## 4 Results and Discussion
### Temporal Trends and Variations of Air Pollutants and Meteorological Parameters  
This study analyzed the temporal trends of air pollutant concentrations (PM\({}_{10}\), NO, NO\({}_{2}\), and CO) and meteorological parameters (WS, temperature, RH, and RainF) in Sakarya city between January 2021 and December 2023. The results, supported by Figure 3a-c and detailed statistical findings in Table 2, reveal critical insights into the dynamic interactions between air quality and meteorological conditions. Figure 3: _Cont_. \begin{table}
\begin{tabular}{c c c c c} \hline
**Statistics** & **PM\({}_{\bf 10}\)** & **NO** & **NO\({}_{\bf 2}\)** & **CO** \\ \hline Tau value & 0.000563 & \(-\)0.0235 & \(-\)0.0879 & \(-\)0.167 \\ z-value & \(-\)9.14 \(\times\) 10\({}^{-5}\) & \(-\)9.36 \(\times\) 10\({}^{-5}\) & \(-\)9.95 \(\times\) 10\({}^{-5}\) & \(-\)0.00010675 \\ \(p\)-value & 0.97854 & 0.25939 & 2.54 \(\times\) 10\({}^{-5}\) & 1.32 \(\times\) 10\({}^{-15}\) \\  & & & (<0.01) & (<0.01) \\ Sen’s slope & 3.11771 \(\times\) 10\({}^{-5}\) & \(-\)0.00150658 & \(-\)0.005354839 & \(-\)0.0003175113 \\ \hline \end{tabular}
\end{table} 
Table 2: Mann–Kendall trend analysis results for air pollutants (2021–2023). The temporal trends of air pollutant concentrations are shown in Figure 3a. PM\({}_{10}\) concentrations exhibited no statistically significant long-term trend (\(p\) = 0.97854, tau = 0.000563), indicating persistent sources such as traffic and industrial emissions without substantial mitigation over the study period. Similarly, NO displayed a negligible downward trend, which was not statistically significant (\(p\) = 0.25939, tau = \(-\)0.0235). Conversely, NO\({}_{2}\) concentrations showed a significant decline (\(p\) < 0.01, tau = \(-\)0.0879, Sen's slope = \(-\)0.005354839), reflecting the effectiveness of emission control measures, particularly in reducing nitrogen oxides from vehicular traffic. CO concentrations experienced the steepest and most statistically significant reduction (\(p\) < 0.01, tau = \(-\)0.167, Sen's slope = \(-\)0.0003175113), indicating successful interventions targeting carbon monoxide emissions from industrial and residential sources. Meteorological parameters, illustrated in Figure 3b, exhibited clear seasonal variations. WS and temperature fluctuated in alignment with seasonal climatic patterns, averaging 1.58 m/s and 15.94 \({}^{\circ}\)C, respectively. RH (72.06%) and RainF (2.30 mm) peaked during wetter months, playing a critical role in pollutant dispersion, accumulation, and chemical transformations. WS significantly influenced pollutant dispersion, while RainF contributed to wet deposition, particularly for particulate matter like PM\({}_{10}\). The Mann-Kendall trend analysis, summarized in Table 2, confirmed these observations. Significant trends in NO\({}_{2}\) and CO concentrations underscore the impact of stricter environmental regulations and technological improvements in emission control. On the other hand, the absence of significant trends in PM\({}_{10}\) and NO highlights ongoing challenges in addressing these pollutants, particularly PM\({}_{10}\), which originates from diverse sources such as vehicular emissions, industrial activities, and natural dust resuspension. Figure 3c provides a comparative visualization of the temporal trends of NO\({}_{2}\), NO, CO, and PM\({}_{10}\) concentrations. The significant reductions in NO\({}_{2}\) and CO concentrations reflect the success of emission control measures. In contrast, PM\({}_{10}\) levels show subtle fluctuations  
Figure 3: (**a**) Seasonal trends of air pollutant concentrations (PM\({}_{10}\), NO, NO\({}_{2}\), and CO) in Sakarya (2021–2023); (**b**) seasonal trends of meteorological parameters (WS, temperature, RH, and RainF) in Sakarya (2021–2023); (**c**) comparative trends of PM\({}_{10}\), NO\({}_{2}\), NO, and CO concentrations in Sakarya (2021–2023). with a slight upward tendency, emphasizing the need for enhanced strategies to address particulate matter pollution effectively.