The University of Leeds operates a LI-COR LI-7500 open path gas analyser. The instrument operates at infra-red wavelengths measuring the absorption due to carbon dioxide and water vapour at specific wavelengths along its 0.125m measurement path. Internally-stored calibration data are used to convert these absorption values to a mole concentration for each gas. Carbon dioxde and water vapour mole concentrations from this instrument are also combined with sonic anemomenter data at a 20Hz data acquisition rate - for example the 20 minute final fluxes product during the ASCE field campaign in summer 2014.