Performance characteristics of a proton-transfer-reaction mass spectrometer (PTR-MS) derived from laboratory and field measurements

Abstract

Volatile organic compounds (VOCs) play an important role in the formation of ozone and aerosols in the atmosphere. In an increasing number of field campaigns the proton-transfer-reaction mass spectrometer (PTR-MS) has proven to be a useful and fast tool for measuring VOCs and studying the relevant atmospheric processes. This work describes laboratory and field measurements with two different versions of the PTR-MS and presents important instrument specific features. The temperature stabilization and the change of the gasket material in the newer version significantly improved the performance of the instrument, as demonstrated by periodical background measurements under field conditions. The investigation of the mass discrimination illustrated the necessity of an elaborate verification. The humidity dependence of benzene was substantially lower than in former studies, which used higher drift tube pressures, but it is still higher than predicted by a simple dimer/monomer equilibrium model. An instrument comparison with a fluorescent technique was performed for formaldehyde and showed differences between pure formaldehyde calibration gases and complex ambient air samples. An intercomparison of two PTR-MSs measuring ambient air yielded satisfactory results after calibration for most of the considered masses. Comparing PTR-MS and gas chromatograph measurements of aromatic compounds, revealed a good agreement for conditions of fresh anthropogenic emissions. In photochemically aged air, many masses detected by the PTR-MS are not only influenced by anthropogenically and biogenically emitted but also oxidized VOCs. © 2004 Elsevier B.V. All rights reserved.