APEC blue was coined to describe the impact of short-term curbs on air pollution during the Asian-Pacific Economic Cooperation (APEC) Summit organized in Beijing in November 2014 and has been a hot topic among both general public and scientific sector in China. The consensus that gaseous agents NO2 and SO2 are greatly reduced in response to the control and restriction strategies implemented during the Summit period is shared by earlier literature. However, the re-examination of APEC blue conducted in the present study comes to a more contrasted conclusion. The remarkable drop in NO2 abundances is confirmed in terms of both surface concentration and vertical column, whereas corresponding SO2 changes are found to be marginal and not statistically significant, indicating that the decline of SO2 was more tied to natural or random variability rather than externally forced. To explain the contrasted responses of NO2 and SO2 during the APEC summit, short-term variations of these species are further placed in the context of a longer term perspective, which reveals a striking contrast in the pathways of the secular tendency in NO2 and SO2 emissions and corresponding measured abundances of both pollutants. On the one hand, NO2 emissions exhibit a sharp rise by 30–50% from 2006-2010 to 2011–2014; on the other hand, SO2 emissions have undergone a gradual decrease in the last decade and have currently returned to their pre-2000 level. Therefore, short-term control measures are expected to be more effective in reducing the levels of NO2 than SO2.