Individual and interactive effects of atmospheric PM_2.5 and O₃ on mortality of circulatory system diseases in Ningxia

Background The impact of atmospheric fine particulate matter (PM_2.5) and ozone (O₃) on the mortality of circulatory system diseases cannot be ignored. However, whether the interaction between PM_2.5 and O₃ can affect population health is rarely reported and requires study.

Objective To investigate the individual and interactive impacts of atmospheric PM_2.5 and O₃ on the mortality of circulatory system diseases in the population of Ningxia region.

Methods The data of 119647 deaths due to circulatory system diseases, daily average concentrations of atmospheric pollutants, and meteorological data in Ningxia from 2013 to 2020 were retrieved. PM_2.5 was divided into low, medium, and high concentrations according to the primary and secondary national limits (35 and 75 μg·m⁻³) of the Ambient air quality standards. Similarly, O₃ was divided into low, medium, and high concentrations according to the national limits (100 and 160 μg·m⁻³). Using a generalized additive mixed model based on quasi Poisson distribution, the impacts of atmospheric PM_2.5 and O₃ as well as their interaction on the mortality of circulatory system diseases were analyzed using the population data of Ningxia region.

Results During the target period, males and the ≥ 65 year group accounted for larger proportions of deaths due to circulatory system diseases (55.47% and 79.87% respectively). The daily average concentration of PM_2.5 (40.25 μg·m⁻³) exceeded the national primary limit. In the single pollution model, the highest cumulative lag effects for mortality from circulatory system diseases were PM_2.5 exposure over previous 1 d (lag01) and O₃ exposure for previous 2 d (lag02), and their excess risk (ER) values were 1.03% (95%CI: 0.67%, 1.40%) and 1.02% (95%CI: 0.57%, 1.50%), respectively. The results of concentration stratification analysis showed that the most significant risks of death from circulatory system diseases ER (95%CI): 1.12% (0.32%, 1.92%) and 0.95% (0.13%, 1.79%) respectively were found at medium PM_2.5 and O₃ concentrations. The interaction analysis revealed that under, a synergistic effect on the risk of death from circulatory system diseases was identified (relative excess risk due to interaction=3.08%, attributable proportion of interaction=2.90%, synergy index=1.89) when considering the coexistence of PM_2.5 and O₃ above the primary limit. As the concentrations of PM_2.5 and O₃ increased, the synergistic effect increased the risk of death from circulatory system diseases in the general population, men, women, and the ≥ 65 years group.

Conclusion Both atmospheric PM_2.5 and O₃ can increase the risk of death from circulatory system diseases, and the two pollutants have a synergistic effect on the risk of death from circulatory system diseases.