# Prediction and Comparison of In-Vehicle CO\({}_{2}\) Concentration Based on ARIMA and LSTM Models
## 1 Introduction
The majority of standards prescribe a CO\({}_{2}\) concentration of 1000 ppm. Based on the aforementioned measurement results, it was observed that in most cases, both small and large vehicles exhibited a CO\({}_{2}\) concentration exceeding 1000 ppm during operation, with some even surpassing 5000 ppm. Comparing the existing standards, it was observed that the concentration of CO\({}_{2}\) in numerous test vehicles exceeded the prescribed levels stipulated by the standards. Although the duration of actual tests rarely exceeds 1 h or 8 h, studies have indicated that exposure to 1000 ppm to 5000 ppm can impact both health and driving behavior. ASHRAE reports that indoor CO\({}_{2}\) concentrations are linked to an increased occurrence of self-reported sick building syndrome symptoms [15]. Additionally, the in-vehicle CO\({}_{2}\) may affect the body's perception \begin{table}
\begin{tabular}{c c} \hline
**Institution** & **Regulated or Suggested Concentration of CO\({}_{2}\) (ppm)** \\ \hline The American Society of Heating, Refrigerating, and & 1000 [15] \\ Air-Conditioning Engineers (ASHRAE) & 1000–1500 [16] \\ U.S. Occupational Safety and Health Administration (OSHA) & 1000 (1 h average) [17] \\ National Bureau of Disease Control and Prevention of China & 1000 (Non-residential buildings) \\ French rules & 1300 (No smoking area) [18] \\ Taiwan Environmental Protection Administration in China & 1000 (8 h CO\({}_{2}\)) [11] \\ Hong Kong Environmental Protection Administration in China & 2500 (1 h CO\({}_{2}\) for level 1 for buses) [11] \\ \hline \end{tabular}
\end{table} 
Table 1: CO\({}_{2}\) standards established by various institutions. of comfort [18], and it may cause an increase in diastolic blood pressure [19], affecting ride comfort. It can lead to fatigue and drowsiness, impacting cognitive capabilities, which reduce reaction time and concentration. Ultimately, this affects the driver's decision-making ability and judgment, creating a potential hazard for traffic safety [20; 21; 22]. Some authority agencies have pointed out that this negative impact can lead to traffic accidents., as noted by the Royal Malaysian Traffic Police, who identify driver fatigue and inattention as primary causes of such incidents [23]. A study conducted by the American Automobile Association revealed that fatigued drivers were responsible for three-and-a-half times more crashes than that reported in news accounts from 1999-2008 [24]. A report released by the National Highway Traffic Safety Administration (NHTSA) indicated that at least 83,000 vehicle accidents were caused by driver fatigue and drowsiness; these accidents led to 37,000 injuries and 900 fatalities [25]. In order to mitigate the occurrence of traffic accidents and maintain a comfortable cabin environment, it is important to precisely forecast and regulate the in-vehicle CO\({}_{2}\) concentration level, while also alerting occupants prior to reaching levels that may impact behavior or physical health. Consequently, several scholars have conducted research on models for calculating the CO\({}_{2}\) concentration in vehicles. [PERSON] [26] developed a mathematical model that accurately predicts the concentrations of CO\({}_{2}\) during RC ventilation mode; [PERSON] et al. [6] employed a first-order mass balance equation to simulate variations in CO\({}_{2}\) inside a vehicle while driving; [PERSON] [27] developed a more comprehensive calculation model, including passenger count, cabin volume, and leakage rate, among others; [PERSON] et al. [13] investigated the impact of seasonal variations and developed a semi-empirical model. These models were developed based on the principles of CO\({}_{2}\) mass balance or control volume-mass conservation. Furthermore, [PERSON] and [PERSON] [22] integrated the CO\({}_{2}\) generation rate with the air change rate, vehicle characteristics, and driving conditions to develop a model for assessing in-vehicle CO\({}_{2}\) accumulation.