Spatiotemporal trend analysis for fine particulate matter concentrations in China using high-resolution satellite-derived and ground-measured PM2.5 data.

Atmospheric fine particulate matters (PM2.5) have raised global concerns because of their markedly adverse effects on public health and environmental quality. In parallel with technological variations and social changes in the evolving industrialization pathways in China, there is an acute need to evaluate the long-term spatiotemporal trend of PM2.5 concentrations across China after years of elevation. Toward this end, an integrated high-resolution satellite-derived (1998-2016) and ground-measured (2015-2017) PM2.5 data base was applied. Satellite-derived annual mean PM2.5 grids were firstly validated via comparison with collocated surface in situ PM2.5 measurements and were then used for trend analyses. The estimated linear trends from gridded PM2.5 data indicated that PM2.5 concentrations in China increased mainly before 2008 and have decreased since then, with prominent decreases observed primarily in south China. To corroborate the satellite-based PM2.5 trend estimations, surface in situ PM2.5 measurements from the period from 2015 to 2017 were applied to further evaluate the decreasing rate after 2014, at which time the Chinese "Air Pollution Prevention and Control Action Plan" was enforced. The results revealed that the national mean PM2.5 concentrations decreased by about 6.5 μg/m3 from 2015 to 2017, with prominent decreases (by a rate of 5-10 μg/m3 per year) observed primarily associated with large PM2.5 concentrations in Central China, North China, Northeast China, and East China during the period from October to December. Our systematic trend assessment provides a deepened understanding of PM2.5 variations across China in the past few years in association with the newly promoted action plan and offers a brief guideline for relevant policy making in the future.