Furthering information from OH and HO2 +RO2 observations using a high resolution time of flight mass spectrometer
R. L. Mauldin III1,2, M. P. Rissanen1, T. Petäjä1, and M. Kulmala11Department of Physics, University of Helsinki, P.O. Box 64, 00014, Finland 2Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado
Received: 18 Dec 2015 – Accepted for review: 22 Dec 2015 – Discussion started: 18 Jan 2016
Abstract. An instrument has been developed which allows an entire suite of oxidation products (H2SO4 and Extremely Low Volatile Organic Compounds, ELVOCs) to be measured along with the concentrations of the key radical species OH and HO2 +RO2. The system combines the techniques for chemical conversion of OH or HO2 +RO2 into H2SO4 together with nitrate ion (NO3-) Chemical Ionization (CI) and Atmospheric Pressure interface - Time of Flight Mass Spectrometer (NO3- CI-APi-ToF) which has been previously used for the detection of ELVOCs and a few other oxygenated organic species. The system exhibits the same sensitivity towards OH or HO2 +RO2 as previous quadrupole chemical ionization (CIMS) measurements with limits of detection of ~2 x 105 and ~2 x 106 molecule cm-3 for OH and HO2+RO2 respectively. Unlike previous CIMS measurements, the use of a NO3- CI-APi-ToF allows the acquisition of the entire mass spectrum at high resolution with each measurement, allowing one to see how the organic species behave when the sample flow is perturbed with reagent gasses (SO2 or NO). While the combination of these measurements into one instrument is of great practical value, it is the combination of these data within the spectra obtained in each mode that extends the information far beyond the measurements themselves.
Mauldin III, R. L., Rissanen, M. P., Petäjä, T., and Kulmala, M.: Furthering information from OH and HO2 +RO2 observations using a high resolution time of flight mass spectrometer, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2015-398, 2016.