Abstract View
Development and Performance Evaluation of “Chemspot” Instrument for the Characterization of Organic Aerosol
PURUSHOTTAM KUMAR, James Hurley, Nathan Kreisberg, Braden Stump, Susanne Hering, Pat Keady, Gabriel Isaacman-VanWertz, Virginia Tech
Abstract Number: 412
Working Group: Instrumentation and Methods
Abstract
Online 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, which necessarily relies on economical alternatives that can be readily operated autonomously, generally provides very limited chemical information of particulate matter. In particular, these instruments lack information on the degree of oxygenation of particles, a critical parameter in understanding the transformations and impacts of organic aerosols.
We present here the development of an aerosol chemical composition monitor (“Chemspot”) to measure aerosol mass, volatility, and elemental ratios (O:C, S:C) in a way that maximizes reliability and autonomous operation at moderate cost. Gas Chromatographic (GC) detectors including a Flame Ionization Detector (FID) and Flame Photometric Detector (FPD) are combined with a CO2 monitor to measure aerosol organic carbon, oxygen-to-carbon ratios, and total inorganic and organic sulfur. Automated calibration can be performed using a very small number of gas-phase calibrants (e.g. CO2, CH4, SF6) due to the usage of common and well-understood GC detectors. Particles are sampled by impaction onto a ~1 mm spot in a custom passivated quartz cell after passing through a condensational growth tube. The collected aerosol sample is thermally desorbed in a few controlled rapid temperature steps (for volatility binned composition) and the vaporized sample is passed through different detectors. We demonstrate here the efficient collection of particles between 10 nm and 1000 nm in diameter. Subsequent rapid thermal desorption at rates of 20 oC/s is shown to provide separation by volatility with a resolution of less than two orders of magnitude in vapor pressure. Results from the initial performance analysis of this instrument using the data obtained from organic aerosol environmental chamber experiments will be presented. Volatility-resolved carbon, oxygen, and sulfur concentrations in ambient aerosol will also be discussed.