CONCENTRATION FLUCTUATIONS IN URBAN CONCENTRATION FLUCTUATIONS IN URBAN STREET CANYON POLLUTANT DISPERSIONSTREET CANYON POLLUTANT DISPERSION CONCENTRATION FLUCTUATIONS IN URBAN CONCENTRATION FLUCTUATIONS IN URBAN STREET CANYON POLLUTANT DISPERSIONSTREET CANYON POLLUTANT DISPERSION

ObjectiveObjective

Pollutant concentration fluctuations are important in assessing toxic risk to people in urban street canyons. However, experimental data within typical building arrays is very limited.

BackgroundBackground

It has been suggested that the r.m.s. fluctuations (Crms) are of the order of the mean values. However, such estimates vary greatly. We aim to quantify the relationship through a lab study.

Vehicle exhaust

An urban street canyon with traffic

Research Being Carried OutResearch Being Carried Out

Various obstacle arrays have been studied in a large hydraulic flume. Concentration distribution time-histories in a series of canyons downstream of a single source have been measured using Planar Laser Induced Fluorescence (PLIF). Key FindingsKey Findings

The first data show that Crms in the shear layer above the array is of the order of the mean (Cavg). The peak of the relative intensity (Crms/Cavg) also occurs here and can exceed unity in canyons immediately downstream of the source.

Turbulentimage

Instantaneous image

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-Average image (Cavg)