Hitoshi Mukai

CO2 surface fluxes at grid point scale estimated from a global 21 year reanalysis of atmospheric measurements

This paper documents a global Bayesian variational inversion of CO2 surface fluxes during the period 1988-2008. Weekly fluxes are estimated on a 3.75 degrees x 2.5 degrees (longitude-latitude) grid throughout the 21 years. The assimilated observations include 128 station records from three large data sets of surface CO2 mixing ratio measurements. A Monte Carlo approach rigorously quantifies the theoretical uncertainty of the inverted fluxes at various space and time scales, which is particularly important for proper interpretation of the inverted fluxes. Fluxes are evaluated indirectly against two independent CO2 vertical profile data sets constructed from aircraft measurements in the boundary layer and in the free troposphere. The skill of the inversion is evaluated by the improvement brought over a simple benchmark flux estimation based on the observed atmospheric growth rate. Our error analysis indicates that the carbon budget from the inversion should be more accurate than the a priori carbon budget by 20% to 60% for terrestrial fluxes aggregated at the scale of subcontinental regions in the Northern Hemisphere and over a year, but the inversion cannot clearly distinguish between the regional carbon budgets within a continent. On the basis of the independent observations, the inversion is seen to improve the fluxes compared to the benchmark: the atmospheric simulation of CO2 with the Bayesian inversion method is better by about 1 ppm than the benchmark in the free troposphere, despite possible systematic transport errors. The inversion achieves this improvement by changing the regional fluxes over land at the seasonal and at the interannual time scales. (Less)

Characterization of a humic acid-like brown substance in airborne particulate matter and tentative identification of its origin

Abstract A brown substance having the solubility characteristics of humic acid was extracted from airborne particulate matter sampled in a rural area of Japan. This brown substance contributed 0.6–3% of the total carbon in airborne particulate matter. This fraction also contained pollen protein in samples collected during the pollen season. Patterns of elution from gel permeation chromatography suggested a molecular weight range from 500 to 10,000, with a still higher upper limit for one sample. The infrared spectra were compared with those of humic acid from the local soil, extracts from dead leaves, smoke from burning plant matter, and soot from automotive exhaust, all possible sources of the brown substance. The closest similarity was with the extract smoke. This identification is strengthened by lack of correlation of the brown substance with aluminum, a tracer for soil content, and a value of K/Fe ratio in the associated particulate matter higher than any plausible source other than combustion. It is probable that the primary source of this brown, high molecular weight acidic materials is agricultural burning.

Lead isotope ratios of airborne particulate matter as tracers of long‐range transport of air pollutants around Japan

The use of airborne lead isotope ratios as tracers of long-range transport of air pollutants in the Asian region was evaluated using air trajectory analysis. Airborne particulate matter was collected in various seasons from 1988 to 1991 at the Oki Islands located between the Asian continent and Japan. Air masses coming from Japan had lead isotope ratios nearly equal to those measured on mainland Japan. Air masses from the Asian continent had less radiogenic isotope ratios than those from Japan. Trajectory analysis showed that these less radiogenic values could be used to further subdivide Asian air masses as having come from one of three regions: the southern part of the Korean Peninsula, north China, and Russia. The isotope ratios of the samples classified into three regions were close to previously reported values measured in each region, except for those assigned to Korea, where it is believed that the ratios are currently changing. It was concluded that lead isotope ratios were reliable tracers of the long-range transport of air pollutants, especially when used in conjunction with air trajectory analysis.

Long‐range transport of ozone in the East Asian Pacific rim region

Measurements of surface ozone were conducted at three remote island sites in the East Asian Pacific rim region during the Pacific Exploratory Mission-West (A) campaign period in September–October, 1991. The ozone concentrations observed at the three measurement stations at Oki and Okinawa, Japan, and Kenting, Taiwan, had similar ranges varying between 6–63, 8–58, and 4–65 ppb, respectively, except for one event of short-range transport of polluted air at Kenting. Day-to-day variations have been analyzed by using backward air parcel trajectories on isentropic surfaces. The results showed that continental air masses which originated from northwestern Asia and passed through the high anthropogenic emission region of East Asia contained the highest concentration of ozone, 30–60 ppb with an average of 43–45 ppb at the three stations. In contrast, the lowest concentrations were observed for air parcels originating from the mid-Pacific and transported without mixing with the continental outflow. These parcels contained 5–20 ppb of ozone with the average of 11, 15, and 9 ppb at Oki, Okinawa, and Kenting, respectively. The air parcels from the South China Sea contained 22 and 18 ppb of ozone at Okinawa and Kenting, respectively, which were higher than those from mid-Pacific. Continental air mass from the north-northeast to Oki containing 35–40 ppb ozone with the average of 37 ppb was recognized as continental “background.” The high ozone concentrations in the northwesterly continental outflow exceeding the background was ascribed to photochemical buildup in the planetary boundary layer.

