Observation of ozone and carbon monoxide at Cape Hedo, Japan: Seasonal variation and influence of long-range transport

We performed continuous measurements of O3 and CO at Cape Hedo (26.8°N, 128.2°E, 60 m above sea level), a remote measurement site on Okinawa Island in Japan, in order to investigate the long-range transportation of air pollution from highly polluted regions in East Asia. The O3 and CO concentrations, from January 2002 to May 2004, show maximum values during the winter–spring period with monthly averaged concentrations of 52 and 280 ppbv, and minimum values during the summer period with concentrations of 15 and 81 ppbv, respectively. Based on the transport paths identified by calculating 5-day backward trajectory, air masses are categorized into four groups as follows: “C” for China, “K” for Korea, “J” for Japan, and “O” for the Pacific Ocean. The analysis reveals similar fates for the O3 and CO concentrations for the air masses in the C and K groups, which exhibited the highest monthly averaged concentrations along with high concentrations within the J group where the lowest concentration is found in the O group. Relationship between O3 and CO concentrations reveals positive correlations in the spring and summer months. This suggests that the enhancements of O3 during these seasons are likely to be resulted from the photochemical O3 production in this region.