A case-study of fine particle concentrations and fluxes measured in a busy street canyon in Manchester, UK

Concentrations and fluxes of fine particles were measured for 2 weeks in a city centre street canyon with busy traffic. Two optical particle counters (PMS ASASP-X) were operated with ultrasonic anemometers as eddy covariance systems. One system was located at 3.5 m height between the road and pavement while the other was periodically cycled through heights of 5, 10, 15 and 18 m on a hydraulic lift. At street level, number concentrations in the range 0.1 < D(p) < 0.5 mum followed a diurnal cycle similar to that observed in other studies in the urban background, with a peak coinciding with the morning peak in traffic flow. Daytime concentrations were moderated by inverse relationships with wind speed within the canyon, as well as an independent inverse relationship with wind speed measured at a roof-top site 750 m from the canyon. The vertical turbulent flux also followed a diurnal cycle similar to that previously observed above an urban canopy, with the greatest flux occurring in the middle of the day. A negative vertical gradient in flux was typically found within the canyon. (C) 2004 Elsevier Ltd. All rights reserved.