Temporal variations of six ambient criteria air pollutants from 2015 to 2018, their spatial distributions, health risks and relationships with socioeconomic factors during 2018 in China.

•PM, SO2, CO reduced significantly, NO2 was less clear, and O3 increased significantly.•Excess health risks (ER) based on WHO guideline are two times than those from CAAQS guideline.•PM10 rather than PM2.5 contributed the most to ER.•~15%, ~85% and ~95% people in YRD, FWP and JJJ were exposed to polluted air (HAQI > 100) in 2018.•Population-normalized HAQI significantly added the inequality of people exposure to polluted air.