title: Construction of a cryogen-free thermal desorption gas chromatographic system with off-the-shelf components for monitoring ambient volatile organic compounds.
abstract: An automated gas chromatographic system aimed at performing unattended measurements of ambient volatile organic compounds was configured and tested. By exploiting various off-the-shelf components, the thermal desorption unit was easily assembled and can be connected with any existing commercial gas chromatograph in the laboratory to minimize cost. The performance of the complete thermal desorption gas chromatographic system was assessed by analyzing a standard mixture containing 56 target nonmethane hydrocarbons from C2 -C12 at sub-ppb levels. Particular attention was given to the enrichment efficiency of the C2 compounds, such as ethane (b.p. = -88.6°C) and ethylene (b.p. = -104.2°C), due to their extremely high volatilities. Quality assurance was performed in terms of the linearity, precision and limits of detection of the target compounds. To further validate the system, field measurements of target compounds in ambient air were compared with those of a commercial total hydrocarbon analyzer and a carbon monoxide analyzer. Highly coherent results from the three instruments were observed during a two-month period of synchronized measurements. Moreover, the phenomenon of opposite diurnal variations between the biogenic isoprene and anthropogenic species was exploited to help support the field applicability of the thermal desorption gas chromatographic method.
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.|Department of Atmospheric Sciences, National Central University, Taoyuan, Taiwan.
authors.forename: Chang-Feng
authors.initials: CF
authors.lastname: Ou-Yang
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Liao
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.
authors.forename: Pei-Chieh
authors.initials: PC
authors.lastname: Wang
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.
authors.forename: Gang-Jei
authors.initials: GJ
authors.lastname: Fan
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.
authors.forename: Chien-Cheng
authors.initials: CC
authors.lastname: Hsiao
authors.affiliation: Graduate Institute of Energy Engineering, National Central University, Taoyuan, Taiwan.
authors.forename: Ming-Tung
authors.initials: MT
authors.lastname: Chuang
authors.affiliation: Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan.
authors.forename: Chih-Chung
authors.initials: CC
authors.lastname: Chang
authors.affiliation: Department of Atmospheric Sciences, National Central University, Taoyuan, Taiwan.
authors.forename: Neng-Huei
authors.initials: NH
authors.lastname: Lin
authors.affiliation: Department of Chemistry, National Central University, Taoyuan, Taiwan.
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Wang
keywords: Air quality/ Deans switch; Ethylene; Ozone precursors