Spatial variability of fine particle number concentration in an urban area: The effect of aspect ratio and vehicular traffic

The condensation particle number counting (CPC) technique was used to measure the number concentration of fine particles (FPs) from 20 to 1000 nm in several monitoring campaigns inside an urban area, with the aim of studying the spatial variability inside the urban area at pedestrian level and its correlation with aspect ratio H/W (height of buildings/street width) and local traffic. The effect of aspect ratio on the FP concentrations was studied in the range of 0 ≤ H/W ≤ 4.04. To study the effect of local traffic on FP concentrations, measurements were carried out in adjacent and with similar geometrics (building height, street width, and aspect ratio) pedestrian and traffic-streets. Vertical profiles were also studied measuring FP concentration in a deep street canyon at heights from 1 to 12 m. The study shows a significant impact of local traffic on FP concentrations (traffic streets 2.7 times higher than pedestrian streets). With the increase of the value of the aspect ratio, FP concentrations exceed European averages. Additionally, It was observed a clear decrease in FP concentrations with height in deep street canyons. These results emphasize the importance of aspect ratio and local traffic when assessing the impact of FPs pollution.