呼吸道传染疾病（如COVID-19）可在人群中快速传播。城市化的快速发展使得城市通风变差，为疾病传播创造了有利条件。呼出飞沫是呼吸道传染疾病病毒的重要载体，携有病毒的飞沫在蒸发扩散过程中可以进入到周围人群肺部造成感染，但公园空旷区域与街谷内相关暴露过程及暴露风险评估仍需进一步研究。本项目首先通过外场实验与计算流体力学（CFD）模拟，探索公园与街谷内飞沫蒸发和飞沫核形成过程及扩散过程；其次，公园空旷区域以及街谷内飞沫人际间暴露风险，着重分析建筑形态、气象条件、人际间相对位置等对飞沫在人际间浓度及粒径分布的影响；最终建立建筑形态、气象条件、人际间相对位置等与不同人群肺部暴露剂量的响应关系。相关影响机理的研究将回答：典型室外环境与气象条件下人际间的安全距离是多少？距离的增大飞沫暴露风险如何减小？若戴口罩或调整人体站位（例如交错型，避免面对面）有何改善效果？项目具有重要的科学意义。

Respiratory infectious diseases (such as covid-19) can spread rapidly among people. The rapid development of urbanization makes urban ventilation worse, which creates favorable conditions for disease transmission. Exhaled droplets are important carriers of respiratory infectious diseases. During the process of evaporation and diffusion, the droplets carrying viruses can enter the lungs of surrounding people and cause infection. However, the related exposure process and risk assessment of the park open area and the street canyon still need further study. Firstly, this project explores the evaporation and nucleation process and diffusion process of droplets in the park and street canyon. Secondly, the risk of interpersonal exposure of droplets in the open area of park and street canyon is analyzed, focusing on the impact of building shape, meteorological conditions, interpersonal relative position on the concentration and particle size distribution of droplets between people. Finally, we establish the response relationship between the lung exposure dose of different people and the building shape, meteorological conditions, relative positions of people. The research on the relevant impact mechanism will answer: what is the safe distance between people in typical outdoor environment and meteorological conditions? how to reduce the risk of droplet exposure with the increase of distance? what is the improvement if you wear a mask or adjust your body position (such as staggered type, avoid face-to-face)? The project has important scientific significance.