Long-term (2005-2015) tropospheric nitrogen dioxide (NO2) column data recorded by the satellite-borne Ozone Monitoring Instrument (OMI) in East Asia were analyzed to investigate annual trends on an national basis and their potential causes. We found an evident decrease of 6% year-1 in the NO2 level over China after 2011. The grid-basis trend analysis implies that the rapid decrease occurred on a provincial or larger spatial scale and was likely due to a nationwide action such as the widespread use of denitrification units. In Japan and South Korea, a turnaround indicating an increase was observed after 2013 and 2012, respectively. As a consequence, the tropospheric NO2 pollution level in East Asia was found to be recovered to the 5-year-ago level in 2015.
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