National Trends in Ambient Air Pollutants and Cause-Specific Mortality in Türkiye, 2018–2024: An Ecological Time-Trend Study

Ambient air pollution remains an environmental health concern, yet national evidence in Türkiye integrating multiple pollutants, WHO guideline exceedance, mortality patterns, and monitoring network changes is limited. We analyzed seven annual observations (2018–2024) for PM10, SO2, CO, NO2, and O3. For each pollutant-year, the national indicator was the unweighted mean of eligible station annual means from official bulletins; mortality outcomes were crude national rates. Linear trends were estimated by OLS regression and assessed alongside Mann–Kendall tests, Sen’s slopes, and strict common-station sensitivity analyses. PM2.5 was excluded because monitoring coverage and annual reporting were not sufficiently comparable across years. PM10 decreased from 50.4 to 41.0 µg/m3 and SO2 from 13.2 to 8.5 µg/m3, with significant negative linear trends. The all-station NO2 indicator increased from 29.2 to 34.4 µg/m3, but its linear trend was not statistically significant (slope = 0.879 µg/m3/year; p = 0.055) and was absent in the common-station analysis (slope = −0.021; p = 0.950). PM10 guideline exceedance remained nearly universal, and NO2 exceedance remained high. Among mortality outcomes, only neoplasm mortality declined significantly. Air quality trends were pollutant-specific and, for NO2, sensitive to monitoring network composition. The ecological design does not permit causal inference regarding pollutant–mortality relationships.