European hydrocarbon intercomparison experiment AMOHA part 4: Canister sampling of ambient air

摘要

The AMOHA (Accurate Measurements of Hydrocarbons in the Atmosphere) project was proposed to evaluate and improve current gas chromatographic methods used across Europe to determine concentrations of nonmethane hydrocarbons (NMHCs) in ambient air. This paper presents results of the final task of AMOHA (4th intercomparison) whose major objective was to test the overall analysis performance of the participating laboratories. The 4th intercomparison, which included both the sampling procedure and storage in stainless steel canisters, was carried out in two phases. In the first phase, canisters used by nine participating laboratories and reference canisters by the Norwegian Institute for Air Research (NILU) were filled at NILU with a compressed air test sample containing hydrocarbons with mixing ratios between 13 pptv (parts per trillion by volume) and 3400 pptv. The canister samples were analyzed immediately by NILU, and then the participants analyzed their own three canisters and one canister from NILU. All analyses considered 28 C2–C8 compounds. The results were based on a gravimetric standard mixture by the National Physical Laboratory (NPL). The hydrocarbon composition in the participants' canisters was generally found to be stable for storage periods of several weeks, except for three canister sets showing substantial deviations from the corresponding reference concentrations by NILU. Discrepancies between the participants' analyses and the reference concentrations were mostly due to analytical uncertainties of the respective laboratory. In the second phase, 11 participating laboratories collected ambient air samples using their own sampling equipment and canisters at the Meteorological Observatory Hohenpeissenberg. The sampling was synchronized with an on-line NMHC instrument. The air samples were cleaner than during the first phase, with more than 60% of the analyzed compounds below 100 pptv. Generally, the medians of canister analyses were in good agreement with concurrent on-line measurements, although the concentrations of alkenes and aromatic compounds found by several participants were higher than those measured on-line. The performance of the participating laboratories differed considerably, and six out of eleven participating laboratories achieved good agreement to the reference values for most compounds.