The benefits of China’s efforts on gaseous pollutant control indicated by the bottom-up emissions and satellite observation

Abstract:

To evaluate the effectiveness of national policies of air pollution control, the emissions of SO₂, NO_X, CO and CO₂ in China are estimated with a bottom-up method from 2000 to 2014, and vertical column densities (VCD) from satellite observation are used to evaluate the inter-annual trends and spatial distribution of emissions and the temporal and spatial patterns of ambient levels of gaseous pollutants across the country. In particular, an additional emission case named STD case, which combines the most recent issued emission standards for specific industrial sources, is developed for 2012-2014. The inter-annual trends in emissions and VCDs match well except for SO_2, and the revised emissions in STD case improve the comparison, implying the benefits of emission control for most recent years. Satellite retrieval error, underestimation of emission reduction and improved atmospheric oxidization caused the differences between emissions and VCDs trend of SO₂. Coal-fired power plants play key roles in SO₂ and NO_X emission reduction. As suggested by VCD and emission inventory, the control of CO in 11^th five year plan (FYP) period was more effective than that in the 12^th FYP period, while the SO₂ appeared opposite. As the new control target added in 12^th FYP, NO_X emissions have been clearly decreased 4.3 Mt from 2011 to 2014, in contrast to the fast growth before 2011. The inter-annual trends in NO₂ VCDs has the poorest correlation with vehicle ownership (R=0.796), due to the staged emission standard of vehicles. In developed regions, transportation has become the main pollutants emission source and we prove this by comparing VCDs of NO₂ to VCDs of SO₂. Moreover, air quality in mega cities has been evaluated based on satellite observation and emissions, and results indicate that Beijing suffered heavily from the emissions from Hebei and Tianjin, while the local emissions tend to dominate in Shanghai.