ABSTRACT
This chapter discusses how to sample the trace gases and particles correctly and how to measure their concentrations. Trace gases normally have concentrations in the parts per billion and parts per trillion ranges, and therefore require more specialist techniques and sensitive methods than those in general use for gases such as water vapour or carbon dioxide that occur at percentage or parts per million concentrations. Many air pollutant concentrations are highly variable, with a low average and a large range between near-zero minimum values and maxima during episodes. In gas chromatography, the mobile or carrier phase is a gas (commonly nitrogen, helium or argon). The task of sampling is to get a representative sample of particles from the air into the measuring device without changing the concentration or the characteristics on the way. Particles are accumulated on a filter and analysed by the full range of chemical laboratory techniques for the materials of interest.
