title: Automated measurement and calibration of reactive volatile halogenated organic compounds in the atmosphere.
abstract: The automated calibration and analysis of very low mixing ratios of the reactive volatile organic halocarbons CH(3)I, CHCl(3), C(2)H(5)I, 2-C(3)H(7)I, CH(2)Br(2), CH(2)ClI, CHBr(2)Cl, 1-C(3)H(7)I, CH(2)BrI, CHBr(3) and CH(2)I(2) for long term atmospheric field measurements are described. Analytes were pre-concentrated from 3 l of air onto an adsorbent trap cooled to -10 [degree]C using Peltier plates, and rapidly transferred to a gas chromatograph (GC) by resistive heating. A two stage Carboxen 1016/Carbotrap C adsorbent trap allowed good analyte recovery and rapid desorption without the need for post-desorption cryofocussing. Halocarbons were detected using a mass spectrometer (MS) in selective ion mode. Detection limits were between 0.02 and 0.12 pptv (parts per trillion by volume) for approximately hourly samples of CHCl(3), CH(3)I, C(2)H(5)I, 1-C(3)H(7)I, 2-C(3)H(7)I, CH(2)ClI, CH(2)Br(2), CHBr(2)Cl, CH(2)BrI, CHBr(3) and CH(2)I(2) with a precision of 3-8%. A novel calibration system was constructed which utilised fixed volume (50 [micro sign]l) injections of the output of thermostatted permeation tubes into a stream of nitrogen gas in order to dilute parts per million by volume (ppmv) mixing ratios into pptv. The calibration was completely automated, allowing multi-point calibrations during routine operation. The overall accuracy of the measurements is estimated to be +/-15%. The instrument was used continuously for automated atmospheric measurements during a 4-month research cruise from Germany to Antarctica, and a 6 week field campaign at Mace Head, Ireland. The results for CHCl(3) during the latter campaign were within 13% of measurements made by a GC-MS operating continuously at the site within the long term Advanced Global Atmospherics Gases Experiment.
authors.affiliation: Department of Chemistry, University of York, Heslington, York, YO10 5DD UK. djw123@york.ac.uk
authors.forename: David J
authors.initials: DJ
authors.lastname: Wevill
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Carpenter
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002138:Calibration; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006846:Hydrocarbons, Halogenated / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D006846:Hydrocarbons, Halogenated