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ACTRIS non-methane hydrocarbon intercomparison experiment in Europe to support WMO GAW and EMEP observation networks
[摘要] The performance of 18 European institutions involved in long-termnon-methane hydrocarbon (NMHC) measurements in ambient air within theframework of the Global Atmosphere Watch (GAW) and the European Monitoring andEvaluation Programme (EMEP) was assessed with respect to data qualityobjectives (DQOs) of ACTRIS (Aerosols, Clouds, and Trace gases ResearchInfraStructure Network) and GAW. Compared to previous intercomparisonstudies the DQOs define a novel approach to assess and ensure a high qualityof the measurements. Having already been adopted by GAW, the ACTRIS DQOs are demandingwith deviations to a reference value of less than 5 % and a repeatabilityof better than 2 % for NMHC mole fractions above 0.1 nmol mol−1.The participants of the intercomparison analysed two dry gas mixtures inpressurised cylinders, a 30-component NMHC mixture in nitrogen(NMHC_N2) at approximately 1 nmol mol−1 and a whole airsample (NMHC_air), following a standardised operationprocedure including zero- and calibration gas measurements. Furthermore,participants had to report details on their instruments and assess theirmeasurement uncertainties.The NMHCs were analysed either by gas chromatography–flame ionisationdetection (GC-FID) or by gas chromatography–mass spectrometry (GC-MS). Forthe NMHC_N2 measurements, 62 % of the reported valueswere within the 5 % deviation class corresponding to the ACTRIS DQOs. ForNMHC_air, generally more frequent and larger deviations tothe assigned values were observed, with 50 % of the reported values withinthe 5 % deviation class. Important contributors to the poorer performancein NMHC_air compared to NMHC_N2 were amore complex matrix and a larger span of NMHC mole fractions (0.03–2.5 nmol mol−1).The performance of the participating laboratories were affectedby the different measurement procedures such as the usage of a two-step vs.a one-step calibration, breakthroughs of C2–C3 hydrocarbons in thefocussing trap, blank values in zero-gas measurements (especially for thosesystems using a Nafion® Dryer), adsorptive losses of aromaticcompounds, and insufficient chromatographic separation.
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