资源环境科技发展态势分析平台

Four years of summertime paired urban-rural meteorological and radon observations in central Poland are used to assess the relationship between atmospheric stability and urban-induced changes to the radiation balance and surface energy budget. An existing radon-based technique for nocturnal stability classification is improved and extended to also infer daytime mixing conditions. The radon-based scheme is shown to provide a simple, effective, objective means of investigating urban energy budget closure over a range of meteorological conditions, which promises to improve estimates of energy storage and loss terms associated with urban canopies. Special attention is paid to quantifying atmospheric characteristics associated with the arbitrarily assigned radon-derived stability categories in terms of the more conventional measures: bulk Richardson number and the Monin-Obukhov stability parameter (z/L). The bulk Richardson number approach is demonstrated to be less effective at grouping periods of similar mean stability, and less selective of extremely stable conditions, than the radon-based technique. A simple box model is used in conjunction with radon observations and an assumed source function of 15 mBqm(-2)s(-1), to show that nocturnal effective mixing heights were deeper and less variable over the urban region. On stable nights hourly median effective mixing heights were 15-20m over the rural region compared to 40-45m over the urban region.

Plain Language Summary Since the global population is rising, and more people are living in cities, we need a better understanding of how cities are changing their climate and air quality to guide more efficient and sustainable urban planning. The way in which a city exchanges heat, water, and pollution with the surrounding atmosphere depends very much on prevailing weather conditions (e.g., wind, cloudiness, and rainfall) and their controls of atmospheric mixing. Separating weather-related from design-related influences on how the urban surface absorbs and redistributes energy is key to developing mitigation measures and improving urban canopy modeling. Until now, understanding weather-related controls on atmospheric mixing has required complex analyses of many and varied observations. Here we demonstrate that a superior classification of atmospheric mixing states can be achieved through a single, simple measurement of a naturally occurring gas (radon-222). This has enabled improved characterization of energy and water exchange between urban regions and their environment. This approach can be readily applied to assess the efficacy of mitigation measures of urban climate effects and to produce computational model evaluation data sets that are tailored to specific atmospheric mixing conditions. It can be applied in a similar way to investigate controls on concentration variability of urban pollutants.