Characterization of a thermal decomposition chemical ionization mass spectrometer for the measurement of peroxy acyl nitrates (PANs) in the atmosphere

Abstract

Abstract. This paper presents a detailed laboratory characterization of a thermal dissociation chemical ionization mass spectrometer (TD-CIMS) for the atmospheric measurement of Peroxyacetyl nitrate (PAN) and its homologues (PANs). PANs are efficiently dissociated in a heated inlet and the resulting peroxy acyl radicals are reacted with I − ions in a flow tube. The mass spectrometer detects the corresponding carboxylate ions. PAN, peroxypropionyl nitrate (PPN), peroxyisobutyryl nitrate (PiBN), peroxy-n-butyryl nitrate (PnBN), peroxyacryloyl nitrate (APAN), peroxycrotonyl nitrates (CPAN) and peroxymethacryloyl nitrate (MPAN) were cross-calibrated with both a dual channel GC/ECD and a total odd-nitrogen (NO y ) instrument for the NCAR TD-CIMS' typical aircraft operation conditions. In addition, the instrument sensitivity to a number of more exotic PANs (peroxyhydroxyacetyl nitrate, methoxyformyl peroxynitrate, and peroxybenzoyl nitrate) was evaluated qualitatively by comparisons with a long-path FTIR instrument.The sensitivity for PPN is slightly higher than that of PAN. Larger aliphatic and olefinic PAN compounds generally showed lower sensitivities. We postulate that these differences are owing to secondary reactions in the thermal decomposition region, which either reduce the yield of peroxy acyl radicals or cause losses of these radicals through intramolecular decomposition. The relative importance of these secondary reactions varies considerably between different PAN species.Correspondence to: F. M. Flocke (ffl@ucar.edu)Results also indicate that the reaction of the larger peroxy acyl radicals with the ion-water cluster, I − (H 2 O)n proceeds about an order of magnitude faster than with I − alone, as has been observed for peroxy acetyl radicals. Sensitivity variations among the individual PAN species at very low water vapor were observed. The results call for careful evaluation of each PAN species to be measured and for each desired operating condition of a TD-CIMS instrument.

Development of a photochemical source for the production and calibration of acyl peroxynitrate compounds

“…3b. This dependence of TD-CIMS sensitivity on the inlet dissociator temperature has been previously reported in multiple studies (Mielke and Osthoff, 2012;Furgeson et al, 2011;Zheng et al, 2011). The sensitivity dependence reported in this work is specific to this particular inlet design; is largely controlled by a combination of the residence time, temperature, and pressure field in the inlet dissociator; and is system specific.…”

“…An increasingly popular method is thermal-dissociation chemical ionization mass spectrometry (TD-CIMS) for the measurement of APNs (Slusher et al, 2004;Phillips et al, 2013;Zheng et al, 2011). Comparisons of the TD-CIMS method with other techniques, such as GC and TD-LIF, show reasonably good agreement (Wooldridge et al, 2010;Tyndall et al, 2005).…”

Peroxyacetyl nitrate (PAN) and peroxyacetic acid (PAA) measurements by iodide chemical ionisation mass spectrometry: first analysis of results in the boreal forest and implications for the measurement of PAN fluxes

“…for use in eddy correlation studies of PAN deposition (Turnipseed et al, 2006;Wolfe et al, 2009). Whilst calibration and airmatrix artefacts associated with the measurement of PAN (and other PANs) with this technique have received some attention (Zheng et al, 2011;Mielke and Osthoff, 2012) here we focus on the discovery that PAA is also converted to the acetate ion via reaction with I − and, when attempting to measure PAN, represents a non-trivial source of acetate ion signal both in terms of magnitude and variability. A number of studies comparing ICIMS to other methods of PAN detection, i.e.…”

Estimating N<sub>2</sub>O<sub>5</sub> uptake coefficients using ambient measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub> and particle-phase nitrate

“…The CIMS instrument was constructed by THS Instruments, Georgia, USA and is based on the CIMS technique described by Slusher et al (2004) and Zheng et al (2011). No indication of the production of ClNO 2 on the inlet walls was observed.…”