## 1 Introduction
In recent years, computational fluid dynamics (CFD) technology has been gradually applied to the study of pollutant dispersion around buildings. In terms of the scale of the analysis object, the configurations used in previous studies can be categorized into three typical cases: an isolated building, a single street canyon, and building complexes. Owing to the fact that the simulation of pollutant dispersion around building complexes generally calls for a higher number of computing resources, most of the related studies adopted the Reynolds-averaged Navier-Stokes equations (RANS) method [7; 8; 9; 10; 11; 12], while the large eddy simulation (LES) method [13] was used in limited cases. By contrast, at the level of a single street canyon, both RANS [14; 15; 16] and the LES method [17; 18; 19] were widely used. Moreover, with respect to the level of an isolated building, except for the RANS [20; 21; 22; 23] and LES method [24; 25], the direct numerical simulation method was also adopted in published research [26]. Although there are many sophisticated methods to simulate pollutant dispersion around buildings, two challenges must be addressed when applying the abovementioned semi-empirical methods or numerical modeling methods to this study. (1) The temporary hospital generally consists of building complexes with several types of configurations, around which the pollutant dispersion cannot be simply simulated using semi-empirical methods. (2) On the one hand, considering the urgent construction needs of temporary hospitals, faced by many cities around the world, the purchase of commercial CFD software cannot meet the needs of an emergency response either in time or cost. On the other hand, certain common commercial CFD software, such as Fluent, consumes a significant number of computingresources and takes an extended time to complete the CFD computations [27]. Therefore, to help engineers complete the design of the temporary hospital quickly, open-source CFD software with high computing efficiency and easy operation is the need of the hour. FDS (Fire Dynamic Simulator) is an open-source CFD software developed by the National Institute of Standards and Technology [28]. The software was initially developed for fire simulations. With the gradual enrichment of its functions, it has also been applied to pollutant dispersion simulations [29; 30]. The advantages of the FDS software can be enumerated as follows: (1) the open-source feature of FDS dramatically simplifies the acquisition and installation process and facilitates the promotion of the software; (2) the LES method is inherently adopted by the FDS so that the transient characteristics of the flow field and pollutants can be captured; and (3) compared with commercial CFD software, it is convenient and straightforward for engineers to complete the mesh generation of the computational domain in the FDS so that the design scheme of the temporary hospital can be quickly evaluated. A trial application of the FDS for the pollutant dispersion simulations has been successfully performed by [PERSON] et al. [31; 32]. Owing to the above advantages, FDS is adopted for this study. Aiming to help engineers swiftly finish the design of temporary hospitals, a high-efficiency simulation framework, based on FDS, to analyze the impact of harmful exhaust air is proposed in this study. It should be noted that during the design cycle of the temporary hospital, engineers may be faced with different analysis objects during different design phases. Specifically, in the initial design phase, the feasibility of the conceptual design scheme needs to be quickly evaluated through numerical simulations; in the transition phase, the design scheme of the air outlet and fresh-air intake needs to be simulated and evaluated to ensure that the harmful air, discharged from air outlets, does not pose a secondary infection risk to the fresh-air intakes; in the final phase, it is necessary to quantitatively assess the impact of the harmful exhaust air on the surrounding environment of the temporary hospital.