Extending the analysis of ozone precursors – Continuous, unattended, cryogen-free on-line monitoring of PAMS hydrocarbons and polar VOCs in ambient air by TD–GC–MS

Summary

This Application Note describes validation of a cryogen-free thermal desorption (TD)–GC–MS system for on-line monitoring of an extended range of very volatile species in ambient air, which includes ‘ozone precursors’ (as specified by the US PAMS program), polar compounds and monoterpenes. In addition to analysis of a 61-component standard mix and a real air sample, we demonstrate low method detection limits using the new trap-based Kori-xr system for eliminating water from the air stream.

Introduction

The presence of volatile hydrocarbons in urban atmospheres is believed to contribute to the formation of ground-level ozone, one of the main constituents of urban smog. The compounds of interest range in volatility from acetylene to trimethylbenzene, and are generally referred to as ‘ozone precursors’. There is currently growing interest in carrying out continuous time-resolved measurement (‘on-line monitoring’) of ozone precursors and other compounds, for source apportionment and in order to better understand the factors that influence their concentrations. This is particularly the case in Asia, with recent strong growth in on-line monitoring of industrial emissions in China,^1,2,3 following the mandating of a nationwide real-time air monitoring system in the 13th Five-Year Plan, and numerous regional controls on industrial VOC emissions. On-line industrial air monitoring is also experiencing a high level of interest in South Korea,^4,5,6 while other areas also receiving attention include emissions from road vehicles^7,8,9 and long-range transport of pollutants.^10,11 For many years, however, the main user of technology for on-line monitoring of emissions from industrial and urban sources has been the US, through its network of Photochemical Assessment Monitoring Stations (PAMS). Since 1993, this program has required US states and local environmental agencies to measure ozone precursors in areas affected by significant ground-level ozone pollution.

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