TY - JOUR

T1 - Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation - Urban Planning Perspective

AU - Kurppa, Mona

AU - Hellsten, Antti

AU - Auvinen, Mikko

AU - Raasch, Siegfried

AU - Vesala, Timo

AU - Järvi, Leena

N1 - Funding information: This study was commissioned and funded by the City Planning Department (current Urban Environment Division) of the City of Helsinki. We also acknowledge the Doctoral Programme in Atmospheric Sciences (ATM-DP, University of Helsinki), Helsinki Metropolitan Region Urban Research Program and the Academy of Finland (181255, 277664) for financial support.. Acknowledgments: This study was commissioned and funded by the City Planning Department (current Urban Environment Division) of the City of Helsinki. We also acknowledge the Doctoral Programme in Atmospheric Sciences (ATM-DP, University of Helsinki), Helsinki Metropolitan Region Urban Research Program and the Academy of Finland (181255, 277664) for financial support.

PY - 2018/2/13

Y1 - 2018/2/13

N2 - Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard. A large-eddy simulation (LES) model PALM is employed over a highly detailed representation of the urban domain including street trees and forested areas. Air pollutants are represented by massless and passive particles (non-reactive gases), which are released with traffic-related emission rates. High-resolution simulations for four different city-block-structures are conducted over a 8.2 km2 domain under two contrasting inflow conditions with neutral and stable atmospheric stratification corresponding the general and wintry meteorological conditions. Variation in building height together with multiple cross streets along the boulevard improves ventilation, resulting in 7-9% lower mean concentrations at pedestrian level. The impact of smaller scale variability in building shape was negligible. Street trees further complicate the flow and dispersion. Notwithstanding the surface roughness, atmospheric stability controls the concentration levels with higher values under stably stratified inflow. Little traffic emissions are transported to courtyards. The results provide urban planners direct information to reduce air pollution by proper structural layout of perimeter blocks.

AB - Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard. A large-eddy simulation (LES) model PALM is employed over a highly detailed representation of the urban domain including street trees and forested areas. Air pollutants are represented by massless and passive particles (non-reactive gases), which are released with traffic-related emission rates. High-resolution simulations for four different city-block-structures are conducted over a 8.2 km2 domain under two contrasting inflow conditions with neutral and stable atmospheric stratification corresponding the general and wintry meteorological conditions. Variation in building height together with multiple cross streets along the boulevard improves ventilation, resulting in 7-9% lower mean concentrations at pedestrian level. The impact of smaller scale variability in building shape was negligible. Street trees further complicate the flow and dispersion. Notwithstanding the surface roughness, atmospheric stability controls the concentration levels with higher values under stably stratified inflow. Little traffic emissions are transported to courtyards. The results provide urban planners direct information to reduce air pollution by proper structural layout of perimeter blocks.

KW - Air quality

KW - Dispersion

KW - LES

KW - Urban planning

KW - Ventilation

UR - http://www.scopus.com/inward/record.url?scp=85042231898&partnerID=8YFLogxK

U2 - 10.3390/atmos9020065

DO - 10.3390/atmos9020065

M3 - Article

AN - SCOPUS:85042231898

VL - 9

JO - Atmosphere

JF - Atmosphere

SN - 2073-4433

IS - 2

M1 - 65

ER -