| Popis: |
Abstract. Annual emissions of greenhouse and other trace gases requires knowledge of the emissions throughout the year. Unfortunately emissions into the surface boundary layer during stable, calm nocturnal periods are not measureable using most micrometeorological methods due to non-stationarity and uncoupled flow. However, during nocturnal periods with very light winds the concentration of carbon dioxide (CO2) and nitrous oxide (N2O) frequently accumulates near the surface and this mass accumulation can be used to determine emissions. Gas concentrations were measured at four heights (one within and three above canopy) and turbulence was measured at three heights above a mature 2.5 m high maize canopy from 23 July to 10 September 2015. Nocturnal CO2 and N2O fluxes from the canopy were determined using the accumulation of mass within a 6.3 m vertical domain of the nocturnal surface boundary layer. Diffusive fluxes out of the top of this domain were also estimated. Fluxes during near-calm nights (friction velocities |
