H15-27: A preliminary analysis of measurements from a near-field pollutants dispersion campaign in a stratified surface layer

In order to study pollutants dispersion in a stably stratified surface layer at small scales, a pollutants dispersion field experiment program is being conducted on the site "SIRTA" in the southern suburb of Paris. The objective of the campaign is to measure at high resolution both wind turbulence and concentration of a tracer gas in a stable surface layer and in near-field. Relationships are expected between concentration fluctuations and passage of turbulent structure. In a preliminary campaign held during the winter of 2012 with continuous gas releases, we have 12 ultrasonic anemometers measuring wind velocity and temperature at 10Hz, and 6 photo-ionisation detectors measuring gas concentration at 50Hz. Turbulence is verified to be anisotropic by calculating variances, integral length scales and power spectra for the three velocity components. A-1 power law subrange has been found in velocity power spectra in a lower frequency region next to the inertial subrange. Also, we have deduced eddy advection velocity from spatial velocity cross-correlation and found it greater than mean wind speed measured directly by sensors. Concentration measurements are corrected by using a baseline method. Significant relationships between concentration and turbulence measurements at high frequency are still under further study.