In-situ observations of atmospheric CO₂ and O₂ concentrations at Hateruma Island (HAT, 24° N, 124° E) often show synoptic scale pollution events when air masses are transported from East Asian source regions. We calculate the regression slopes (-ΔO₂/ΔCO₂ molar ratios) of the correlation plots between O₂ and CO₂ for selected pollution events observed between October 2006 and December 2008. The observed -ΔO₂/ΔCO₂ ratios vary from 1.0 to 1.7. Categorizing the air mass origins for the pollution events by using back trajectory analysis, we find that there is a significant difference in the average -ΔO₂/ΔCO₂ ratios between events from China (1.14&plusmn;0.12, <i>n</i> = 25) and Japan/Korea (1.37&plusmn;0.15, <i>n</i> = 16). These values are comparable to the -O₂:CO₂ molar exchange ratios, which are estimated from the national fossil fuel inventories from CDIAC. Simulations using a particle dispersion model reveal that the pollution events at HAT are predominantly CO₂ emissions from the combustion of fossil fuels in East Asian countries, which is consistent with the above observational results. Although the average value of the model-predicted -ΔO₂/ΔCO₂ ratios for Japan/Korea origin is underestimated in comparison with the observation, that for China origin agree well with the observation. The sensitivity experiment suggests that the -ΔO₂/ΔCO₂ ratio at HAT reflects about 90% of the change in the -O₂:CO₂ exchange ratio for the fossil carbon emissions from China.