With the rapid growth of populations worldwide, air quality has become an increasingly important issue related to the health and safety of city inhabitants. There are quite a few factors that contribute to urban air pollution; the majority of studies examining the issue are concerned with environmental conditions, building geometries, source characteristics and other factors and have used a variety of approaches, from theoretical modelling to experimental measurements and numerical simulations. Among the environmental conditions, solar-radiation-induced buoyancy plays an important role in realistic conditions. The thermal conditions of the ground and building façades directly affect the wind field and pollutant dispersion patterns in the microclimate. The coupling effect of wind and buoyancy on the urban environment are currently hot and attractive research topics. Extensive studies have been devoted to this field, some focused on the street canyon scale, and have found that thermal effects do not significantly affect the main airflow structure in the interior of the street canyon but strongly affect the wind velocity and pollutant concentration at the pedestrian level. Others revealed that the pollutant dispersion routes can be obviously different under various Richardson numbers at the scale of the isolated building. The purpose of this review is therefore to systematically articulate the approaches and research outcomes under the combined effect of wind and buoyancy from the street canyon scale to an isolated building, which should provide some insights into future modelling directions in environmental studies.

Leakage of hazardous chemical gases during storage or transport via roadways is a common type of accident that threatens human life. This study built a typical residential building model in rural areas of southern China based on Building Information Model technology. The model was then simplified and employed as a target building to simulate the hazardous gas dispersion around it after a leak accident by means of Computational Fluid Dynamic methods. A dose-response model was combined with a probit function analysis to quantitatively identify the exposure risks for different scenarios. The impacts of source location and ventilation path on the dispersion characteristics were analyzed through comparisons of indoor concentration distributions. In addition, the study also quantified the relationship between individual mortality risk and the source intensity by employing H₂S as a source of toxic substances. If the source strength was increased by 2.5 times for the same ventilation path, the corresponding mortality rates can improve from 0.1 to 99%. The findings provide effective information about rapid consequence evaluation after accidental leakage of hazardous chemical gas and could be helpful in proposing effective emergency measures to minimize the exposure risk in roadside buildings.