## 4 Conclusions  
In this paper, we investigated the applicability of CFD for inhalation exposure assessment from biocide spray in order to solve the spatial problem of the zero-dimensional space model and the time/cost-consuming problem of measurement methods. The CFD results of the sprayed aerosol concentration in various positions were compared with measurement results and the zero-dimensional spray model results. The results of the three methods were compared for 3600 s of physics/simulation. The conclusions can be drawn as follows:  
(1) The zero-dimensional spray model results, the experimental results in the far field and CFD in the far field show relatively good results when compared to each other. However, the spray model shows an underestimation of approximately five times when compared with the CFD results in the near field and experimental results in the near field. In this study, it was shown that exposure evaluation should be performed using CFD or experimental methods rather than the conventional zero-dimensional model.  
(2) When the concentration measurement is performed at various locations using experimental methodology, the cost generated and time required are enormous. The results of measuring the concentration of aerosols at five locations and the CFD results at the same location were compared to show the possibility of evaluating inhalation exposure at various locations using CFD. The experimental result includes an error bar representing the minimum, average and maximum. It can be seen that the CFD value at each measurement location is within the experimental error range. In this study, it was shown that the experimental cost and time problem for inhalation exposure can be reasonably solved using CFD.  
In other words, in the field of exposure science, a guideline for exposure evaluation using CFD was found that complements the shortcomings of the conventional methodology, the zero-dimensional spray model and measurement method.  
However, CFD generates a relatively high computational cost for the simulation of exposure estimation. It is difficult to estimate the exposure according to the user's needs.  
Figure 9: Comparison of measurement result with CFD results in the five measurement positions. The error bar is used due to repeated experiments. The circle is the average of the measurement results, which is the peak concentration. The CFD results according to the measurement position are similar to the measurement results.  
To address these computational cost problems, machine learning modeling methods based on simulation data are used in various industries [29; 30; 31]. Therefore, in future research, we will develop a machine learning model with spatial information as an input variable and spatial concentration as an output variable to predict concentration according to various spatial structures and characteristics.  
[PERSON] analyzed the numerical data and organized the draft paper; [PERSON]-[PERSON] performed the experiment. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Korea Environment Industry & Technology Institute (KEITI) through the Environmental Health Action Program, funded by the Korean Ministry of Environment (MOE) (No. 2012001370007, NTIS 1485012429.  
Not applicable.  
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no potential conflict of interest with respect to the research, authorship and publication of this article.