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

摘要

We investigated the collection efficiency and effective ionization efficiencyfor secondary organic aerosol (SOA) particles made from -pinene +O using the single-particle capabilities of the aerosol massspectrometer (AMS). The mean count-based collection efficiency (CE) forSOA across these experiments is 0.30 (±0.04 SD), ranging from 0.25 to0.40. The mean mass-based collection efficiency (CE) is0.49 (±0.07 SD). This sub-unit collection efficiency and delayedvaporization is attributable to particle bounce in the vaporization region.Using the coupled optical and chemical detection of the light-scatteringsingle-particle (LSSP) module of the AMS, we provide clear evidence that is somewhat of a misnomer for these particles: SOAparticles measured as a part of the AMS mass distribution do not vaporizeat a slow rate; rather, they flash-vaporize, albeit often not on the initialimpact with the vaporizer but instead upon a subsequent impact with a hotsurface in the vaporization region. We also find that the effectiveionization efficiency (defined as ions per particle, IPP) decreases withdelayed arrival time. CE is not a function of particlesize (for the mobility diameter range investigated, 170–460 nm), but we didsee a decrease in CE with thermodenuder temperature,implying that oxidation state and/or volatility can affect CE for SOA. By measuring the mean ions per particle produced formonodisperse particles as a function of signal delay time, we can separatelydetermine CE and CE and thus moreaccurately measure the relative ionization efficiency (compared to ammoniumnitrate) of different particle types.