<p>Potential changes in the air pollutant spatial gradient may modify the performance of air quality networks, affecting function fulfillment. This study aims to elucidate, for the first time, whether the air quality networks’ design may be sustained over time. For that, temporal-spatial indicators were assessed in the long term. Particulate matter data (2005–2022) monitored by two target air quality networks (interior southwest European region) were regarded as a case study. The approach was applied to 2005–2022 particulate matter data. Broadly, the implementation of current European legislation (from 2008) has translated into a noticeable decrease in pollution levels. Polluting disparities were observed within the same fixed station category (urban, suburban, and rural). Diverse fixed monitoring stations showed different long-term pollution sceneries, evidencing varied exposure contexts. Distinct spatial patterns (quali- and quantitatively) were observed at global and local levels. Although the annual average PM_2.5/PM₁₀ ratio remains stable, suggesting common emission sources, the legislative limit exceedances are not sustained over the study due to fluctuating environmental conditions. Meteorological variables, particularly temperature, consistently impact particulate matter. Variable long-time environmental pollution situations may affect the performance of air quality networks. Based on a solid body of evidence, this work reveals needing to assess the long-time performance of air quality networks to secure the adequate fulfillment of their functions, given that non-redundant stations can become redundant ones and vice versa, thereby serving as a helpful methodology to complement current European air quality directives due to the lack of harmonized methodologies to achieve such an objective.</p>