Long-term (2006-2015) variations and relations of multiple atmospheric pollutants based on multi-remote sensing data...

In this analysis, the Aqua/MODIS aerosol optical thickness (AOD), Aura/OMI tropospheric NO₂ and SO₂ column concentration from 2006 to 2015 were used to statistically analyze the spatial distribution characteristics and variation trends of three polluted parameters from three temporal scales of monthly, seasonal and annual average. The results showed that the minimum values of NO₂ and SO₂ column concentrations both appeared in July and August, and the maximum values appeared in December and January, which was contrary to the variations in AOD. The highly polluted levels were mainly distributed in Shijiazhuang, Xingtai, and Yancheng cities of Hebei Province, and gradually transported to Zhengzhou, Henan Province, north and southwest of Shandong Province, and Tianjin, along the main line of Taiyuan-Linyi, Shanxi Province. AOD and NO₂ had significant differences on the seasonal average scale, whereas SO₂ had little changes. These pollutants had declined year by year since 2011, in the 10-year period, AOD and SO₂ respectively decreased by 17.14% and 10.57%, and only NO₂ rose from 8.69 × 10¹⁵ molecules/cm² in 2006 to 9.10 × 10¹⁵ molecules/cm² in 2015 with the increase rate of 4.79%. Integrated with MODIS-released fire products and the Multi-resolution Emission Inventory for China (MEIC), high AOD values in summer were usually accompanied by frequent biomass burning, and heavy heating demand of coal burning led to largest NO₂ and SO₂ levels in winter. Both inter-annual variations of MEIC NOx and OMI-observed NO₂ responded to emission reductions of vehicle exhaustions positively, but vehicle population in Henan and Shandong provinces need to be further controlled. The significant decline of SO₂ is mainly attributed to the enforcement of de-sulfurization devices in power plants. Our study found that in the treatment of complex atmospheric pollution, in addition to strict control of common sources of emissions from AOD, NO₂ and SO₂, it is also necessary to consider their individual characteristics.