the study region was not influenced by fresh injections of marine aerosol, implying that aerosol chloride was derived from anthropogenic sources. Molecular chlorine (Cl2), derived from local anthropogenic sources, was observed at mixing ratios of up to 65 pptv and possibly contributed to formation of aerosol chloride and hence the formation of ClNO2.

Measurements of total peroxy and alkyl nitrate abundances in laboratory-generated gas samples by thermal dissociation cavity ring-down spectroscopy.

A novel measurement technique, thermal dissociation cavity ring-down spectroscopy (TD-CRDS), for rapid (1 s time resolution) and sensitive (precision approximately 100 parts per trillion by volume (10(-12); pptv)) quantification of total peroxy nitrate (SigmaPN) and total alkyl nitrate (SigmaAN) abundances in laboratory-generated gas mixtures is described. The organic nitrates are dissociated in a heated inlet to produce NO(2), whose concentration is monitored by pulsed-laser CRDS at 532 nm. Mixing ratios are determined by difference relative to a cold inlet reference channel. Conversion of laboratory-generated mixtures of AN in zero air (at an inlet temperature of 450 degrees C) is quantitative over a wide range of mixing ratios (0-100 parts per billion by volume (10(-9), ppbv)), as judged from simultaneous measurements of NO(y) using a commercial NO-O(3) chemiluminescence monitor. Conversion of PN is quantitative up to about 4 ppbv (at an inlet temperature of 250 degrees C); at higher concentrations, the measurements are affected by recombination reactions of the dissociation products. The results imply that TD-CRDS can be used as a generic detector of dilute mixtures of organic nitrates in air at near-ambient concentration levels in laboratory experiments. Potential applications of the TD-CRDS technique in the laboratory are discussed.