* Air Pollution, Climate Change and Ozone Depletion  Notes

Box 4 Factors Affecting Exposure to Primary Pollutants–Wind Speed, Wind Direction and Building Geometry

Figure 5. a schematic diagram adapted from Dabbert showing how a vortex can form in a street with an aspect ratio R (height of building divided by width of street) of greater than 0.7

Material at ground level is swept from the windward to the leeward side.



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Figure 6. measurements of CO at the Marylebone Road on May 15th 2003

The red line shows data from the south side of the street (S), the dark blue line shows data from the island in the middle of the road (C) and the lighter blue line shows data from the north side of the road (N), all measurements are made simultaneously 3 m above the ground. Early in the day there were light winds and pollutant levels were similar across the street, however, the wind picked up in the afternoon and began to blow perpendicular to the road from south to north at roof level, setting up a vortex in the ‘street canyon’. A dramatic decline in CO measured at the north side of the road is mirrored by a large increase in CO measured on the south side as material is blown from north to south at ground level (data from Dr. James Tate University of Leeds as part of the DAPPLE project, www.dapple.org.uk).

 Fig. 6

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