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

Abstract

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 ∼ 280 nm in vacuum aerodynamic diameter. Over 33 000 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 (d va-LS ) but not to that from the particle time-of-flight (PToF) diameter (d va-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 d va-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 d va-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.

An Odd Oxygen Framework for Wintertime Ammonium Nitrate Aerosol Pollution in Urban Areas: NOx and VOC Control as Mitigation Strategies

“…These results are compared to observations of trace gas species from the recent Uintah Basin Winter Ozone Study, where a major PCAP in January 2013 led to elevated levels of O 3 (Ahmadov et al, 2015;Edwards et al, 2014). Measurement techniques for both campaigns are described in detail in Text S1 (Lee et al, 2014;Liao et al, 2017;Wild et al, 2014;Wild et al, 2016).…”

Evidence in biomass burning smoke for a light-absorbing aerosol with properties intermediate between brown and black carbon

“…Measurements of the non-refractory aerosol chemical composition were obtained with a compact, time-offlight aerosol mass spectrometer (c-ToF AMS) equipped with an internal light-scattering module (Liao et al 2017). The vaporizer temperature was roughly 600 C. Mass spectra were acquired while cycling through different data acquisition modes, with bulk mass spectra recorded approximately every 6.5 s plus mass distributions and light-scattering single particle data recorded roughly once a minute.…”

Airborne and ground-based observations of ammonium nitrate dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah

“…The TO-AMS was also equipped with a light scattering module (LS) that provided a more accurate size information in the range 200-1000 nm and on the collection efficiency (Liao et al, 2017). A CE of 1 was used for this analysis based on the light scattering (see SI).…”