AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Hybrid Impactor-Filter Collector Extends Semi- and Non-volatile Organic Aerosol Speciation by Thermal Desorption Aerosol Gas Chromatography (TAG)
NATHAN KREISBERG, Yunliang Zhao, Chris Ruehl, Allen H. Goldstein, Susanne Hering, Aerosol Dynamics Inc.
Abstract Number: 490 Working Group: Instrumentation and Methods
Abstract Interest in intermediate volatility and semi-volatile (I/SVOC) organic compounds has increased because of their role in secondary aerosol formation. Traditionally, organic speciation is performed using a combination of filters and adsorbents to collect the particle and gas phases. The in-situ, semi-continuous thermal desorption aerosol gas chromatograph (TAG) targets particulates using inertial impaction inside a thermal desorption cell in conjunction with GC/MS analysis. By design, the TAG does not efficiently collect semi-volatiles, therefore, a thermally desorbable, all-metal-filter collector targeting low polarity I/SVOCs was developed (see Zhao et al. this conference). The thermal desorption and transfer efficiency of this new filter cell is excellent for I/SVOCs but performs less well in recovering non-volatile organic compounds as compared to the impactor cell. Although minimized by passivation techniques, irreversible sorption of non-volatile organics to a surface contributes to sample loss in thermal desorption systems. The inherently larger surface area of the filter cell relative to the original impactor cell is largely believed to explain the difference in sample recovery of the least volatile species. To extend the range of recoverable species by the filter cell, a pre-impactor stage was designed to be coupled directly to the inlet of the new cell to impact particles onto its throat, thereby closely matching the collector geometry of the original impactor cell. Size dependent particle measurements of the isolated pre-impactor stage show comparable collection efficiency to the original 9-jet impactor cell. Increased sample recovery of non-volatiles relative to the non-hybrid cell is tested using ambient measurements, and the effect of vapor collection at reduced pressure is considered. A pair of matched filter cells – one with the pre-impactor and one without – is used to measure sample recovery differences for simultaneous parallel sampling of Berkeley, CA aerosols followed by staggered GC/MS analysis.