## 4 Discussion
### RQ2: What Thermal Comfort Parameters Were Investigated in the Studies That Analyzed Bus Cabins?
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**References**} & \multicolumn{6}{c}{**Thermal Comfort Parameters**} \\ \cline{2-7}  & **t\({}_{\mathbf{a}}\)** & **V\({}_{\mathbf{a}}\)** & **t\({}_{\mathbf{rm}}\)** & **HR** & **M** & **I\({}_{\mathbf{do}}\)** \\ \hline [PERSON] et al. [11] & x & x & & & & & \\ [PERSON] [48] & x & x & x & x & x & x \\ [PERSON], [PERSON], and [PERSON] [9] & x & x & x & x & x & x \\ [PERSON] et al. [13] & x & x & & & & \\ [PERSON] et al. [18] & x & x & & & & \\ [PERSON] et al. [14] & x & x & x & & & \\ [PERSON] and Daanen [15] & x & x & x & x & x & x \\ [PERSON] [49] & x & x & & x & & \\ [PERSON] and Oz [31] & x & x & x & x & x & x \\ Pimenta and Assuncao [50] & x & & & & & \\ [PERSON] et al. [19] & x & x & x & x & & x \\ [PERSON] et al. [51] & x & x & x & x & & x \\ [PERSON], [PERSON], and [PERSON] [52] & x & & & & \\ [PERSON], [PERSON], and [PERSON] [5] & x & x & x & x & x & x \\ [PERSON] [10] & x & x & & & & \\ [PERSON] et al. [53] & x & x & x & x & x & x \\ [PERSON], [PERSON], and [PERSON] [46] & x & x & & x & & \\ [PERSON] et al. [16] & x & x & x & x & x & x \\ [PERSON] and [PERSON]. [17] & x & x & & & & \\ [PERSON] et al. [54] & x & x & x & x & x & x \\ [PERSON] and [PERSON] [47] & x & & & x & & \\ [PERSON] et al. [55] & x & x & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Thermal comfort parameters considered in thermal comfort studies in bus cabins. (SO2) have also been investigated previously. Particulate matter with diameters of 10 \(\upmu\)m [14; 46], 2.5 \(\upmu\)m [13; 46], and ultrafine [17; 46; 47] represent the suspended pollutants analyzed so far. According to [PERSON] and [PERSON] [17], passengers of buses without air-conditioning felt uncomfortable or very uncomfortable regarding air quality and thermal comfort, whereas passengers who used air-conditioned buses were satisfied in both criteria. Moreover, thermal comfort surpassed air quality regarding the perception of passengers of buses without air-conditioning [17]. According to [PERSON] et al. [11], the front and inferior-back regions of air-conditioned buses were the most critical regarding ozone concentration, which can be aggravated if the doors remain open for longer than 20 s or the occupants are as close as possible to the bus floor. [PERSON] and [PERSON] [47] also investigated pollutant concentrations at different height levels inside the bus. They assessed different floors and concluded that the bottom floor is more conducive to the pollutants examined than the top floor. Regarding the particulate matter of 2.5-\(\upmu\)m diameter, [PERSON] et al. [13] did not find solid results to prove a statistically-significant relationship between these materials and the passengers' mood or airborne diseases. According to [PERSON] et al. [14], increasing or decreasing airflow did not alter the concentration of particulate matter (10 \(\upmu\)m), but it did change the passengers' perception of airflow and reduced the temperature of the bus cabins. [PERSON], [PERSON], and [PERSON] [46] did not find intolerable concentration levels of CO, 10-\(\upmu\)m, 2.5-\(\upmu\)m, or ultrafine particulate matter inside air-conditioned buses. However, the high concentration of CO\({}_{2}\), due to the lack of air change inside this closed environment, drew the authors' attention because of the high risk of air transmission of the Influenza virus. RQ\({}_{4}\): What International Standards of Thermal Comfort Did the Studies that Analyzed the Thermal Conditions of Bus Cabins Follow? Table 10 displays the standards and models of thermal comfort employed in the studies conducted in bus cabins.