TY - JOUR

T1 - Effects of Unstable Stratification on Ventilation in Hong Kong

AU - Gronemeier, Tobias

AU - Raasch, Siegfried

AU - Ng, Edward

N1 - Funding Information: Acknowledgments: The authors thank Weiwen Wang, School of Architecture, Chinese University of Hong Kong, for providing the building data. The study was supported by a research grant (14408214) from General Research Fund of Hong Kong Research Grants Council (HK RGC-GRF). Tobias Gronemeier was supported by MOSAIK, which is funded by the German Federal Ministry of Education and Research (BMBF) under grant 01LP1601A within the framework of Research for Sustainable Development (FONA; http://www.fona.de). The simulations were performed with resources provided by the North-German Supercomputing Alliance (HLRN). NCL (The NCAR Command Language, Version 6.1.2, 2013 (Software), Boulder, Colorado: UCAR/NCAR/CISL/VETS, http://dx.doi.org/10.5065/D6WD3XH5) was used for data analysis and visualization. The PALM code can be accessed under https://palm.muk.uni-hannover.de. The publication of this article was funded by the Open Access fund of Leibniz Universität Hannover.

PY - 2017/9/8

Y1 - 2017/9/8

N2 - Ventilation in cities is crucial for thewell being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs.

AB - Ventilation in cities is crucial for thewell being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs.

KW - Convective boundary layer

KW - LES (large-eddy simulations)

KW - Street-level ventilation

UR - http://www.scopus.com/inward/record.url?scp=85029848911&partnerID=8YFLogxK

U2 - 10.3390/atmos8090168

DO - 10.3390/atmos8090168

M3 - Article

AN - SCOPUS:85029848911

VL - 8

JO - Atmosphere

JF - Atmosphere

SN - 2073-4433

IS - 9

M1 - 168

ER -