Are We Measuring What We Think We’re Measuring? Assessing the ACSM’s Sampling Efficiency

Arthur J. Sedlacek, Maria Zawadowicz, Ogochukwu Enekwizu, Ernie R. Lewis, AMIE DOBRACKI, Brookhaven National Laboratory

     Abstract Number: 395
     Working Group: Carbonaceous Aerosols

Abstract
Biomass burning injects 16-34 Tg of particulate matter into Earth’s atmosphere each year and is a major source of black carbon (BC) and organic aerosols (OA). In this study we determined the sampling efficiency of the Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM; Aerodyne) for biomass burning relevant compounds such as, sucrose, levoglucosan, and oleic acid using two different experimental setups. Initially, we examined the sampling efficiency for pure aerosolized particles with electrical mobility diameters of 100, 200, 300, and 400 nm. The second set of experiments evaluated the sampling efficiency for levoglucosan and oleic acid coatings, varying in thickness between 20 and 50 nm on 150 nm BC particles to ascertain if the ACSM effectively samples a diverse range of organic substances, despite variations in their size, chemical composition, and phase state. Our results show that the sampling efficiency is greatest (80-90 %) for uncoated 200 nm sucrose, levoglucosan, and oleic acid particles, whereas the other electrical mobility diameters were sampled less efficiently (60-70 %). In the coated particle experiments, we found that there were no discernible differences in sampling efficiency when the coating thicknesses of levoglucosan and oleic acid varied between 20 and 50 nm. However, we did identify slight differences in mass spectra when comparing the spectra of pure aerosolized particles to the spectra of coated particles, suggesting that in the presence of refractory compounds, the organic components are vaporized differently than pure OA.