Post-Pandemic Stability and Variability of Urban Air Pollutants in Mexico City: A Multi-Pollutant Temporal Analysis for Environmental Sustainability

Urban air quality is a key component of environmental sustainability and public health in large metropolitan areas. Following the substantial but temporary improvements in air quality observed during the COVID-19 lockdowns, it remains unclear whether structural changes in urban air pollution have persisted in the post-pandemic period. This study analyzes the temporal dynamics of major atmospheric pollutants in Mexico City between 2021 and 2024, including CO, NO₂, NOₓ, O₃, PM₁₀, PM₂.₅, and SO₂, using hourly data collected by the official air quality monitoring network SIMAT. Annual and monthly median concentrations were computed to reduce the influence of extreme values and short term pollution episodes. Station level monotonic trends were evaluated using the non-parametric Mann–Kendall test, complemented by Sen’s slope estimator to quantify the magnitude and direction of change. Absolute and relative changes between 2021 and 2024 were also analyzed to capture incremental variations not reflected by trend significance tests, together with hourly monthly analyses to characterize diurnal and seasonal patterns. Results indicate that no statistically significant monotonic trends were detected for any pollutant across the analyzed stations (p > 0.05), suggesting an overall stabilization of air quality levels during the post-pandemic period. Nevertheless, mod-erate increases in annual median concentrations were observed at specific locations, particularly for PM₁₀, PM₂.₅, NO₂, and NOₓ, with relative changes ranging from ap-proximately 5% to 35%. Persistent diurnal and seasonal patterns were identified, closely associated with traffic activity, photochemical processes, and meteorological conditions. These findings suggest that, although no robust long-term trends are evident, incre-mental increases and stable temporal structures remain relevant from a sustainability perspective. Continued monitoring and targeted air quality management strategies are therefore necessary to support long-term urban environmental sustainability.