AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Development of an In Situ Thermal Desorption Gas Chromatograph for Intermediate-Volatility and Semi-volatile Organic Compounds
YUNLIANG ZHAO, Nathan Kreisberg, Susanne Hering, Allen H. Goldstein, University of California, Berkeley
Abstract Number: 450 Working Group: Instrumentation and Methods
Abstract Intermediate-volatility and semi-volatile organic compounds (I/SVOCs) have been shown to play a significant role in the formation of secondary organic aerosol; however, the abundance and composition of I/SVOCs in the atmosphere is poorly understood partly due to the lack of instrumentation capable of in-situ measurements of these compounds. In response to this need, we have developed a new sampling inlet and a new collection and thermal desorption system for the Thermal desorption Aerosol Gas chromatography instrument (TAG) to extend its capability to speciated analysis of I/SVOCs. The new sampling inlet consists of two parallel sampling lines, a bypass line and an activated carbon denuder line. The new collection and thermal desorption system consists of a metal fiber filter collection cell and a cold trap made of a section of metal capillary column. Gases and particles are collected by the metal fiber filter with phase partitioning determined by periodic sampling through the denuder. Organics thermally desorbed from the filter are refocused onto the cold trap followed by thermal transfer into a gas chromatograph/mass spectrometer (GC/MS) for analysis. Extensive laboratory tests were made to develop the operating method and to evaluate the performance of these new components. Results demonstrate that the combination of the new collection and thermal desorption system and GC/MS is able to quantitatively measure organic compounds with vapor pressures lower than n-tetradecane (C14). The revised instrument was used to measure speciated I/SVOCs in Berkeley, CA in a fully automated, continuous mode of operation. These measurements not only provide the direct examination of gas/particle partitioning of organic compounds, but also provide source markers for gas-phase organics that serve to constrain the abundance of primary I/SVOCs in the atmosphere. Additionally, these measurements show that many of the organic markers for organic aerosol are actually present as SVOCs.