AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Enhanced Thermal/Optical Characterization of Aerosol Elemental, Molecular, and Optical Properties
XIAOLIANG WANG, Xufei Yang, Benjamin Sumlin, Gustavo Riggio, Jerome Robles, L.-W. Antony Chen, LaxmiNarasimha Yatavelli, Judith Chow, John Watson, Desert Research Institute
Abstract Number: 384 Working Group: Instrumentation and Methods
Abstract Thermal/optical analyses are widely used to quantify organic and elemental carbon (OC and EC, respectively). This paper presents enhancement to the thermal/optical analysis to characterize aerosol elemental, molecular, and optical properties. Such multi-dimensional analysis provides a new tool to study aerosol source and impact. In the enhanced thermal/optical analyzer, a ~0.5 cm2 punch from a quartz-fiber filter sample is heated in programmed heating steps. Carbonaceous and other materials are volatilized, pyrolyzed, and combusted to gas phase compounds under either an inert ultrapure helium (He) atmosphere at lower temperatures (<= 580 °C) or a mixture of 98% He and 2% O2 atmosphere at higher temperatures (>=580 °C). For analysis of elements of C, H, N, and S, the evolved gaseous species are oxidized in a high temperature (~900 °C) CHNS reactor containing oxidizing agents to convert organic components to CO2, H2O, NOx/N2, and SO2. The oxidation products are measured by a quadrupole mass selective detector (MSD). A stream of evolved gas is sent to an O reactor consisting of a nickel-coated carbon reactant that converts O to CO. CO is then oxidized to CO2 and quantified by a nondispersive infrared (NDIR) sensor. To analyze the mass spectral fingerprints of aerosols, a stream of the evolved gas is sent through an empty quartz tube heated to 650ºC to break low-volatility, large organic molecules into small fragments, which are then analyzed by the MSD. Seven lasers in the wavelength range of 405 nm - 980 nm are used to monitor the optical reflectance and transmittance signals. The spectral signals allow estimation of brown and black carbon, provide insight into the charring process, and improve the charring correction. CHNSO abundance, mass spectra, and optical signature of model compounds and typical source and ambient aerosols will be presented.