Aerodyne Aerosol Mass Spectrometer Collection Efficiency Measurements of Smoke from Laboratory Burns of Wildland Fuels
ANN M. MIDDLEBROOK, Alessandro Franchin, NOAA Chemical Sciences Laboratory
Abstract Number: 68
Working Group: Instrumentation and Methods
Abstract
One of the key uncertainties in the Aerodyne Aerosol Mass Spectrometer (AMS) and Aerosol Chemical Speciation Monitor (ACSM) measurements is the collection efficiency (CE), which incorporates aerodynamic lens transmission, particle beam focusing (mainly for AMS instruments), and particle bounce off of the vaporizer. Laboratory and field studies indicate that particle phase is an important factor in whether or not particles bounce off the vaporizer prior to evaporating. While an algorithm to calculate the bounce-related CE based on the inorganic components and sampling line relative humidity has been used with fairly reproducible results, the organic effect on CE is less well-understood. Past evaluation of field measurements with increasing organic mass have not shown any specific effects of the organic composition. Yet, there might be hints of differing collection efficiencies for urban secondary organic aerosol (SOA) and biomass burning OA. Laboratory measurements from fresh SOA indicate that the CE decreases with increasing fraction of oxidized ions.
In the fall of 2016, we performed experiments at the U. S. Forest Service Missoula Fire Sciences Laboratory aimed at examining the properties of fresh smoke from a variety of wildland fuels with several different instruments. We used a compact time-of-flight aerosol mass spectrometer equipped with a light-scattering module and an AP240 data acquisition card, which can obtain light scattering data and corresponding mass spectra from single particles (LSSP). In LSSP mode, a particle detected by the laser may or may not have detectable mass spectra and this metric defines the CE measured by light scattering or CELS. Here we present measurements of CELS for fresh, diluted smoke and smoke that had passed through a thermodenuder and/or a small oxidation chamber. We will present these results and comparisons of them with prior CE studies of organic aerosols.