Atmospheric Analysis: Gas Chromatography

The determination of both naturally produced and anthropogenic organic species in the atmosphere is a key area in atmospheric chemistry research. Nearest to the earth’s surface, within the boundary layer of the troposphere, the determination of hydrocarbon species is important because of their ability to react rapidly with NOx in the presence of sunlight to form photochemical smog. At the other extreme of the atmosphere in the stratosphere, remote measurements of very long-lived halogenated species are required because of their critical impact on ozone destruction. Species such as methane, present throughout the atmosphere, have importance as greenhouse gases and inSuence global climate and temperature change. The wide range of both shortand long-lived species that are of interest in atmospheric science coupled to extremely low concentrations and a requirement often for in situ automated analysis has led to the development of many novel chromatographic techniques and methodologies. While some atmospheric species such as organic acids, peroxides and aldehydes have been determined using high performance liquid chromatography, the majority of species are analysed using capillary gas chromatography.The range of compounds that are of interest has resulted in almost every kind of detector Rnding a role within atmospheric analysis. This article only deals with the analysis of species found in the gas phase, althoughmany species present in the atmosphere are bound to particles or are in aerosol form. A vast number of methodologies for analysis of these species exist, although in common with gas phase species, gas chromatography plays a vital role in their analysis. The range of techniques that are in use is so broad that a complete review of analytical methods is impractical. Many individual methods, however, have common components or key procedural steps and these will be discussed. A general outline of a typical atmospheric determination can be broken down into the following steps: sample acquisition, preparation, separation and detection. The Rrst two stages, acquisition and preparation, often prove to be the most challenging. A number of chromatograms obtained from atmospheric analysis are also presented in Figures 1+4. Figures 1 and 2 were obtained from an urban environment and Figures 3 and 4 came from a single Reld campaign held on the west coast of Ireland to study clean marine air.