Measurements of N2O fluxes from the city of Edinburgh

Direct measurements of urban N2O emissions were made using the eddy covariance technique from the top of a tower, approximately 65 m above the street level of Edinburgh, Scotland during the winter in 2005. A fast response ultrasonic anemometer was mounted on a 2.5-m mast fixed to the upwind edge (for the preferred westerly airflow) on top of the external wall of Nelson Monument, situated on Calton Hill, near the Edinburgh city centre. The N2O concentration was measured by a Tunable Diode Laser Absorption Spectrometer (Aerodyne Research Inc.): the system was operated at a frequency of 10 Hz, and the air sample was pulled through an inlet line to the sonic anemometer. Several chemical species were measured during the same field campaign: fluxes of size segregated aerosol, particle number and chemically speciated aerosol were measured by using respectively an Ultra-High Sensitivity Aerosol Spectrometer, a Condensation Particle Counter and an Aerosol Mass Spectrometer; fluxes of selected Volatile Organic Compounds were measured with a Proton Transfer Reaction Mass Spectrometer; CO2 fluxes by InfraRed Gas Analyser, and CO fluxes by vacuum ultraviolet absorption spectrometry. The fluxes are representative of footprint source areas of several square kilometres (see Nemitz et al., 2002). Relationships are established between the fluxes of N2O and the other pollutant species measured at the site: in particular with the anthropogenic markers CO2 and CO, to investigate the controls of the emission and provide a relative emission factor.