We have performed a series of wind-tunnel experiments to measure scalar concentration profiles over urban-like roughness arrays. The concentration measurements revealed two features of scalar distribution. First, the high concentration filed was observed in the leeward region of each roughness element. Secondly, the averaged concentration became high up to the roughness height due to the updraft along the element and the boundary layer thickness drastically reach to the height in spite of the short length of scalar source area. In addition to the concentration measurements, we determined the roughness length of scalar based on the preliminary performed comprehensive study on scalar transfer coefficients, momentum transfer coefficients and wind profiles and discussed the similarity between momentum and scalar transfer phenomena by applying the relation between the Dalton number and the roughness Reynolds number.
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