Articles | Volume 10, issue 3
Atmos. Meas. Tech., 10, 1139–1154, 2017
https://doi.org/10.5194/amt-10-1139-2017
Atmos. Meas. Tech., 10, 1139–1154, 2017
https://doi.org/10.5194/amt-10-1139-2017

Research article 21 Mar 2017

Research article | 21 Mar 2017

Collection efficiency of α-pinene secondary organic aerosol particles explored via light-scattering single-particle aerosol mass spectrometry

Ellis Shipley Robinson1,2, Timothy B. Onasch3, Douglas Worsnop3, and Neil M. Donahue1,2 Ellis Shipley Robinson et al.
  • 1Carnegie Mellon University, Center for Atmospheric Particle Studies, Pittsburgh, PA, USA
  • 2Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
  • 3Aerodyne Research, Inc., Billerica, MA, USA

Abstract. We investigated the collection efficiency and effective ionization efficiency for secondary organic aerosol (SOA) particles made from α-pinene + O3 using the single-particle capabilities of the aerosol mass spectrometer (AMS). The mean count-based collection efficiency (CEp) for SOA across these experiments is 0.30 (±0.04 SD), ranging from 0.25 to 0.40. The mean mass-based collection efficiency (CEm) is 0.49 (±0.07 SD). This sub-unit collection efficiency and delayed vaporization is attributable to particle bounce in the vaporization region. Using the coupled optical and chemical detection of the light-scattering single-particle (LSSP) module of the AMS, we provide clear evidence that delayed vaporization is somewhat of a misnomer for these particles: SOA particles measured as a part of the AMS mass distribution do not vaporize at a slow rate; rather, they flash-vaporize, albeit often not on the initial impact with the vaporizer but instead upon a subsequent impact with a hot surface in the vaporization region. We also find that the effective ionization efficiency (defined as ions per particle, IPP) decreases with delayed arrival time. CEp is not a function of particle size (for the mobility diameter range investigated, 170–460 nm), but we did see a decrease in CEp with thermodenuder temperature, implying that oxidation state and/or volatility can affect CEp for SOA. By measuring the mean ions per particle produced for monodisperse particles as a function of signal delay time, we can separately determine CEp and CEm and thus more accurately measure the relative ionization efficiency (compared to ammonium nitrate) of different particle types.