城市绿化和开放空间对城市污染物扩散和热环境的定量影响

This project will first carry out some high-quality scale-model outdoor measurements by designing idealized two-dimensional (2D) street canyon and three-dimensional (3D) urban district models with the medium or high building packing densities. These models are flexible in controlling the parameters of building morphologies/urban vegetation/pollutant source settings, meanwhile can attain sufficient urban thermal inertial and satisfy the requirements of dynamic/thermal inertia similarity with respect to realistic urban area. Meanwhile, basing on the complete literature review and under the validation of experimental data, the porous medium model for thermal-dynamic effects of urban vegetations and the numerical accuracy of computational fluid dynamic (CFD) simulations will be improved with steady and unsteady atmospheric conditions. By adopting both experiments and CFD simulations, this study will quantify the impacts of typical building morphologies, urban vegetation in streets and open space on the spatial/temporal characteristics of urban turbulence and urban thermal environment, pollutant dispersion and their human exposure. Pollutant intake fraction and pollutant daily exposure will be adopted to quantify human exposure to pollutants in street canyons. The physiological equivalent temperature (PET) will be introduced to evaluate outdoor thermal comfort. By integrating the results of idealized cases with field measurements and CFD simulations in realistic urban districts with urban vegetations, the optimization design of urban vegetations will be explored which can contribute in reducing urban air pollutant exposure and urban heat island intensity, meanwhile providing scientific reference/effective methodologies for sustainable urban climate design. Various meteorological conditions include parameters of solar radiation, wind speed and directions, thermal stratification (i.e. stable, neutral and unstable), moreover three situations will be investigated, i.e. dynamic force dominating, thermal buoyancy force dominating, and both forces are significant. Two kinds of urban vegetations will be included (tree planting and shrubbery planting) with the parameters of vegetation canopy volume, leaf area density and porosity, vegetation location and height, the vegetation area of urban open space etc.

本项目拟构建热惯性足够大、建筑形态与绿化及污染源参数可控、能达到真实街区热力学相似要求的缩尺尺度中高密度理想街区模型(二维-三维)，进行高质量的外场实验。基于文献调研和实验数据，改进稳态与非稳态气象条件下街区绿化的多孔介质模型，并提高其计算流体力学模拟的准确性，两者的结合定量研究典型建筑形态、街道绿化与开放空间绿化对城市湍流与热环境时空特征、空气污染物扩散及其人群暴露的影响机理。采用污染物吸入比和日暴露量分析人群暴露程度，采用生理等效温度评价室外热舒适性，与真实街区外场观测及数值模拟配合，优化街区绿化设计以减少污染物人群暴露和降低城市夏季热岛强度，为构建可持续性城市气候提供科学依据及有效的研究方法。气象要素包括太阳辐射、风速风向和温度层结(即稳定-中性-不稳定)，并考虑风力主导、热力主导和两者共同作用；绿化参数包括树木与灌木冠层容积、叶面密度和孔隙率、高度及位置、开放空间绿化面积等。

申请人从城市几何形态和绿化影响城市微气候角度开展了较为系统的创新性研究，基于精细化观测与数值模拟探究城市通风、热环境、污染扩散机理及其优化设计，为可持续城市气候规划与预测提供了科学依据和新型有效的方法。首先，开展广州、珠海真实城区实地观测，量化城市风热环境时空特征，更重要的是创建绿化与建筑几何布局、储热项易测的缩尺尺度中高密度二维街谷和三维城区模型，弥补亚热带城市气候参数化缩尺实验空白，分析气象要素（风速风向与辐射条件）、建筑密度与高宽比、树种与绿化密度等对城市风热环境和能量平衡时空特征的影响，为城市冠层模型及数值模拟提供实验验证。其次，在实验数据的验证下，改进数值模拟的准确性，并将城市通风概念与污染物吸入比引入计算流体力学数值模拟，揭示气象要素(风速风向、太阳高度角、不同风力与热力相对重要性等)、建筑形态参数、树木绿化参数与光化学反应等对街区湍流、通风与污染暴露的动力/热力影响机理。..在项目执行过程中，项目负责人新增承担国家自然科学基金面上1项、获广东特支计划科技创新领军人才(2019)。共发表标注本项目资助的SCI论文近44篇，其中项目负责人为第一或通讯作者的SCI论文27篇(含JCR一区或影响因子IF>6.5共27篇）。项目负责人还参加国内外学术报告进行特邀报告10余次，并多次担任会议分会场主持、国际学术委员会委员等，研究生获得最佳会议论文奖4人次，研究成果获得国内外学者广泛关注与好评。执行期内项目负责人还引进中山大学副教授4名（含海外优青1名）、博士后2名，组建了一个搭配合理、有活力有凝聚力的城市气象研究团队；培养博士研究生4名毕业，硕士研究生6名毕业。