Slemr, J*; Slemr, F*; Partridge, R H; D'Souza, H; Schmidbauer, N* (2002) Accurate measurements of hydrocarbons in the atmosphere (AMOHA): three European intercomparisons. J. Geophys. Res., 107 (D19). ACH 15-1 - 15-25

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Abstract

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 C2 to C9 non-methane hydrocarbons (NMHCs) in ambient air. Four international intercomparisons of increasing complexity were carried out over a period of four years. These were designed to evaluate the analytical performance of a considerable number of European laboratories making frequent ambient NMHC measurements, to identify the major problems encountered in these analyses and to recommend solutions for these problems. Calibration gas standards prepared gravimetrically and certified by the National Physical Laboratory (NPL) in the UK were used in all of the intercomparisons to eliminate the variability that would have been introduced by laboratories using their own calibration gas mixtures. The results presented here are for the first three of the AMOHA intercomparisons. A 4-component synthetic test gas mixture was used for the 1st intercomparison, a 30-component synthetic test gas mixture for the 2nd intercomparison, and both a pressurised ambient air sample and a 30-component synthetic gas test mixture for the 3rd intercomparison. The results of the 12 to 14 participating laboratories showed generally good agreement between their measurements and the gravimetric concentrations of the synthetic NMHC mixtures, and there was also generally good agreement between the laboratories analysing the real air samples. Most importantly, there were distinct improvements in the measurement quality achieved in this project when compared to previous European intercomparisons. This emphasised the importance of using high-quality NMHC multicomponent gas calibration standards when making accurate measurements of NMHCs in air.
The most frequent causes of problems in the chromatographic concentration measurements were found to be interference by co-elution with other compounds, breakthrough of C2 and C3 compounds during sample preconcentration, and adsorptive losses of C7 to C9 compounds in the transfer lines before the analytical instrumentation. Calibration by multicomponent NMHC standards was demonstrated to provide more accurate results, compared to the frequently used calibration with only one hydrocarbon species, such as n-butane.

Item Type:	Article
Subjects:	Analytical Science
Last Modified:	02 Feb 2018 13:17
URI:	https://eprintspublications.npl.co.uk/id/eprint/2451