Controls on trace gas exchange observed by a conditional sampling method

The micrometeorological technique of conditional sampling has been used to measure the surface–atmosphere exchange of a number of radiatively active trace gases. This paper reviews the design and operational details of a system developed as part of the NERC TIGER programme. The system has been used to measure the exchange of carbon dioxide, methane, nitrous oxide, total hydrocarbons and nonmethane hydrocarbons. The necessary modifications to the basic system are described which permit such a wide range of compounds to be measured and typical flux estimates are given. The paper also includes some discussion of the relative sensitivity of the technique and suggests areas for future research to improve the stability and practicality of systems employing the conditional sampling approach.