Urban morphology and air quality in dense residential environments in Hong Kong. Part I: District-level analysis

The link between urban morphology and air quality in various dense residential environments of Hong Kong are investigated through field measurements and statistical analysis. With regard to the myriads of parameters available in the literature, this study aims to identify the most important urban morphological parameters in the street-level and district levels that affect air quality dispersion in Hong Kong. The study postulates that there is an association between urban morphology and urban air quality and a statistical model is developed to explain the relationship amongst urban air quality, micro-meteorology and urban morphological dimension. The study considered 20 different urban residential areas in five major districts of Hong Kong and real-time street-level air pollutant and microclimatic data are collected. 21 morphological variables are identified and calculated based on the geometry of the urban fabric. This study is the first part of a series which focuses to identify whether district demarcation is correlated with air quality. According to the findings of statistical analysis, only 6 out of 21 morphological variables (complete aspect ratio, occlusivity, roughness height, zero-plane displacement height, total building volume/number of buildings, and standard deviation of height) report distinguishable variability at the district level. Their R² (correlation coefficient) values vary from 0.2937 (plan area index) to 0.5457 (occlusivity) which is considered moderate to high. All these parameters describe the overall feature of the site rather than the specific geometric features of the street. It translates to the fact that in spite of the large in-district variations in morphological variables amongst the five districts, air pollution variations are insignificant for most of the variables and it means that air quality in Hong Kong are distinguishable not by district-level variable but rather in-site fabrics.