The spatial and temporal variations of roadside Particle Number Count [PNC] concentration have been continuously monitored around a congested urban traffic signal controlled junction intersection in Headingley, City of  Leeds, UK. The experimental work was conducted at the semi-permanently installed ‘Instrumented Junction’ research site in Headingley Leeds. Instrumentation includes: traffic flow and speed sensors (Golden River M660), above roof-top and in-street air-flows (Gill Wind Master 10 Hz sonic anemometers) four air quality stations measuring ultra-fine PNC  (TSI 3775 CPCs). One of these stations is a local urban background site. Analysis demonstrates significant variations in [PNC] between the stations, largely influenced by the prevailing winds, building geometries, background concentrations, but also tidal traffic flows. There is strong evidence of along canyon flow channelling at the sites located in irregular street canyon environments, with flows commonly parallel to the street axis. Across-canyon air-flows were also observed, which led to elevated concentrations on the  leeward side of the  canyon.