Satoshi Sugawara

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.

Fractionation of N2O isotopomers in the stratosphere

The vertical distribution of isotopomers of N2O (14N15N16O, 15N14N16O, and 14N14N18O) in the lower and middle stratosphere was observed over Japan (39°N, 142°E) in 1999 using a balloon-borne cryogenic sampler and ground-based mass spectrometry. The abundance of the heavier isotopomers relative to 14N14N16O increased with altitude, while the mixing ratio of N2O decreased due to photochemical depletion. Maximum fractionation was observed at the highest altitude, 34.5 km, where δ15Nαair (isotopomer ratio of center nitrogen), δ15Nβair (end nitrogen), and δ18OSMOW were 144.l‰, 42.4‰, and 119.0‰, respectively. The observed distribution is mostly accounted for by isotopic fractionation during consumption processes, which is in accordance with reported simulation experiments and theoretical prediction for photolytic fractionation of N2O isotopomers. However, the apparent fractionation factors in the lower (<∼24 km) and higher regions are different, which suggests that (1) the fractionation factor for stratospheric photolysis may depend on altitude or latitude, (2) transport and mixing processes in the stratosphere can affect the vertical profile, and (3) the relative contribution of photolysis and photo-oxidation to total N2O sink is possibly dependent on altitude.

Atmospheric CO2 variations over the last three glacial–interglacial climatic cycles deduced from the Dome Fuji deep ice core, Antarctica using a wet extraction technique

A deep ice core drilled at Dome Fuji, East Antarctica was analyzed for the CO2 concentration using a wet extraction method in order to reconstruct its atmospheric variations over the past 320 kyr, which includes three full glacial—interglacial climatic cycles, with a mean time resolution of about 1.1 kyr. The CO2 concentration values derived for the past 65 kyr are very close to those obtained from other Antarctic ice cores using dry extraction methods, although the wet extraction method is generally thought to be inappropriate for the determination of the CO2 concentration. The comparison between the CO2 and Ca2× concentrations deduced from the Dome Fuji core suggests that calcium carbonate emitted from lands was mostly neutralized in the atmosphere before reaching the central part of Antarctica, or that only a small part of calcium carbonate was involved in CO2 production during the wet extraction process. The CO2 concentration for the past 320 kyr deduced from the Dome Fuji core varies between 190 and 300 ppmv, showing clear glacial—interglacial variations similar to the result of the Vostok ice core. However, for some periods, the concentration values of the Dome Fuji core are higher by up to 20 ppmv than those of the Vostok core. There is no clear indication that such differences are related to variations of chemical components of Ca2×, microparticle and acidity of the Dome Fuji core.

Vertical profile of the carbon isotopic ratio of stratospheric methane over Japan

Stratospheric air samples were collected over Japan on August 31, 1994 using a balloon-borne cryogenic sampler and then analyzed for the CH4 concentration and δ13C in CH4. The δ13C value increased from about −47.5‰ at the tropopause to about −38.9‰ at 34.7 km, accompanied by a rapid decrease of the CH4 concentration with height. From the measured values of the CH4 concentration and δ13C, the apparent carbon isotopic fractionation factor was estimated to be 1.0131±0.0006. The contributions of the chemical CH4 reactions with OH, O(¹D) and Cl were also examined by using an one-dimensional photochemical-diffusion model. It is suggested from this examination that the reaction of CH4 with Cl is especially important for δ13C in the stratosphere.

Measurements of the stratospheric carbon dioxide concentration over Japan using a Balloon-borne cryogenic sampler

Stratospheric air samples have been collected once per year since 1985 over Japan using a balloon-borne cryogenic sampler and then analyzed for their CO2 concentrations. The measurements showed high values of CO2 in the lowest part of the stratosphere, then a decrease with height to 20.0–25.0 km, and almost constant values above this level. From the comparison with the results of our aircraft measurements in the upper troposphere and lower stratosphere, it is suggested that the vertical profile of stratospheric CO2 over Japan is strongly related to transport processes that are associated with tropospheric air being introduced into the stratosphere in the tropical region and then moving poleward with different speeds at different heights. The average rate of the CO2 increase from 1985 to 1991 was estimated to be 1.4 ppmv/year; this is similar to the rate found for the troposphere over the same period.

Aircraft measurements of the stable carbon isotopic ratio of atmospheric methane over Siberia.

Air samples collected using aircraft during the Siberian Terrestrial Ecosystem-Atmosphere-Cryosphere Experiments (STEACE) in the summer of 1993 and 1994 were analyzed for the carbon isotopic ratio, δ13C, of atmospheric CH4 as well as for the CH4 concentration. The CH4 concentrations and δ13C values observed in the lower troposphere over wetlands in the West Siberian Lowland varied considerably, showing a clear negative correlation between the two components. From the relationships between measured values of the CH4 concentration and δ13C, values of δ13C of CH4 released from wetlands into the atmosphere were estimated to be −75 to −67‰. The results observed over oil wells and pipelines showed isotopic evidence for leakage of natural gas. Mean values of δ13C measured in the middle and upper troposphere over Siberia in the summer season were −47.9±0.3 and −47.8±0.2‰ for 1993 and 1994, respectively, which are quite similar to each other.

