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 (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.
Highlights
IntroductionChemical composition, and mass loading are important parameters used to estimate the impact of aerosols on direct (aerosol–radiation) and indirect (aerosol–cloud) climate effects (e.g., Ramanathan et al, 2001)
Aerosol size, chemical composition, and mass loading are important parameters used to estimate the impact of aerosols on direct and indirect climate effects (e.g., Ramanathan et al, 2001)
Particles are accelerated into the vacuum chamber at the lens exit based on their size and particle velocities are assumed to be constant by the time they reach the chopper wheel
Summary
Chemical composition, and mass loading are important parameters used to estimate the impact of aerosols on direct (aerosol–radiation) and indirect (aerosol–cloud) climate effects (e.g., Ramanathan et al, 2001). The Aerodyne aerosol mass spectrometer (AMS) is a fast time response instrument capable of quantifying sizeresolved nonrefractory aerosol chemical composition (e.g., Jayne et al, 2000; Jimenez et al, 2003; Drewnick et al, 2005; Canagaratna et al, 2007) and has been widely used to measure the real time aerosol ensemble organic, sulfate, nitrate, ammonium, and chloride (non-sea-salt) mass loadings globally (e.g., Zhang et al, 2007a; Jimenez et al, 2009). J. Liao et al.: Single-particle measurements from an airborne light-scattering AMS
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