Abstract View
A New Moderate-cost Method for the Characterization of Organic Aerosol by Volatility and Elemental Ratios
PURUSHOTTAM KUMAR, James Hurley, Nathan Kreisberg, Braden Stump, Susanne Hering, Patricia Keady, Gabriel Isaacman-VanWertz, Virginia Tech
Abstract Number: 449
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 only measurements of particle mass and, consequently provides limited chemical information. 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 a new 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 a 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. By relying on common and well-understood GC detectors, calibration can be easily automated using only a small number of gas-phase standards. Particles are sampled by impaction into a ~1 mm spot in a custom passivated quartz cell after passing through a condensational growth tube. The collected aerosol sample is thermally desorbed at different temperatures (for volatility binned composition) and the vaporized sample is passed through different detectors. Volatility resolution is achieved through controlled rapid temperature steps. 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. Volatility-resolved carbon, oxygen, and sulfur concentrations in ambient aerosol will be presented.