## 4 Discussion  
The results indicate that all measured values fall below established occupational exposure levels for both NO and NO\({}_{2}\), with average levels generally remaining at or below 10% of the occupational exposure limit values (OELVs), except for specific instances (e.g., NO\({}_{2}\) on 19 July 2019 and NO on 15 February 2021), where values approached 20% OELV. While punctual measurements recorded maximum levels of 7.3 ppm for NO and 1.17 ppm for NO\({}_{2}\), these instances were of a short duration, lasting less than one minute. However, it is essential to note that these exposure limit values are primarily designed for occupational use, and the HUCA parking facility caters to a diverse user base, including vulnerable patients and children attending for medical needs. In light of this, there is a critical need to revisit the current exposure limit standards, considering the unique characteristics of parking facilities associated with healthcare institutions. Despite overall compliance with occupational standards, environmental values raise concerns. Approximately 75% of the sampled days witnessed maximum one-hour NO\({}_{2}\) concentrations surpassing 70% of the World Health Organization (WHO) recommended value, with around 20% of the sampled days exceeding the 0.1 ppm NO\({}_{2}\) level in one hour as per WHO guidelines. The environmental assessment of NO\({}_{2}\) levels revealed a concerning pattern, with a maximum reported level of 0.165 ppm for a one-hour average, exceeding the World Health Organization (WHO) recommendations. Notably, around 20% of the sampled days exhibited at least one hour of NO\({}_{2}\) concentrations surpassing WHO guidelines, particularly prevalent around 11:00 am. The dynamic nature of NO\({}_{2}\) levels during peak hours raises concerns about potential health risks, especially for the vulnerable population. Given that  
Figure 3: Percentage of working days and NO\({}_{2}\) levels (for at least one hour). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & & & & \multicolumn{3}{c}{**NO\({}_{2}\)**} & \\ n\({}^{\circ}\) & **Date** & **City** & **Start** & **Finish** & **h** & **Average** & **Max** & **Average** & **Max** (**1 h** \\  & & & & **(ppm)** & **(ppm)** & **(ppm)** & **(ppm)** & **(ppm)** & **Average** \\ \hline
1 & 21/11/2023 & Salamanca P-2 & 7:30 & 16:20 & 8:50 & 0.03 & 0.7 & 0.02 & 0.18 & 0.039 \\
2 & 21/11/2023 & Salamanca P-1 & 7:56 & 16:41 & 8:45 & 0.08 & 0.8 & 0.06 & 0.2 & 0.085 \\
3 & 27/04/2023 & Aviles P-2 & 7:36 & 14:27 & 6:51 & 0.47 & 1.8 & 0 & 0.11 & 0.001 \\
4 & 27/04/2023 & Aviles P-3 & 7:48 & 14:21 & 6:33 & 0.6 & 1.8 & 0.01 & 0.1 & 0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: NO and NO\({}_{2}\) measurement summary of other hospitals’ underground car parks. asthma and other respiratory conditions worsen with exposure to NO2, individuals with sensitivities should avoid underground environments in such conditions. Despite compliance with legal requirements for NOx levels in a new parking facility (established in 2014), the study underscores the need for heightened awareness and precautionary measures, especially during peak hours. Vulnerable patients are strongly advised to utilize outdoor parking spaces whenever possible, with indoor parking discouraged during traffic peaks, especially in level -2. Visitors are encouraged not to linger in the parking area while waiting for consultations, and workers are advised to minimize their time spent in vehicles, opting instead for enclosed spaces with a fresh supply of outside air. The temporal patterns in the maximum one-hour average NO2 concentration indicate that peak levels typically manifest around 11:00 am, aligning with increased vehicular activity within the parking facility. A continuous traffic flow is observed until approximately 4:00 pm, after which concentrations experience a significant decline.