SET2018, Wuhan, 21

st - 23rd August 2018

On the relationship betw

een inhom

ogeneous temperature

distribution and pollutant concentration for real street canyons w

ith and without

trees using computational fluid

dynamics m

odellingBeatrice Pulvirenti 1, Federico Prandini 1,

Silvana Di Sabatino

2

1 Department of Industrial Engineering, University of Bologna, Italy

2 Department of Physics, University of Bologna, Italy

This study has been supported by iSCAPE Project(Im

proving Smart Control of Air Pollution in Europe)

which is fouded by the European Com

munity's H

2020 H

2020-SC5-04-2015 under the Grant Agreem

entN

o. 689954

SET2018 Conference21

st - 23rd 2018, W

uhan, China

Motivation

The progressive climate-changes influence

the comfort levels w

ithin the cities.W

e want to study the influence of

solar radiation and trees to the tem

perature and pollutant distribution at street-level.

SET2018, Wuhan, 21

st - 23rd August 2018

Heat island

Street canyons

Pollution

Mitigation by vegetation

Climate-changes

Influence of city morphology

and trees

SET2018, Wuhan, 21

st - 23rd August 2018

Jian Hang et al., The influence of building height variability on pollutant dispersion and pedestrian ventilation in idealized high-rise urban areas. Building and Environment, 2012

Wang X et al., Effects of street orientation on dispersion at or near urban street intersections. Journal of Wind Engineering and Industrial Aerodynamics, 2007

Buccolieri R.et al., Aerodynamic effect of treeson pollutant concentrations in street canyonsScience of the Total Environment, 2009

Thermal circulation

within street-canyon

SET2018, Wuhan, 21

st - 23rd August 2018

W/H

=2

W/H

=1

leeward heating

ground heatingw

indward heating

weak dependence on

the aspect ratio (the vortex is enhanced by the buoyancy)

vortex weaker as the

aspect ratio increases (larger vertical velocity could break the vortex at sm

aller aspect ratios)

clockwise vortex

suppressed by the anti-clockw

ise vortex as W/H

decreases

Clockwise vortex

Anti-clockwise vortex

Two street canyons and

Measurem

ent sites

SET2018, Wuhan, 21

st - 23rd August 2018

No trees

Trees

Comparison betw

een the tw

o street canyons

SET2018, Wuhan, 21

st - 23rd August 2018

Θ = 20°

H = 29 m

W =

20 mH/W

= 1.65

City center

No trees

4 lanes

Buses

Θ = 25°

H = 17m

W =

25mH/W

= 0.7

Residential

Trees

2 lanes

Cars

No treesTrees

Dom

ain chosen for CFD

SET2018, Wuhan, 21

st - 23rd August 2018

No treesTrees

mesh: 19 m

illionof unstructured parallelepipedelem

entsw

ith a high refinem

entw

ithin the canyon

trees modelled

as porous materials

with LAD (Leaf Area

Density Index) =

1.6 m2 m

-3

Velocity boundary conditions

SET2018, Wuhan, 21

st - 23rd August 2018

NO

RTH

SO

UTH

WES

TEA

ST

2.98% 5.96% 8.94% 11.9% 14.9%

WIN

D S

PEED

(m/s) >= 11.10

8.80 - 11.10

5.70 - 8.80

3.60 - 5.70

2.10 - 3.60

0.50 - 2.10

Calm

s: 0.00%

timedirection (°)

velocity (m/s at 150 m)

no trees canyon CO (g/h)

trees canyon CO (g/h)

14:00110

3,556069

2362701:00

2012,9

166778793

110°

201°Atm

ospheric Boundary Layer (ABL)

Measurem

ents fromAU

GU

ST 22nd, 12.00

(2017) to AU

GU

ST 23rd 12.00

Temperature boundary conditions:

measurem

ents by IR cameras

SET2018, Wuhan, 21

st - 23rd August 2018

No trees

Trees

S. Di Sabatino, F. Barbano, C. Barbieri, E. Brattich, A.F. Brunetti, A. Drebs, P. Kumar, K. Jylhä, E. M

inguzzi, M. Nardino, F.

Pilla, B. Pulvirenti, L. Torreggiani, A. Valmassoi, Urban Heat Island, Air Pollution and Clim

ate Change: the Bologna (IT) iSCAPE case study. AM

S Annual Meeting, Austin, Texas, 2018

SET2018, Wuhan, 21

st - 23rd August 2018

New

approach: radiation view

factors evaluation

Heat flux to the walls

Surfaces partially overlooked

CEYLING TO WALL

FLOOR TO CEYLING

SET2018, Wuhan, 21

st - 23rd August 2018

CFD results

Effect of city morphology

Effect of building facades heating

No heatingHeating

Perpendicular windParallel windCO

concentrationw

ind direction

winddirection

SET2018, Wuhan, 21

st - 23rd August 2018

CO concentration

CFD results - com

parisonbetw

een the two canyons

CO concentration

No treesTrees

Heat island effects

SET2018, Wuhan, 21

st - 23rd August 2018

~ 7 °C

~ 5 °C

~ 20km

No trees

Trees~ 3km

Trees

No trees

Conclusions

SET2018, Wuhan, 21

st - 23rd August 2018

•The pollutant concentration is affected by the urban canyon m

orphology. The m

orphology represents then a structural constraint that affects the atm

ospheric circulation and consequently the pollutant hotspots.

•In particular, near street intersections m

any hotspots are observed, for all the directions of the w

ind. Street intersections are then structural elements that

should be designed ad hoc if possible.

•The heat island effect is strong, show

ing a difference of 2-3 degrees within

short distances.

•Therm

al circulation within the urban street canyon produces higer pollutant

concentration at a street level. The presence of trees could mitigate this

effect, especially during the night.

Thank you!

This study has been supported by iSCAPE Project(Im

proving Smart Control of Air Pollution in Europe)

which is fouded by the European Com

munity's H

2020 H

2020-SC5-04-2015 under the Grant Agreem

entN

o. 689954

Aknowledgem

ents:The Authors are grateful to Francesco Barbano and Erika Brattich for their precious help in the interpretation of experim

ental resultsThe Authors are grateful to ARPAE group (Luca Torreggiani and Carla Barbieri) for their m

easurements stations

SET2018, Wuhan, 21

st - 23rd August 2018