Fast chemical sensor for eddy-correlation measurements of methane emissions from rice paddy fields

A high-frequency-modulation spectrometer with a lead-salt diode laser operating in the nu(4) band of CH(4) at 7.8 mum was used as a fast chemical sensor to measure ambient methane concentrations of 2 ppmv (parts in 10(6) volume-mixing ratio) with a time resolution of 10 Hz for micrometeorological flux measurements. To assess the quality of the data on methane emissions from rice paddy fields, we compared eddy-correlation measurements with simultaneously recorded emission data from the state-of-the-art closed-chamber technique and showed that the closed-chamber measurements were 60%-90% higher than were the eddy-correlation measurements during the campaign. This outcome demonstrates that diode-laser spectroscopy is a valuable tool for quality assurance.