Analysis of ΔO2/ΔCO2 ratios for the pollution events observed at Hateruma Island, Japan
1National Institute for Environmental Studies, Tsukuba 305-8506, Japan
2Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki 310-8512, Japan
3Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan
*now at: Department of Chemical Engineering, Tokyo University of Aguriculture and Technology 184-8588, Japan
Abstract. 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±0.12, n = 25) and Japan/Korea (1.37±0.15, n = 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.