Improving stratospheric transport trend analysis based on SF6 and CO2 measurements

In this study we reexamine nearly four decades of in situ balloon-based stratospheric observations of SF6 and CO2 with an idealized model and reanalysis products. We use new techniques to account for the spatial and temporal inhomogeneity of the sparse balloon profiles and to calculate stratospheric mean ages of air more consistently from the observations with the idealized model. By doing so we are able to more clearly show and account for the variability of mean age of air throughout the bulk of the depth of the stratosphere. From an idealized model guided by the observations, we identify variability in the mean age due to the seasonal cycle of stratospheric transport, the quasi-biennial oscillation in tropical zonal winds, major volcanic eruptions, and linear trends that vary significantly with altitude. We calculate a negative mean age trend in the lowest 5 km of the stratosphere that agrees within uncertainties with a trend calculated from a set of chemistry climate model mean ages in this layer. The mean age trends reverse sign in the middle and upper stratosphere and are in agreement with a previous positive trend estimate using the same observational data set, although we have substantially reduced the uncertainty on the trend. Our analysis shows that a long time series of in situ profile measurements of trace gases such as SF6 and CO2 can be a unique and useful indicator of stratospheric circulation variability on a range of time scales and an important contributor to help validate the stratospheric portion of global chemistry climate models. However, with only SF6 and CO2 measurements, the competing effects on mean age between mean circulation and mixing (tropical entrainment) are not uniquely separable.

Carbon dioxide variations in the stratosphere over Japan, Scandinavia and Antarctica

Systematic collections of stratospheric air samples have been conducted over Japan since 1985 using a balloon-borne cryogenic sampler. The collection of stratospheric air samples was also carried out twice over Scandinavia and once over Antarctica. Vertical profiles of CO2 concentration thus obtained over these locations were quite similar to each other; CO2 concentration decreased with increasing altitude in the lower stratosphere and reached an almost constant value in the mid-stratosphere. δ13C of stratospheric CO2observed over these locations enriched with increasing altitude. A negative correlation between δ13C and CO2 concentration with Δδ13C/ΔCO2 of −0.02‰ ppmv−1 was found in the lower stratosphere. Although CO2 concentration was almost constant in the mid-stratosphere, the δ13C enrichment was observed in succession. δ18O of stratospheric CO2 also enriched with increasing altitude. The enrichment was significant; δ18O was almost 0‰ at the tropopause and reached a maximum value of about 11‰ at a layer with N2O concentration of about 10 ppbv. A compact relation between δ18O and N2O concentration was consistently observed for these locations. Stratosperic CO2 over Japan showed a secular increase with an average rate of 1.4 ppmv yr−1 for the period 1985–2000. The secular increase was not constant with time, and temporal stagnation of the CO2 increase was observed in 1997.

Concentration variations of tropospheric nitrous oxide over Japan

Aircraft measurements of the tropospheric N2O concentration were made over Japan during the period from October 1991 to June 1999. The observed values of the N2O concentration showed clear evidence of the secular increase, with mean rates of 0.50 to 0.64 ppbv/yr for selected height intervals of 0–2, 2–4, 4–6, 6–8 km and 8 km-tropopause. Although the seasonality of the N2O concentration was hardly observable throughout the troposphere, interannual variations with periods of about 2 years were clearly found. The average N2O concentrations over the observation period for the above 5 height intervals were almost identical with each other, showing no appreciable vertical gradient of the concentration. This suggests that N2O emissions from the ground surface around Japan are very weak and the emitted N2O is mixed well in the troposphere.

Variations of stratospheric trace gases measured using a balloon-borne cryogenic sampler

Abstract For a better understanding of the cycles of atmospheric trace gases, we have continued to systematically collect air samples in the stratosphere over Japan since 1985, using a balloon-borne cryogenic sampler. The collection of the stratospheric air samples was also made twice over the Scandinavian Peninsula in 1997 and once over Japanese Antarctic station, Syowa in 1998. The air samples collected were analyzed not only for the concentrations of CO2, CH4, N2O and various halocarbons but also for their isotopic ratios. These measurements revealed that, in general, the concentrations of all gas components decreased and their isotopic ratios increased with increasing height, due to influence of atmospheric transport and photochemical destruction in the stratosphere. However, detailed inspection of the results indicated that the observed vertical profiles of the respective components were quantitatively different, depending on location and time. Stratospheric CO2 over Japan showed the secular increase with an average rate of 1.4 ppmv/year for the period 1985–1999.