The effect of water vapour broadening on methane eddy correlation flux measurements

A high resolution tunable diode laser absorption spectrometer (TDLAS) was used to measure the broadening effect of water vapor and other gases (dry air, nitrogen, oxygen, hydrogen, and helium) on three methane lines in the nu 4 fundamental. The effects on methane eddy correlation flux measurements amount to a few percent for the least broadened line for expected H2O fluxes, to about 10 percent for the most broadened line for higher H2O and lower CH4 fluxes likely to be encountered. The broadening coefficients of methane measured for air, N2, O2, and He are in good agreement with recently published values.