Application of a Fourier transform IR system for measurements of N₂O fluxes using micrometeorological methods, an ultralarge chamber system, and conventional field chambers

Abstract

Measurements of the sources and sinks of biogenic trace gases such as N2O and CH4 from terrestrial ecosystems are important in explaining and predicting the influence of these gases on global warming. Because of their biological origins the fluxes of these gases often show high spatial and temporal variation. Traditional methods of flux measurement use different types of field chambers or micrometeorologically based methods. These methods have several shortcomings and may not always be applicable to flux measurements of trace gases such as N2O or CH4. Fourier transform infrared (FTIR) spectroscopy, due to its path‐integrating and multicomponent nature, shows unique potential for the measurement of fluxes of greenhouse gases from various ecosystems. To assess this potential, we have used a medium resolution (1 cm−1) FTIR spectrometer to test its suitability for area‐integrated measurements, simultaneous multicomponent measurements, and continuous real‐time measurements of trace gas fluxes. We have tested three different configurations: a conventional field chamber where the FTIR is used to continuously and simultaneously monitor the concentration changes of several gases, a megachamber method using a large tent as field chamber with the FTIR optical path within the chamber, and a micrometeorological flux gradient method. The three configurations are described and discussed and their performance is demonstrated in measurements of fluxes of N2O from a fertilized grassland and CH4 from a forest soil.

Nitrogen losses following application of pig slurry to arable land

“…The closed White cell used had a volume of 25 litres, a length of 1.5 m and an optical path length of 96 m (Infrared Analysis, Supercell 100). The FTIR (Bomem MB100) was connected to the White cell to determine the build-up of N 2 O, as in Galle et al (1994) and Griffith & Galle (1998) (Fig. 1).…”

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

“…A possible larger-scale measurement technique of this sort is the time-dependent accumulation of trace gases in a measuring tunnel with open-path optical methods like FTIR (Fourier Transform InfraRed spectrometry), DOAS (Differential Optical Absorption Spectroscopy) or TDLAS (Tuneable Diode Laser Absorption Spectroscopy) along the longitudinal tunnel axis, which yields path-integrated concentration (PIC) values (see e.g. Galle et al, 1994;Schäfer et al, 2012). Measurements of fluxes at larger spatial scales (10 000 m 2 ) require the application of micro-meteorological methods (Smith et al, 1994).…”

Ammonia: Measurement Issues

“…Very large chambers have been constructed of light-weight plastic. One of these systems (Galle et al, 1994) enclosed an area of 64 m 2 and used a long-path Fourier Transform Infrared (FTIR) Spectrometer to measure changes in the concentrations of CH 4 and N 2 O. Another system (M. Poach and P. Hunt, 2001, personal correspondence) was used to cover the width of a constructed wetland for processing animal wastes.…”