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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 10 | Copyright
Atmos. Meas. Tech., 10, 3801-3820, 2017
https://doi.org/10.5194/amt-10-3801-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 Oct 2017

Research article | 17 Oct 2017

Single-particle measurements of bouncing particles and in situ collection efficiency from an airborne aerosol mass spectrometer (AMS) with light-scattering detection

Jin Liao1,2,a,b, Charles A. Brock1, Daniel M. Murphy1, Donna T. Sueper3, André Welti1,2,c, and Ann M. Middlebrook1 Jin Liao et al.
  • 1NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO 80305, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO 80309, USA
  • 3Aerodyne Research Inc., Billerica, MA 01821, USA
  • anow at: Universities Space Research Association, Columbia, MD 21046, USA
  • bnow at: NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamic Laboratory, Greenbelt, MD 20771, USA
  • cnow at: Leibniz Institute for Tropospheric Research, Department of Physics, Leipzig, 04318, Germany

Abstract. A light-scattering module was coupled to an airborne, compact time-of-flight aerosol mass spectrometer (LS-AMS) to investigate collection efficiency (CE) while obtaining nonrefractory aerosol chemical composition measurements during the Southeast Nexus (SENEX) campaign. In this instrument, particles scatter light from an internal laser beam and trigger saving individual particle mass spectra. Nearly all of the single-particle data with mass spectra that were triggered by scattered light signals were from particles larger than ∼ 280nm in vacuum aerodynamic diameter. Over 33000 particles are characterized as either prompt (27%), delayed (15%), or null (58%), according to the time and intensity of their total mass spectral signals. The particle mass from single-particle spectra is proportional to that derived from the light-scattering diameter (dva-LS) but not to that from the particle time-of-flight (PToF) diameter (dva-MS) from the time of the maximum mass spectral signal. The total mass spectral signal from delayed particles was about 80% of that from prompt ones for the same dva-LS. Both field and laboratory data indicate that the relative intensities of various ions in the prompt spectra show more fragmentation compared to the delayed spectra. The particles with a delayed mass spectral signal likely bounced off the vaporizer and vaporized later on another surface within the confines of the ionization source. Because delayed particles are detected by the mass spectrometer later than expected from their dva-LS size, they can affect the interpretation of particle size (PToF) mass distributions, especially at larger sizes. The CE, measured by the average number or mass fractions of particles optically detected that had measurable mass spectra, varied significantly (0.2–0.9) in different air masses. The measured CE agreed well with a previous parameterization when CE > 0.5 for acidic particles but was sometimes lower than the minimum parameterized CE of 0.5.

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The Aerodyne aerosol mass spectrometer (AMS) has emerged as a widely used method for measuring the real-time, submicron, nonrefractory aerosol composition. A large uncertainty in accurate measurements with the AMS (the collection efficiency due to particle bounce) is evaluated in this paper using in situ measurements of particle light scattering. Current calculations of the collection efficiency reasonably predict this effect in acidic environments, resulting in more confidence for AMS results.
The Aerodyne aerosol mass spectrometer (AMS) has emerged as a widely used method for measuring...
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