Eddy-covariance measurements of nitrous oxide fluxes above a city

Direct measurements of urban N2O emissions were made for the first time using the eddy-covariance technique from a tower, approximately 65 m above the street level of Edinburgh (Scotland, UK) during November 2005. The measured N2O concentrations had a median value of 358 ppbV and the overall mean measured flux was 91 ng N2O-N m−2 s−1, proving that the urban area was a significant net source of N2O for the period in question. The fluxes of N2O showed a diurnal cycle following the dynamics of the boundary layer mixing, and presenting good agreement with the traffic counts data. Emission ratios of the fluxes of N2O and the anthropogenic markers CO2 and CO were derived from the measurements, which showed for N2O/CO2 a value of 0.00025 and for N2O/CO a value of 0.011. These results show a good agreement with the NAEI implied emission ratio for urban sources and vehicular traffic.