Spatiotemporal Variations Of SO₂ And NO₂ Over China Derived From Satellite Remote Sensing

SO₂ and NO_x,which are key precursors of fine particulate matter and ozone,are harmful to both human beings and ecological environment.The Chinese government set emisison reduction targets during the 11^th Five Year Plan?FYP,2006-2010?and the 12^th FYP?2011-2015?to control the emission of SO₂ and NO_x.In this study,spatial distribution and temporal variations of tropospheric SO2 and NO₂ vertical column density?VCD?over China during 2005-2015 were analyzed by utilizing measurements from Ozone Monitoring Instrument?OMI?sensor.The SO₂ concentrations kept decreasing since 2007 except for rebounce in some years and the reduction was significant especially during the 12^th FYP.During the 11^th FYP,rapidly increasing economy and energy consumption accompanying with limited strict control measures of NO_x emissions have led to significant increment of NO₂ VCD over major regions of China,by 15-61%,whereas NO₂ VCD over megacities such as Beijing,Shanghai,and Guangzhou have dropped.During the 12^th FYP,NO_x emission were confirmed as constraint index and reduction of national NO_x emission were required,and furthermore,the promulgation of“Air Pollution Prevention and Control Action Plan”in 2013by the state council assigned even higher demands for NO_x emission control.As a consequence,a decrease of more than 10%of NO₂ VCD over major regions in China were witnessed during the 12^th FYP,especially after 2013.The NO₂ VCD varied during 2005-2015 for the three major regions in China,namely,the Beijing-Tianjin-Hebei region?BTH?,the Yangtze River Delta region?YRD?,and the Pearl River Delta region?PRD?.It first rose and then decreased over BTH and YRD,whereas,it declined continuously over PRD.In 2015,the NO₂ VCD over the three megalopolises were all lower than 2005 levels.Analysis of the emission driving forces showed that installation of denitrification devices and control of vehicle emissions were the main reasons for NO_x emission reduction.This study demonstrated that satellite remote sensing of SO₂ and NO₂ VCD is capable of capturing the impacts of environmental policies on emissions,and implied that results from atmospheric remote sensing could be considered while making decisions and evaluating effectiveness of policies.