Urban air pollution is becoming a more and more important environmental problem.Suitable city redevelopment is an effective way to improve urban ventilation and help pollutant dilution.This paper investigates the impact of urban open space and elevated buildings on pollutant(CO)exposure in 3-D urban canopy layer(UCL)models with medium packing density(plan area index and frontal area index □ρ=□f=0.25).Computational fluid dynamics(CFD)simulations are carried out under neutral atmospheric condition.The initial numerical UCL model consists of 5×5 cubic buildings(H=B=30m).In the first group,one of the 25 building models is removed to attain urban open space settings.In the second group,the first floor,or second floor or third floor of all building models are elevated respectively to create wind pathways through buildings.The standard k-□ model is used to model the turbulence.CFD methodologies are successfully validated by wind tunnel data.Four wind directions are considered(00,150,300,450).The contribution of pollutant concentration reduction by urban open space and elevated building is quantified by daily pollutant exposure(Et).Results show that,urban open space and elevated building can effectively reduce pollutant exposure for urban residents.Wind directions of 00 and 150 experience better pollutant dilution capacity thus attain less pollutant exposure than 300 and 450.Elevated building foundation could reduce pollutant exposure most effectively in four wind directions.