Characterization of a thermal decomposition chemical ionization mass spectrometer for the measurement of peroxy acyl nitrates (PANs) in the atmosphere 1Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
08 Jul 2011
2Coorperative Institute for Research in Environmental Science, University of Colorado, Boulder, Colorado, USA
3Chemical Sciences Division, Earth System Research Lab, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
4School of Earth and Atmospheric Science, Georgia Institute of Technology, Atlanta, Georgia, USA
*now at: Northrop Grumman Aerospace Systems, Redondo Beach, California, USA
Received: 31 January 2011 – Published in Atmos. Chem. Phys. Discuss.: 11 March 2011 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
(NOy) 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.
Revised: 17 June 2011 – Accepted: 22 June 2011 – Published: 08 July 2011
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.
Results also indicate that the reaction of the larger peroxy acyl radicals
with the ion-water cluster, I−(H2O)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.
Citation: Zheng, W., Flocke, F. M., Tyndall, G. S., Swanson, A., Orlando, J. J., Roberts, J. M., Huey, L. G., and Tanner, D. J.: Characterization of a thermal decomposition chemical ionization mass spectrometer for the measurement of peroxy acyl nitrates (PANs) in the atmosphere, Atmos. Chem. Phys., 11, 6529-6547, doi:10.5194/acp-11-6529-2011, 2011.