Effects of building–roof cooling on the flow and dispersion of reactive pollutants in an idealized urban street canyon

Abstract This study investigated the characteristics of the flow and dispersion of reactive pollutants in three-dimensional idealized street canyons in the presence of building-roof cooling to provide implications in how a green-roof system contributes to mitigating of pedestrian exposure to near-roadway air pollution in street canyons. The pollutant chemistry was simulated using a coupled CFD-chemistry model. In the presence of building-roof cooling, winds and temperature fields inside the building canopy of the street canyon were significantly modified. Building-roof cooling, intensified the street-canyon vortex strength (up to 26.6% in downdraft, 10.4% reverse flow, and 7.7% in updraft). Building-roof cooling also decreased air temperature in the street canyon by supplying cooler air near the building roof. The changes in the in-canopy distributions of primary pollutants (NOX, VOCs and CO) due to building-roof cooling were mainly caused by the modified mean flow rather than the chemical reactions. High concentrations of primary pollutants occurred near the upwind building because the reverse flows were dominant at street level, making this area the downwind region of emission sources. Ozone concentrations were lower than the background concentration near the ground, where NOX concentrations were high. Building-roof cooling decreased primary pollutant concentrations by approximately −2.4% compared to those under non-cooling conditions. By contrast, building-roof cooling increased O3 concentrations by about 1.1% by reducing NO concentrations in the street canyon compared to concentrations under non-cooling conditions.

[1]  Helen ApSimon,et al.  A numerical study of atmospheric pollutant dispersion in different two-dimensional street canyon configurations , 2003 .

[2]  S. Murakami,et al.  Wind tunnel experiments on how thermal stratification affects flow in and above urban street canyons , 2000 .

[3]  Charles J. Weschler,et al.  Ozone’s Impact on Public Health: Contributions from Indoor Exposures to Ozone and Products of Ozone-Initiated Chemistry , 2006, Environmental health perspectives.

[4]  B. Givoni,et al.  Urban design factors influencing heat island intensity in high-rise high-density environments of Hong Kong , 2007 .

[5]  Stephan Weber,et al.  Comparative microclimate and dewfall measurements at an urban green roof versus bitumen roof , 2015 .

[6]  S. Beecham,et al.  Developing resilient green roofs in a dry climate. , 2014, The Science of the total environment.

[7]  Jong‐Jin Baik,et al.  Effects of building roof greening on air quality in street canyons , 2012 .

[8]  Yu Zhou,et al.  Trends in vehicular emissions in China's mega cities from 1995 to 2005. , 2010, Environmental pollution.

[9]  Riccardo Buccolieri,et al.  Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations – Evaluation of CFD data with experimental data , 2008 .

[10]  Weeratunge Malalasekera,et al.  An introduction to computational fluid dynamics - the finite volume method , 2007 .

[11]  D. Jacob,et al.  Global modeling of tropospheric chemistry with assimilated meteorology : Model description and evaluation , 2001 .

[12]  B. Maiheu,et al.  Impact of trees on pollutant dispersion in street canyons: A numerical study of the annual average effects in Antwerp, Belgium. , 2015, The Science of the total environment.

[13]  D. Carslaw.  Evidence of an increasing NO2/NOX emissions ratio from road traffic emissions , 2005 .

[14]  Sandrine Anquetin,et al.  Pollutant dispersion and thermal effects in urban street canyons , 1996 .

[15]  N. Wong,et al.  Investigation of thermal benefits of rooftop garden in the tropical environment , 2003 .

[16]  P. Jones,et al.  Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates , 2008 .

[17]  D. Lu,et al.  Estimation of land surface temperature-vegetation abundance relationship for urban heat island studies , 2004 .

[18]  Takashi Asaeda,et al.  Heat storage of pavement and its effect on the lower atmosphere , 1996 .

[19]  R. Kovats,et al.  Climate change and human health: impacts, vulnerability and public health. , 2006, Public health.

[20]  H. Cheong,et al.  Characteristics of flow and reactive pollutant dispersion in urban street canyons , 2015 .

[21]  Jong-Jin Baik,et al.  Effects of street-bottom and building-roof heating on flow in three-dimensional street canyons , 2010 .

[22]  Kyunghee Choi,et al.  Emission inventory of VOCs from mobile sources in a metropolitan region , 2006 .

[23]  Jong‐Jin Baik,et al.  A numerical study of the effects of ambient wind direction on flow and dispersion in urban street canyons using the RNG k–ε turbulence model , 2004 .

[24]  Oliver Wild,et al.  Fast-J: Accurate Simulation of In- and Below-Cloud Photolysis in Tropospheric Chemical Models , 2000 .

[25]  Jong-Jin Baik,et al.  A CFD modeling study of the impacts of NOx and VOC emissions on reactive pollutant dispersion in and above a street canyon , 2012 .

[26]  A. Pisello,et al.  Thermal-physics and energy performance of an innovative green roof system: The Cool-Green Roof , 2015 .

[27]  J. C. Martínez-García,et al.  Correlation between global solar irradiation and air temperature in Asturias, Spain , 2009 .

[28]  M. Santamouris,et al.  On the impact of urban climate on the energy consumption of buildings , 2001 .

[29]  J. Beringer,et al.  Assessing practical measures to reduce urban heat: Green and cool roofs , 2013 .

[30]  Jörg Franke,et al.  COST 732 in practice: the MUST model evaluation exercise , 2011 .

[31]  R. Turco,et al.  SMVGEAR: A sparse-matrix, vectorized gear code for atmospheric models , 1994 .

[32]  David D. Apsley,et al.  Flow and dispersion over topography: A comparison between numerical and laboratory data for two-dimensional flows , 1997 .

[33]  Xiaoming Cai,et al.  A study of the dispersion and transport of reactive pollutants in and above street canyons: a large eddy simulation , 2004 .

[34]  Ingegärd Eliasson,et al.  Surface heating in relation to air temperature, wind and turbulence in an urban street canyon , 2007 .

[35]  Jong-Jin Baik,et al.  Modeling reactive pollutant dispersion in an urban street canyon , 2007 .

[36]  Rokjin J. Park,et al.  Urban air quality modeling with full O3–NOx–VOC chemistry: Implications for O3 and PM air quality in a street canyon , 2012 .

[37]  Dara Entekhabi,et al.  Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation , 2012, Boundary-Layer Meteorology.

[38]  Shaodong Xie,et al.  Spatial distribution of traffic-related pollutant concentrations in street canyons , 2003 .

[39]  Jong-Jin Baik,et al.  Further studies of flow and reactive pollutant dispersion in a street canyon with bottom heating , 2008 .