Monitoring CO concentration at leeward and windward sides in a deep street canyon

Carbon monoxide concentration was measured on the two sides of a deep street canyon (aspect ratio = 5.7 and width = 5.8 m). One-minute average CO concentrations were obtained during a three-day monitoring campaign using an NDIR CO spectrophotometer. Traffic flow measurements were carried out in the same period and CO emission rates in the canyon were evaluated using the COPERT procedure. Data on wind direction and intensity measured at a meteorological station few hundred meters from the monitored street canyon are reported and analyzed together with experimental data. Results show that in the street canyon the difference between the two sides of the canyon is negligible regardless of wind direction. Experimental results are confirmed by CFD simulations. This result is in contrast with those reported for street canyons with AR congruent to 1 where on the leeward and windward sides different pollutant concentrations are found when wind direction is mainly perpendicular to the street axis. Simulations carried out with a computer fluid dynamic software show that vehicle-induced turbulence plays a main role in reducing the difference of CO concentration in the two sides of the streets. Our results may be of interest for exposure studies and for developing dispersion models in deep street canyons. (C) 2008 Elsevier Ltd. All rights reserved.