The state of Pearl River Delta (PRD) regional air quality can be attributed to natural elements such as seasonal meteorological variability and anthropogenic factors such as pollutant emissions and physical influences exerted by urban morphology. A numerical study has been conducted to phenomenologically examine the breadth within which regional air quality can be adjusted by attenuating area-wide morphometry. Whilst urban parameterized (urbanized) mesoscale models have been successfully deployed for North American and European metropolises, this study deploys an urbanized meteorological model over a large, geographically complex mega-region, and at neighborhood scales. Differences in characteristic urban boundary layer features are evaluated for an urban fabric of high morphometric int...[ Read more ]

The state of Pearl River Delta (PRD) regional air quality can be attributed to natural elements such as seasonal meteorological variability and anthropogenic factors such as pollutant emissions and physical influences exerted by urban morphology. A numerical study has been conducted to phenomenologically examine the breadth within which regional air quality can be adjusted by attenuating area-wide morphometry. Whilst urban parameterized (urbanized) mesoscale models have been successfully deployed for North American and European metropolises, this study deploys an urbanized meteorological model over a large, geographically complex mega-region, and at neighborhood scales. Differences in characteristic urban boundary layer features are evaluated for an urban fabric of high morphometric intensity and one of reduced intensity. Consequent air quality modeling results are compared.

Firstly, formulation of the urban parameterization is introduced. Augmentations to traditional, surface layer similarity theory based formulations are highlighted. Secondly, a technique to extrapolate measured morphometry to the data-scarce PRD urban sites is shown. Then, a detail comparison of dynamical fields prognosticated for high and low urban morphometric intensities is presented. Differences in these dynamical fields are finally related to chemical transport modeling results.

The urbanized model is able to exhibit detailed vertical evolution of physical properties from the bottom of the urban canopy layer up through the atmospheric boundary layer. Wind speed decreases with greater canopy depth. The canopy top TKE shear production peak is more pronounced in deep canopies. The rate of change in TKE buoyancy production is reduced by increased canopy depth. Onset of the urban nocturnal low level jet is delayed by increased canopy depth. Unstable flow conditions reach higher altitudes over deep canopies. Strength of the nocturnal heat island is proportional to canopy depth. Due to the larger heat storage capacity in deep canopies, daytime urban heat sinks are possible.

Canopy depth causes a marked increase in urban PM₁₀ concentration near the ground and aloft. This difference is accentuated by the rate of emission - that is, concentration difference predicted between deep and shallow canopies is proportionately greater in areas of higher emission rates.