Analysis of ΔO₂/ΔCO₂ ratios for the pollution events observed at Hateruma Island, Japan

Abstract. Pollution events extracted from the in situ observations of atmospheric CO₂ and O₂ mixing ratios at Hateruma Island (HAT, 24° N, 124° E) during the period from October 2006 and December 2008 are examined. The air mass origins for the pollution events are categorized by using back trajectory analysis, and the oxidative ratios (OR = −O₂:CO₂ molar exchange ratio) for selected pollution events are calculated. We find that there is a significant difference in the average oxidative ratios between events from China (OR = 1.14 ± 0.12, n = 25) and Japan/Korea (OR = 1.37 ± 0.15, n = 16). These values are in a good agreement with the national average oxidative ratios for the emissions from fossil fuel burning and cement production (FFBC) in China (OR_FFBC = 1.11 ± 0.03) and Korea/Japan (OR_FFBC = 1.36 ± 0.02). Compared with the observation, simulations of the atmospheric O₂ and CO₂ mixing ratios using Lagrangian particle dispersion models do a good job in reconstructing the average oxidative ratio of the pollution events originating in China but tend to underestimate for events originating in Japan/Korea. A sensitivity test suggests that the simulated atmospheric oxidative ratios at HAT are especially sensitive to changes in Chinese fuel mix.