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The emission of the tropospheric trace gas acetaldehyde was morning after the light was turned on again. This pattern determined in leaves of 4-month-old poplar trees (Populus significantly correlated with diurnal rhythms of stomatal conductance, photosynthesis, transpiration and with the concen-tremula ×P. alba) grown under controlled environmental contrations of ethanol, the assumed precursor of acetaldehyde, in ditions in a greenhouse. Using a dynamic cuvette system the xylem sap of flooded poplar trees. It may be concluded together with a high sensitivity laser-based photoacoustic dethat under conditions of diminished stomatal conductance, tection unit, rates of acetaldehyde emission were measured acetaldehyde emission declines because its diffusive flux is with the high time resolution of about 15 min. Submergence of the roots resulted in the emission of acetaldehyde by the reduced. Alternatively, reduced transpiration may decrease leaves. The emission increased linearly before reaching more ethanol transport from the roots to the shoots and appreciable amounts of the acetaldehyde precursor ethanol are lacking in or less steady-state values (ca 350 nmol m − 2 min − 1 ; ca 470 ng g − 1 dry weight min − 1 ) after approximately 6 h. Prolonged the leaves. The present results support the view that acetaldeflooding of poplar trees resulted in a clear diurnal rhythm of hyde emitted by the leaves of plants is derived from ethanol produced by alcoholic fermentation in submerged roots and acetaldehyde emission. The emission rates decreased when the transported to the leaves with the transpiration stream.

Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was operated at liquid nitrogen temperature near lambda = 5.2 microns. In the first configuration, a 100 m optical path length multi-pass cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy (CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb when using CES. The two techniques are compared, and potential future developments are discussed.

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