Closed-path tuneable diode laser absorption spectroscopy applications

Closed-path tuneable diode laser absorption spectroscopy applications 

The effects that numerous trace gases have on our atmosphere, and associated with it our climate, have been studied extensively. Probably the most prominent of these are the greenhouse gas CO2 and O3-destroying chlorofluorocarbons (CFCs). But other trace gases associated with the two aforementioned effects also receive high attention, namely CH4 and nitrogen oxides. 

Nitrogen oxides play an important role in the photochemistry of the troposphere, controlling the formation of tropospheric O3, affecting the concentration of the hydroxyl radical, and contributing to acid precipitation. Nitrogen dioxide (NO2) is one of the most important reactive nitrogen species its photolysis is the primary source of O3 in the troposphere (see Section 28.6 for further details on the actual chemical processes and rates). 

A key issue in the research of our ecosystem and in atmospheric studies today is the ability to quantify even small concentrations of trace gases, and follow their evolution from a source to their final destination. For biosphere-atmosphere or air-sea exchange, trace gas flux measurements based on the eddy correlation technique in addition to high temporal resolution (sometimes less than 1 s) is required. Of the many 

Werle and Kormann (2001) report on a field campaign of CBU-emission measurements from rice paddy fields, simultaneously recording eddy correlation and closed-chamber data (the former by using a TDLAS system, the latter being based on the standard diffusion-chamber method). Simultaneously with the CEU-emission data, micrometeorological measurements were performed (e.g. recording wind direction and speed using a sonic anemometer). 

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