Moderating effect of green space on relationship between atmospheric particulate matter and cardiovascular and cerebrovascular disease mortality in Ningxia, China

Objective: This study explores the moderating effect of green space on the association between atmospheric particulate matter (PM) and cardiovascular and cerebrovascular disease (CCVD) mortality. Methods: Data on CCVD mortality, PM, meteorological factors, and the Normalized Difference Vegetation Index (NDVI) of green spaces in Ningxia from 2010 to 2020 were collected. A time-series generalized additive mixed-effect model (GAMM) was applied to analyze the exposure-response relationship between PM and CCVD mortality. The moderating effect of green spaces was examined using green space buffers of different radii (300 m, 500 m, 1000 m, and 2000 m) and density. Results: There were 150,356 CCVD deaths in Ningxia during the study period. The annual mean concentrations of PM_2.5 and PM₁₀ were 44.44 μg/m³ and 105.30 μg/m³, respectively, with an annual mean NDVI value of 0.25 within a 500 m radius buffer. An increase of 10 μg/m³ in PM_2.5 and PM₁₀ concentrations was significantly associated with an elevated risk of CCVD mortality, with the strongest excess risk (ER) observed at lag07 lag. The ER for PM_2.5 was 1.43% (95% CI: 0.97%, 1.89%), and for PM₁₀ was 0.55% (95% CI: 0.38%, 0.72%). The interaction analysis indicated that higher green space density could moderate the association between PM exposure and CCVD mortality risk. and as the green space buffer zone expanded, the interaction on CCVD mortality risk progressively strengthened. The independent moderation analysis indicated that an increase in green space buffer zone was associated with a reduced risk, and as green space density increased from Q1 to Q3, the ER for PM_2.5-related CCVD mortality decreased from 1.56% to 0.6%, while the ER for PM₁₀-related CCVD mortality decreased from 0.53% to 0.09%. In conclusion, atmospheric PM is associated with increased CCVD mortality risk, while larger green space buffers and higher green space density significantly moderated this association.