On the regional background levels of carbon monoxide observed in East Asia during 1991∼2004

The carbon monoxide (CO) concentrations observed in Mt. Waliguan in China (WLG), Ulaan Uul in Mongolia (UUM), Tae-ahn Peninsula in Korea (TAP) and Ryori in Japan (RYO) were analysed between 1991 and 2004. The average annual concentration of CO, a toxic air pollutant, was the highest at TAP (233 ± 41 ppb), followed by RYO (171 ± 36 ppb), UUM (155 ± 26 ppb) and WLG (135 ± 22 ppb). CO tends to be highest in spring and lowest in summer in East Asia, with the exception of WLG. TAP had the highest CO concentrations in all seasons compared with WLG, UUM and RYO and displays a wide short-term variability in concentration. This is caused by large-scale air pollution owing to its downwind location, close to continental East Asia. CO concentrations observed at TAP were analysed as follows: according to the origin of the isentropic backward trajectory and its transport passage, as continental background airflows (CBG) measuring 216 ± 47 ppb, regionally polluted continental airflows (RPC) measuring 316 ± 56 ppb, oceanic background airflows (OBG) measuring 108 ± 41 ppb and partly perturbed oceanic airflows measuring 161 ± 6 ppb. The high concentrations of CO at TAP are because of the airflow originating from the East Asian continent, rather than the North Pacific. RPCs, which pass through eastern China, appear to have high CO concentrations in spring, autumn and winter. OBGs, however, are affected by North Pacific air masses with low CO concentrations in summer. National Oceanic and Atmospheric Administration satellite images and the Goddard Earth Observing System (GEOS)-Chem simulation model confirmed that a large-scale air pollution event originated in eastern China and reached the Korean Peninsula and the Korea East Sea by way of the Yellow Sea. It is noteworthy that the overall trend at TAP does not show an increase despite the fact that energy use in China approximately doubled from 1991 to 2004.