Associations of air pollution and greenness with mortality in Greece: An ecological study

Epidemiological studies have documented the adverse effects of long-term exposure to fine particulate matter (PM_2.5) on health, while there has been less research on the effects of nitrogen dioxide (NO₂), black carbon (BC) and especially ozone (O₃). Furthermore, there is limited evidence for the synergistic effects of exposure to pollutants and greenness. We investigated the association of long-term exposure to air pollution and greenness with natural-cause, cardiovascular and respiratory mortality in Greece using an ecological study design.

Mortality and socioeconomic data were obtained from 1035 municipal units from the 2011 census data. Annual average PM_2.5, NO₂, BC and O₃ concentrations for 2010 were derived from 100 × 100 m surfaces predicted by hybrid LUR models. The normalized difference vegetation index was used to assess greenness. We applied Poisson regression models on standardized mortality rates adjusted for socioeconomic indicators and lung cancer rates, accounting for spatial autocorrelation. The analysis was conducted initially for the whole country and then separately for urban and rural areas. We assessed interactions between pollutants and greenness and applied two-exposure models.

An interquartile range (IQR) increase in PM_2.5, NO₂ and BC was associated with increases in natural-cause mortality (Relative Risk (RR) 1.09, 95% confidence interval (CI): 1.08, 1.11; RR 1.03 (95% CI: 1.03, 1.04) and RR 1.02 (95% CI: 1.02, 1.03), respectively), while PM_2.5 and NO₂ were also associated with cause-specific mortality. Greenness was associated with lower natural-cause (RR 0.95, 95% CI: 0.94, 0.96 per IQR) and cause-specific mortality. For all outcomes we estimated a protective association with O₃ (natural-cause mortality RR 0.79, 95% CI: 0.76, 0.82 per IQR). All associations were stronger in urban areas. We estimated negative statistically significant interactions between air pollution and greenness for respiratory morality and positive ones for cardiovascular mortality. Estimates were mostly robust to co-exposure adjustment.

Our findings support associations of air pollution and greenness with mortality, both in urban and rural areas of Greece. Further research is needed to elaborate on the synergies in cause-specific mortality. Our results on the interactions between pollutants and greenness may imply differential biological mechanisms for cause-specific mortality and warrant further investigation.