## 1 Introduction
Catalytic converters, tailored to engine size and aftertreatment type, also influence the NO\({}_{2}\) to NOX ratio, thereby contributing to the overall decrease in emissions. By adopting and combining these innovative approaches, the automotive industry has successfully diminished the levels of NO and NO\({}_{2}\) emissions in car exhaust, mitigating environmental impact and promoting enhanced air quality and public health [30; 31]. In the contemporary landscape, a real-time on-road air quality monitoring network has been established, revolutionizing our ability to assess and manage environmental conditions continuously [32]. While cities have witnessed a reduction in NOx levels over the past few decades, persistent challenges endure, especially in areas identified as hotspots, such as traffic jams [32]. The pronounced mortality burden attributed to NO\({}_{2}\) was predominantly observed in expansive cities and capital cities across western and southern Europe. Sensitivity analyses underscored the significance of the exposure-response function in determining outcomes while demonstrating comparatively lesser sensitivity to variations in baseline mortality values and exposure assessment methodologies [33]. The Hospital Universitario Central de Asturias (HUCA) car park stands out as a specific microenvironment characterized by frequent vehicular agglomerations during peak hours, further complicated by pollutants like nanoparticles and diesel fumes [34]. A startling statistic reveals that diesel-powered vehicles contribute significantly, accounting for roughly 80% of the overall NOx emissions emanating from vehicular traffic [35]. Additionally, NO\({}_{2}\), frequently serving as an indicator of diesel emissions, doubles as a marker for the presence of other anthropogenic pollutants [36]. In a bid to curtail NOx emissions, certain vehicles are now equipped with Selective Catalytic Reduction (SCR) systems employing urea as an effective reducing agent [37]. Among nitrogen oxides, nitrogen dioxide (NO\({}_{2}\)) takes center stage and holds profound implications for human health [24]. Exposure to NO\({}_{2}\) has been unequivocally associated with irritations, coughing, dyspnea, and clinical manifestations such as chest pain and pulmonary edema [38; 39]. Beyond immediate symptoms, NO\({}_{2}\) triggers an inflammatory response in the respiratory system, augmenting susceptibility to lung infections and fostering the formation of potentially carcinogenic nitrosamines [40]. Notably, in the asthmatic population, even low-level exposure at 0.5 ppm for a mere 2 h elicits reported symptoms, including coughing, sputum production, irritation of mucous membranes, and chest discomfort [41]. Recognizing the health risks, international literature has set forth health-protective levels, recommending a short-term exposure guideline range of 0.2 to 0.6 ppm, catering to susceptible individuals and the general population [25]. Additionally, concentrations as minimal as below 10 \(\upmu\)g/m\({}^{3}\) (0.005 ppm) have been found to potentially trigger asthma exacerbation [12]. The genesis of this study lies in the comprehensive analysis of gases within the outpatient parking lot of HUCA in Asturias, Spain. Our primary objective is to meticulously assess the levels of NOx in the subterranean hospital parking facility and derive meaningful recommendations tailored to both the workforce and patients utilizing this integral facility. In doing so, our research aims to contribute nuanced insights to the broader discourse on environmental pollution and healthcare infrastructure, underscoring the salient implications for public health and the evolving landscape of urban living.