Aircraft measurements of the concentrations of CO2, CH4, N2O, and CO and the carbon and oxygen isotopic ratios of CO2 in the troposphere over Russia

About 370 air samples were collected using aircraft in the troposphere over Russia in the summers of 1992, 1993, and 1994. These were then analyzed for the CO2, CH4, N2O and CO concentrations, as well as for δ13C and δ18O of CO2. Measured vertical profiles of tropospheric CO2 showed that the concentration increased with height over all locations. In the lower troposphere over the wetland and taiga regions, extremely low CO2 concentrations of 335–345 parts per million by volume (ppmv) were often observed. Measured values of δ13C and the CO2 concentration were negatively correlated with each other, the rate of change in δ13C with respect to the CO2 concentration being about −0.05‰/ppmv. This implies that the variations in the CO2 concentration observed over Russia in the summer are primarily caused by terrestrial biospheric activities. In the middle and upper troposphere, the CO2 concentration and δ13C showed systematic differences between each other in 1992, 1993, and 1994, probably due to their secular changes. The δ18O and CO2 observed in the lowest part of the troposphere over east and west Siberia were also negatively correlated with each other, with the rate of change in δ18O with respect to CO2 estimated to be about −0.1 l‰/ppmv. This relation may be caused by isotopic equilibrium of oxygen in CO2 with soil water through respiration of living plants and decomposition of organic matter and with chloroplast water in leaves through photosynthesis of living plants. In contrast to CO2, the CH4 concentration decreased with height. Extremely high CH4 concentrations were observed over the west Siberian lowland, owing to a large amount of CH4 emitted from wetlands. The N2O concentrations were fairly constant through the troposphere over all locations covered by this study, with an average value of about 311 parts per billion by volume (ppbv). The CO concentrations also showed vertical profiles, with a small gradient over natural wetlands, taiga, and tundra. High values of the CH4, CO, and CO2 concentrations were observed over Moscow, owing to emissions of the respective gases by human activities in an urban area. It was also found that over natural wetlands and tundra the CO2 and CH4 concentrations were negatively correlated with each other, reflecting a strong biospheric CO2 uptake and CH4 emissions from wetlands. The relationship between the CH4 and CO concentrations was strongly positive over areas with their anthropogenic and natural sources; the relationship was only slightly positive over wetlands, possibly due to CO emissions from wetlands and/or photochemically produced CO.

Long-term variation of chemical composition of atmospheric aerosol on the Oki Islands in the Sea of Japan

Abstract Chemical composition in aerosols collected on the Oki Islands, which are located in the Sea of Japan, were measured for 4 1 2 years (1983–1988) and their variations were investigated from the viewpoints of aerosol background level and transport of aerosols from both the mainland of Japan and the Asian Continent. Kosa, which is soil dust from the Asian deserts, strongly influenced the variations of the concentration of soil-derived components in aerosol, which showed high concentrations every spring and November. Sulfate had a good correlation with V in the variation and their concentrations increased in summer as the result of the transport of the aerosol from the mainland of Japan. Whereas high Pb concentration in winter was presumed to be attributed to the contribution of lead-enriched aerosol transported from the Asian Continent by the northwest monsoon. The differences of aerosol composition between summer and winter were seen in the ratios of Pb/Zn and Sulfate/V, which may be good indicators for the characterization of aerosol in Asian region. Long-term trends of changing of aerosol composition were also studied, and only C indicated a slight increase for 4 years.

Distribution of methyl iodide, ethyl iodide, bromoform, and dibromomethane over the ocean (east and southeast Asian seas and the western Pacific)

Ambient concentrations of four marine-derived halocarbons (methyl iodide, ethyl iodide, bromoform and dibromomethane) and two man-made halocarbons (trichloroethylene and tetrachloroethylene) were measured during western Pacific cruises and east and southeast Asian cruises. Ethyl iodide was detected in the atmosphere for the first time and was identified as an atmospheric iodine source compound. Bromoform concentrations were positively correlated with those of dibromomethane, and methyl iodide showed variations similar to those of ethyl iodide. However, there was no correlation between the bromocarbons and the iodocarbons. The concentrations of methyl iodide and ethyl iodide changed more markedly, possibly owing to higher rates of photodecomposition of iodocarbons.

