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Ozone precursors, odorous compounds and halogenated greenhouse gases

Environmental monitoring  ultra-volatilesMonitoring ultra-volatile compounds is an important field of environmental monitoring, as it encompasses several key classes of compounds, including:

  • Ozone precursors – Ranging in volatility from acetylene (ethyne) to trimethylbenzene, ozone precursors are believed to contribute to the formation of ground-level ozone, one of the main constituents of urban smog. Vehicle emissions are thought to be the main source of these compounds, and recent regulations require round-the-clock monitoring of key compounds to establish and monitor the link between pollution levels, traffic density, industrial emissions, and weather conditions.

  • Odorous compounds – A number of ultra-volatiles, and sulfur compounds in particular, are associated with unpleasant, pungent odours, which can be noticeable even at low concentrations. These compounds have historically been difficult to analyse, as they are ‘thermally labile’ (sensitive to high temperatures), particularly when they come into contact with metal surfaces. The detection of odorous compounds at trace levels is critically important for applications including industrial emissions testing, and the monitoring of odours from sewage treatment plants and landfill sites.

  • Halogenated greenhouse gases – In response to the Kyoto Protocol, regulations are being enacted that require the monitoring of greenhouse gases, including trace-level halogenated compounds. Some of these compounds are on the standard US EPA list of ‘air toxics’, but other compounds (some with high global warming potential) are not. These can present an analytical challenge due to their extreme volatility, and include carbon tetrafluoride, hexafluoroethane, chlorotrifluoromethane and sulfur hexafluoride.

What Markes can offer

Monitoring of ultra-volatiles typically requires on-line sampling, as most of them are too volatile to be retained on sorbent tubes at ambient temperature. Indeed, for certain ultra-volatiles thermal desorption is often the only way to provide the high degree of analyte concentration needed to address the low detection limits needed.

Many on-line thermal desorption systems are deployed remotely, or in mobile laboratories (e.g. for environmental emergency response), and use either:

  • A single focusing trap, such as the UNITY–Air Server-xr, which samples air for a defined period of time followed by analysis.

  • Two focusing traps working alternately, for continuous sampling. Systems such as the TT24-7 use wider-bore focusing traps to allow high sample loadings in short periods of time.

In either case, the use of inert flow paths is vital to ensure compatibility with highly labile analytes such as sulfur compounds.

Further information

Markes International Ltd
Gwaun Elai Medi-Science Campus
Tel: +44 (0)1443 230935
Markes International GmbH
Bieberer Straße 1-7
63065 Offenbach am Main
Tel: +49 (0)69 6681089-10
USA (West)
Markes International, Inc.
2355 Gold Meadow Way
Gold River, Sacramento
California 95670
Tel: +1 866-483-5684 (toll-free)
Markes Instruments (Shanghai) Co., Ltd
Unit 1002, Building 1
No.418, Guilin Road
Shanghai 200233
P.R. China
Tel: +86 21 5465 1216
Part of Schauenburg International

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