Validation and Demonstration of the “Chemspot” Instrument for Measuring Aerosol Composition
PURUSHOTTAM KUMAR, James Hurley, Nathan Kreisberg, Braden Stump, Pat Keady, Susanne Hering, Andrew Grieshop, Gabriel Isaacman-VanWertz,
Virginia Tech Abstract Number: 360
Working Group: Instrumentation and Methods
AbstractOnline measurements of the chemical composition of particulate matter have typically relied on expensive and complex research-grade instruments based on mass spectrometry and/or chromatography. Routine monitoring necessarily relies on low-cost alternatives that can be readily operated autonomously. Yet existing methods provide limited chemical information about particulate matter. For organic aerosols, these instruments do not provide data on the degree of oxygenation of particles, a critical parameter in understanding the transformations and impacts of organic aerosols. To bridge this gap, a new instrument “Chemspot” has been developed that grows particles with water condensation, impacts them onto a passivated surface with low thermal mass, and uses stepped thermal desorption of analytes to a combination of Flame Ionization Detector (FID) & Flame Photometric Detector (FPD) and then to a CO
2 detector downstream of the FID/FPD setup. We present here the intercomparison of the “Chemspot” instrument with other reference/research-grade instruments to measure aerosol mass, volatility, and elemental ratios (O:C, S:C). We also demonstrate the capability of continuous and autonomous operation of “Chemspot” for multi-week periods. Two “Chemspot” prototypes were run autonomously in parallel, alongside an Aerosol Chemical Speciation Monitor (ACSM) and a Scanning Electrical Mobility Sizer (SEMS), sampling ambient air in Blacksburg, Virginia for two weeks. Initial results indicate that aerosol mass measured by “Chemspot” correlates well (R
2 = 0.95) with measurements using other techniques. We will further discuss in detail the accuracy and uncertainty in measured elemental composition and volatility resolution.