Abstract:
Concentrations and turbulent fluxes of accumulation mode particleswere measured during the 2004e2005 ‘Canopy and Aerosol Particle Interaction in Toulouse Urban Layer’ project (CAPITOUL) at the top of two intersecting street canyons and in the urban boundary layer (UBL) in Toulouse, France. Particle numbers were strongly affected by boundary layer depth and showed limited sensitivity to local emissions. Differences in the diurnal patterns of particle numberswere observed between the finer fraction (0.3e0.4 mm) and coarser fraction (1.6e2.0 mm) of accumulation mode particles, indicating different processes of formation, evolution and transportation may be dominant. Highest particle numbers were observed in the narrow street canyon which had more limited local emissions and comparatively small particle fluxes. However, the improved ventilation rate in the wider canyon was also associated with the downward mixing of particles into the street canyon fromthe UBL. The results fromthis studyclearly illustrate the temporal and spatial variability of particle numbers and fluxes in the urban atmosphere.
