Non-linear relations between life expectancy, socio-economic, and air pollution factors: a global assessment with spatial disparities

Influential factors of socio-economic and air pollution on life expectancy (LE) show complexity. The investigations of non-linear functions of LE, socio-economic, and air pollution factors have not been largely conducted, and spatial and temporal differences of the linear or non-linear relations between LE and the influential factors have been obscured across countries in the world. In this study, the non-linear relations between LE and factors of per capita gross national income (GNIpc), urban population rate (UPR), and fine-particulate (PM2.5) were estimated from 2000 to 2015 by using a generalized additive model (GAM). The collected data included the 219 countries and regions with sufficient data and covers the period 2000–2015. The results demonstrate that at the global level, the GNIpc plays a stable and significant non-linear role in LE, while the non-linear relationships between UPR, PM2.5, and LE are not significant. The temporal variation was further investigated that the non-linear effect of PM2.5 on LE is gradually strengthened, and the non-linear effect of UPR on LE shows a weakened trend. However, GNIpc always plays a significantly non-linear role in the LE level. Furthermore, the spatial difference in the non-linear relations among different continents is detected. In sum, it cannot be ignored the non-linear effects of socio-economic and air pollution factors on LE at a global scale and across different continents.