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https://doi.org/10.5194/amt-2016-407
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
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, Charles A. Brock1, Daniel M. Murphy1, Donna T. Sueper3, André Welti1,2,b, and Ann M. Middlebrook1 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 Re search Inc., Billerica, MA 01821, USA
aNow at: Universities Space Research Association, Columbia, MD 21046, USA and NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamic Laboratory, Greenbelt, MD 20771, USA
bNow 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-ToF-AMS) to investigate collection efficiency (CE) while obtaining non-refractory aerosol chemical composition measurements during the Southeast Nexus (SENEX) campaign. In this instrument, particles typically larger than ~ 250 nm in vacuum aerodynamic diameter scatter light from an internal laser beam and trigger saving individual particle mass spectra. Over 33,000 particles are characterized as either prompt (27 %), delayed (15 %), or null (58 %), according to the appearance time and intensity of their mass spectral signals. The individual particle mass from the spectra is proportional to the mass derived from the vacuum aerodynamic diameter determined by the light scattering signals (dva-LS) rather than the traditional particle time-of-flight (PToF) size (dva). The delayed particles capture about 80 % of the total chemical mass compared to prompt ones. 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 on the vaporizer and vaporized later on a lower temperature surface within the confines of the ionization source. Because delayed particles are detected at a later time by the mass spectrometer than expected, they can affect the interpretation of PToF mass distributions especially at the larger sizes. CE, measured by the average number or mass fractions of particles optically detected that have measureable mass spectra, varied significantly (0.2–0.9) in different air masses. Relatively higher null fractions and corresponding lower CE for this study may have been related to the lower sensitivity of the AMS during SENEX. The measured CE generally agreed with the CE parameterization based on ambient chemical composition, including for acidic particles that had a higher CE as expected from previous studies.

Citation: Liao, J., Brock, C. A., Murphy, D. M., Sueper, D. T., Welti, A., and Middlebrook, A. M.: Single particle measurements of bouncing particles and in-situ collection efficiency from an airborne aerosol mass spectrometer (AMS) with light scattering detection, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2016-407, in review, 2017.
Jin Liao et al.
Jin Liao et al.

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Short summary
The Aerodyne aerosol mass spectrometer (AMS) has emerged as a widely used method for measuring the real-time, submicron, non-refractory 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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