Correlations and emission ratios among bromoform, dibromochloromethane, and dibromomethane in the atmosphere

[1] Bromoform (CHBr 3 ), dibromochloromethane (CHBr 2 Cl), and dibromomethane (CH 2 Br 2 ) in the atmosphere were measured at various sites, including tropical islands, the Arctic, and the open Pacific Ocean. Up to 40 ppt of bromoform was observed along the coasts of tropical islands under a sea breeze. Polybromomethane concentrations were highly correlated among the coastal samples, and the ratios CH 2 Br 2 /CHBr 3 and CHBr 2 Cl/ CHBr 3 showed a clear tendency to decrease with increasing CHBr 3 concentration. These findings are consistent with the observations that polybromomethanes are emitted mostly from macroalgae whose growth is highly localized to coastal areas and that CHBr 3 has the shortest lifetime among these three compounds. The relationship between the concentration ratios CHBr 3 /CH 2 Br 2 and CHBr 2 Cl/CH 2 Br 2 suggested a large mixing/ dilution effect on bromomethane ratios in coastal regions and yielded a rough estimate of 9 for the molar emission ratio of CHBr 3 /CH 2 Br 2 and of 0.7 for that of CHBr 2 Cl/CH 2 Br 2 . Using these ratios and an global emission estimate for CH 2 Br 2 (61 Gg/yr (Br)) calculated from its background concentration, the global emission rates of CHBr 3 and CHBr 2 Cl were calculated to be approximately 820(±310) Gg/yr (Br) and 43(±16) Gg/yr (Br), respectively, assuming that the bromomethanes ratios measured in this study are global representative. The estimated CHBr 3 emission is consistent with that estimated in a very recent study by integrating the sea-to-air flux database. Thus the contribution of CHBr 3 and CHBr 2 Cl to inorganic Br in the atmosphere is likely to be more important than previously thought.

Measurements of NO, NO y , CO and O3 and estimation of the ozone production rate at Oki Island, Japan, during PEM‐West

Measurements of NO, NOy, CO, and O3 were conducted at Oki Island, 65 km west of the Japanese mainland during September–October 1991. The results show that the Oki Island site is relatively clean with mean (and median) CO and NOy concentrations of 137 (130) ppbv and 713 (505) pptv, respectively. These relatively low concentrations reflect the frequent occurrence of windsfrom the less populated regions to the north during this campaign. During several periods, elevated CO, NOy, and O3 concentrations were associated with transport of pollutants from Japan and Korea. CO and NOy are significantly correlated in the entire data set, reflecting the overall influence of anthropogenic emissions. Mean CO and NOy concentrations show small diurnal cycles with a maximum in the morning and early evening hours. Hourly mean O3 concentrations exhibit a diurnal cycle of amplitude 3.5 parts per billion by volume, with a maximum in the early afternoon attributed to photochemical O3 production. The source of this afternoon O3 enhancement is analyzed using regression analysis of O3 and NOy and of O3 and CO. Both NOy and CO are significantly correlated with O3 during the daytime but are poorly or insignificantly correlated with O3 at night, indicating that upwind photochemistry operating within the previous ∼1 day was responsible for the observed afternoon O3 enhancement. The NOy-O3 regression analysis indicates formation of ∼9 O3 molecules per NOy molecule reaching Oki Island. The mean and median midday NO concentrations of 55 and 23 parts per trillion by volume, respectively, were sufficient to support net production of O3. Using the results of these measurements and prior modeling studies (Lin et al., 1988), we estimate a “lifetime-averaged” O3 production efficiency of 10 molecules O3 per NOx molecule. Combined with estimated East Asian NOx emissions for 1987, this indicates an annual O3 production of 1.0 × 1014 g O from photochemistry which is approximately 2 times the annual stratospheric flux in this region. This value must be considered as a rough estimate but is probably accurate to within a factor of 2.

Lead isotope ratios in the urban air of eastern and central Russia

In order to characterize airborne lead in eastern and central Russian cities in terms of lead isotope ratios, aerosol samples were collected at six selected cities and Moscow, and their lead concentrations and isotope ratios were studied by comparing them to the data of ore lead used in Russia. All eastern Russian cities (Vladivostok, Khabarovsk and Yakutsk) were found to have isotope ratios similar to those of ore leads in Kazakhstan, the major lead producer for Russia. Samples collected in Moscow also showed isotope ratios similar to those of eastern Russian cities. The contribution from coal combustion to airborne lead was considered to be small even in winter, in these cities. This observation suggested that the origin of lead in these Russian atmosphere regions is closely related to the lead products (e.g. leaded gasoline). The lead isotope ratios in three eastern Russian cities were very close to the value for Russian air mass reported previously in Japan, which were also in good agreement with the same observation in Sweden. However, considerably different lead isotope ratios were observed in central Russian cities, Kemerovo and Nizhnevartovsk, indicating that specific lead emissions, such as industrial activities using Precambrian-age ores or unique leaded gasoline, might contribute to the atmospheric lead.