Articles | Volume 8, issue 7
Atmos. Meas. Tech., 8, 2945–2959, 2015
https://doi.org/10.5194/amt-8-2945-2015
Atmos. Meas. Tech., 8, 2945–2959, 2015
https://doi.org/10.5194/amt-8-2945-2015

Research article 22 Jul 2015

Research article | 22 Jul 2015

A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: characterization from the 2013 southern oxidant and aerosol study

P. Brophy and D. K. Farmer P. Brophy and D. K. Farmer
  • Department of Chemistry, College of Natural Sciences, Colorado State University, 1872 Campus Delivery, Fort Collins, CO 80523, USA

Abstract. A novel configuration of the Aerodyne high resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI) HR-TOF-CIMS is presented and described along with data collected at the Southern Oxidant and Aerosol Study (SOAS) during the summer of 2013. The calibration system and reduced pressure gas phase inlet are characterized. The average limit of detection and limit of quantification for formic acid during SOAS are 82 and 863 ppt, respectively, corresponding to an average sensitivity of 13 ± 5 Hz ppt−1. Hourly background determinations and calibrations are shown to be essential for tracking instrument performance and accurately quantifying formic acid. Maximum daytime formic acid concentrations of 10 ppb are reported during SOAS, and a strong diel cycle is observed leading to nighttime concentrations below the limit of quantification. Other species presented exhibit diel behavior similar to formic acid. The concept of the mass defect enhancement plot and the use of signal-to-noise are described in detail as a method for investigating HR-TOF-CIMS spectra in an effort to reduce data complexity.

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Short summary
A novel configuration of the Aerodyne high resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI) HR-TOF-CIMS is presented and described along with data collected at the Southern Oxidant and Aerosol Study (SOAS) during the summer of 2013. Formic acid and other relevant species are presented, and they exhibit a strong diel cycle being rapidly produced during the day and dropping below the limit of detection at night.