Abstract:

Under the accelerated construction of urbanization, street canyons have become an important spatial component constituting the urban built environment. There are significant differences of PM₁₀ and PM_2.5 mass concentrations within street canyons, and building spatial form is an important influencing factor. This study selects Tong’an Street in Baohe District, Hefei City, Anhui Province, monitors the changes of PM_2.5 and PM₁₀ mass concentrations and evaluates their air quality, studies the spatial morphology of street canyons from a multidimensional perspective, and proposes an optimization strategies for the spatial morphology of sunken squares in street canyons. The results show that 1) the daily average mass concentrations of PM_2.5 and PM₁₀ in the street canyon show the characteristics of multi-peak variations, and the maximum values of PM_2.5 and PM₁₀ mass concentrations appear in the interval of 08:00−09:00, and the minimum values in the interval of 13:00−14:00. so it is suggested that the residents of Tongan Street choose to avoid the weekday morning peak period and travel between 13:00−16:00 in the afternoon can reduce the impact of PM_2.5 on human health. 2) AQI was used to evaluate the air quality of each monitoring point in Tong’an Street, and the results showed that the air quality condition was mainly excellent, with the grades mostly distributed in Class 1 and Class 2. The air quality of the pocket park where point E is located is the best, and the air quality of the commercial sunken square where point B is located is the worst. 3) The degree of influence of each building form design index on PM_2.5 and PM₁₀ quality concentration of street canyon is ranked from the largest to the smallest: vegetation coverage ratio>height-width ratio>building height ratio>relative elevation>building setback>Sky View Factor. Among them, vegetation coverage is significantly negatively correlated with PM_2.5 and PM₁₀ mass concentrations in the street canyon, and increasing greenery in the street setback space can significantly improve its air quality. 4) Appropriately increasing the height to width ratio of buildings and using a bottom-overhead structure can reduce the obstruction of buildings to the air flow near the ground, which is conducive to improving the air quality within street canyons. 5) The greater the settlement height of the sunken square in the street canyon, the more unfavorable the diffusion of pollutants in the site and bring negative impact on air quality, while the appropriate increase of the width of the sunken plaza is conducive to the improvement of the air quality in the site. The study aims to provide planning strategies and scientific basis for pollution mitigation in urban street canyons, and to provide reference for new and modified urban street canyon spatial forms and the development of urban traffic and travel policies.

Key words: street canyon, PM_2.5, spatial form, air quality evaluation, sunken square, numerical simulation, optimization strategy

摘要：

在城市化加速建设的情况下，街道峡谷已成为城市建成环境重要的空间组成部分。街道峡谷中PM_2.5和PM₁₀质量浓度存在显著差异，建筑空间形态是其重要的影响因素。选取安徽省合肥市包河区同安街道为研究对象，监测PM_2.5和PM₁₀质量浓度变化并对其进行空气质量评价，从多维度视角出发研究街道峡谷空间形态，并对街道峡谷中下沉广场这一特殊建筑空间形态提出优化策略。结果表明，1）街道峡谷内PM_2.5、PM₁₀的日均质量浓度均表现出多峰变化的特点，PM_2.5和PM₁₀质量浓度最大值出现在8:00－9:00区间，最小值出现在13:00－14:00区间，因此建议同安街道的居民尽量避开工作日早高峰时期，在下午13:00－16:00期间出行，以减少颗粒物对健康的危害。2）运用AQI对同安街道各监测点空气质量进行评价，结果表明其空气质量状况以优良为主，等级多分布在1级和2级。其中选点E所在的口袋公园空气质量最优，选点B所在的商业下沉广场空气质量最差。3）各个建筑空间形态设计指标对街道峡谷PM_2.5和PM₁₀质量浓度影响程度由大到小排序为：植被覆盖率>高宽比>建筑高度比>相对高程>建筑退界>天空开阔度。其中植被覆盖率与街道峡谷中的PM_2.5和PM₁₀质量浓度呈显著负相关，在街道退界空间中增加绿化可以显著改善其空气质量。4）适当提高建筑高宽比，采用底层架空以减少建筑物对近地面空气流动的阻碍作用，有利于改善街道峡谷内的空气质量。5）街道峡谷内下沉广场的高度越深，越不利于污染物在场地内的扩散，并对空气质量带来消极影响，而适当地增加下沉广场的宽度，对提高场地内的空气质量有一定作用。该文旨在为城市街道峡谷改善环境质量提供规划策略和科学依据，为城市街道峡谷空间形态优化设计和城市交通出行提供参考依据。

关键词: 街道峡谷, 颗粒物（PM_2.5）, 空间形态, 空气质量评价, 下沉广场, 数值模拟, 优化策略