Articles | Volume 8, issue 1
Atmos. Meas. Tech., 8, 411–420, 2015

Special issue: Uintah Basin Winter Ozone Studies (ACP/AMT inter-journal SI)

Atmos. Meas. Tech., 8, 411–420, 2015

Research article 26 Jan 2015

Research article | 26 Jan 2015

PTR-QMS versus PTR-TOF comparison in a region with oil and natural gas extraction industry in the Uintah Basin in 2013

C. Warneke1,2, P. Veres1,2, S. M. Murphy3, J. Soltis3, R. A. Field3, M. G. Graus1,2,*, A. Koss1,2, S.-M. Li4, R. Li1,2, B. Yuan1,2, J. M. Roberts2, and J. A. de Gouw1,2 C. Warneke et al.
  • 1Cooperative Institute for Research in Environmental Sciences, Univ. of Colorado, Boulder, CO, USA
  • 2NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, USA
  • 3Department of Atmospheric Science, University of Wyoming, Laramie, WY, USA
  • 4Air Quality Process Research Division, Environment Canada, Toronto, ON, Canada
  • *now at: Institute of Meteorology and Geophysics, Innsbruck University, Innsbruck, Austria

Abstract. Here we compare volatile organic compound (VOC) measurements using a standard proton-transfer-reaction quadrupole mass spectrometer (PTR-QMS) with a new proton-transfer-reaction time of flight mass spectrometer (PTR-TOF) during the Uintah Basin Winter Ozone Study 2013 (UBWOS2013) field experiment in an oil and gas field in the Uintah Basin, Utah. The PTR-QMS uses a quadrupole, which is a mass filter that lets one mass to charge ratio pass at a time, whereas the PTR-TOF uses a time of flight mass spectrometer, which takes full mass spectra with typical 0.1 s–1 min integrated acquisition times. The sensitivity of the PTR-QMS in units of counts per ppbv (parts per billion by volume) is about a factor of 10–35 times larger than the PTR-TOF, when only one VOC is measured. The sensitivity of the PTR-TOF is mass dependent because of the mass discrimination caused by the sampling duty cycle in the orthogonal-acceleration region of the TOF. For example, the PTR-QMS on mass 33 (methanol) is 35 times more sensitive than the PTR-TOF and for masses above 120 amu less than 10 times more. If more than 10–35 compounds are measured with PTR-QMS, the sampling time per ion decreases and the PTR-TOF has higher signals per unit measuring time for most masses. For UBWOS2013 the PTR-QMS measured 34 masses in 37 s and on that timescale the PTR-TOF is more sensitive for all masses. The high mass resolution of the TOF allows for the measurements of compounds that cannot be separately detected with the PTR-QMS, such as oxidation products from alkanes and cycloalkanes emitted by oil and gas extraction. PTR-TOF masses do not have to be preselected, allowing for identification of unanticipated compounds. The measured mixing ratios of the two instruments agreed very well (R2 ≥ 0.92 and within 20%) for all compounds and masses monitored with the PTR-QMS.