Before revision:  Regional variations in CO_2 emissions are significant, with a decrease in China (-9.3\% ) , US (-3.0 \%), Europe ( EU-27 & UK)(-3.3\%) and India (-2.4\%) , respectively.
After revision:  Regional variations in CO_2 emissions are significant, with a decrease in China (-9.3\% ) , US (-3.0 \%), Europe ( EU-27 & UK)(-3.3\%) and the U.S. (-4.2\%). Relative decreases of regional CO2 emissions are consistent with regional nitrogen oxides concentrations observed by satellites and ground-based networks. Despite the unprecedented decreases in CO2 emissions and comparable decreases in economic activities, we monitored decreases in the carbon intensity (Emission per unit of GDP) in China (3.5\%) , respectively.