Vertical diffusion in a stable boundary layer near the surface is not clearly understood. In the present study, the vertical diffusivity of radon and the height below which the concentration of radon ...is high are estimated from observations made at two levels (1.5 and 100 m) on the meteorological tower in the campus of the Meteorological Research Institute, Tsukuba, Japan, in November 2006. Seven 12-hour episodes, in which radon concentration near the surface increased, were averaged to make one sequential dataset. The averaged time sequence was divided into two periods: the radon concentration near the surface increased in the first one (Period I) and was stationary in the second (Period II). The estimated vertical diffusivity was less than 0.05 m2 s-1 for Period I and was at most 0.13 m2 s-1 for Period II. The estimated thickness of the radon-rich layer was less than 50 m for the first three hours in the first period; however, inversion height was approximately 100 m. The height under which radon accumulated was somewhat lower than that at the temperature inversion in period I, which suggests that the turbulent transfer was not dominant in the process to generate the temperature inversion layer in this area. Although the vertical diffusion of radon was different between the two periods, it was difficult to distinguish them with surface observation, employed for conventional Pasquill stability categories classification.
Since 1993, atmospheric carbon dioxide (CO2) has been continuously observed by the Japan Meteorological Agency at Minamitorishima station (24°18′N, 153°58′E), located about 2000 km off the Asian ...continent in the western North Pacific. The long‐term record shows high‐frequency measurements with interesting episodic events with extremely low CO2 mixing ratios 5–10 ppm below the background seasonal cycle. These extremely low CO2 (ELC) events occur several times each year, primarily in July, August, and September, although the number of events varies from year to year. The origins of air masses associated with the ELC events were defined by backward trajectory analyses as well as chemical characterizations using simultaneous observations of other trace gases (CO, CH4, and O3). The results indicate that the air masses with extremely low CO2 were influenced by active biospheric uptake in summer over different continental sink regions in Siberia, northern Asia, and Southeast Asia due to rapid long‐range transport driven by strong northerly or southerly winds. The spatial scale of the widespread low‐CO2 distribution for the ELC events in 2001 was captured by a simulation experiment using a three‐dimensional chemical transport model. It clearly revealed that the Intertropical Convergence Zone around 20°N in the western North Pacific during summer blocked further southward intrusion of ELC events through the lower troposphere.
A continuous measuring system for atmospheric O2/N2 ratio was developed employing a paramagnetic oxygen analyzer. Sample air is allowed to flow through a water trap cooled to −80°C, and is introduced ...into the analyzer at a flow rate of 100 mL min−1 by stabilizing the pressure to an order of 10−1 Pa. The analytical reproducibility of the O2/N2 ratio achieved by the system is about 5 and 3 per meg for 2 and 30 minutes average values, respectively. The O2/N2 ratio values obtained by the system are in good agreement with the values obtained by our traditional system using a mass spectrometer. Using our new system, we started measuring the atmospheric O2/N2 ratio at Minamitorishima, Japan since December, 2015. Some preliminary results show clearly the O2/N2 day-to-day and seasonal variations that are in the opposite phase with the CO2 concentration.
Temporal variations of carbon monoxide (CO) were observed simultaneously at seven surface stations located in east Asia/western North Pacific from 24°N to 43°N during the East Asian Regional ...Experiment (EAREX) 2005 campaign in March 2005. Three major pollution events with enhanced CO levels were recorded around the same time at four stations over the East China Sea and at two northern stations of Japan. These pollution events were also observed 3–4 d later at Minamitorishima, located far from the Asian continent. A synoptic weather analysis showed that all of the major CO enhancements were brought about by the passages of cold fronts associated with the eastward migrating cyclonic development. The CO distribution simulated by a three‐dimensional transport model showed that the polluted air masses exported from the continent were trapped behind the cold fronts and then merged into elongated belts of enriched CO before spreading over the western North Pacific. Transport of regionally tagged CO tracer simulated by the model indicated that the Chinese and Korean emissions were the major contributors to the pollution over the East China Sea, while the Japanese emissions had impacts at relatively higher latitude regions during the campaign. The simulation results also showed that the CO enhancements detected at Minamitorishima were caused by a long‐range transport of pollution emissions from various regions in east Asia. The CO‐enriched plumes from Southeast Asia and south Asia emissions were found above the boundary layer in the frontal zone but not at the surface.
A four-dimensional variational method (4D-Var) is a popular technique for source/sink inversions of atmospheric constituents, but it is not without problems. Using an icosahedral grid transport model ...and the 4D-Var method, a new atmospheric greenhouse gas (GHG) inversion system has been developed. The system combines offline forward and adjoint models with a quasi-Newton optimization scheme. The new approach is then used to conduct identical twin experiments to investigate optimal system settings for an atmospheric CO2 inversion problem, and to demonstrate the validity of the new inversion system. In this paper, the inversion problem is simplified by assuming the prior flux errors to be reasonably well known and by designing the prior error correlations with a simple function as a first step. It is found that a system of forward and adjoint models with smaller model errors but with nonlinearity has comparable optimization performance to that of another system that conserves linearity with an exact adjoint relationship. Furthermore, the effectiveness of the prior error correlations is demonstrated, as the global error is reduced by about 15 % by adding prior error correlations that are simply designed when 65 weekly flask sampling observations at ground-based stations are used. With the optimal setting, the new inversion system successfully reproduces the spatiotemporal variations of the surface fluxes, from regional (such as biomass burning) to global scales. The optimization algorithm introduced in the new system does not require decomposition of a matrix that establishes the correlation among the prior flux errors. This enables us to design the prior error covariance matrix more freely.
Continuous observations of atmospheric δ(O2/N2) and CO2 amount fractions have been carried out at Ryori (RYO), Japan, since August 2017. In these observations, the O2 : CO2 exchange ratio (ER, ...-Δy(O2)Δy(CO2)-1) has frequently been lower than expected from short-term variations in emissions from terrestrial biospheric activities and combustion of liquid, gas, and solid fuels. This finding suggests a substantial effect of CO2 emissions from a cement plant located about 6 km northwest of RYO. To evaluate this effect quantitatively, we simulated CO2 amount fractions in the area around RYO by using a fine-scale atmospheric transport model that incorporated CO2 fluxes from terrestrial biospheric activities, fossil fuel combustion, and cement production. The simulated CO2 amount fractions were converted to O2 amount fractions by using the respective ER values of 1.1, 1.4, and 0 for the terrestrial biospheric activities, fossil fuel combustion, and cement production. Thus obtained O2 and CO2 amount fraction changes were used to derive a simulated ER for comparison with the observed ER. To extract the contribution of CO2 emissions from the cement plant, we used y(CO2∗) as an indicator variable, where y(CO2∗) is a conservative variable for terrestrial biospheric activities and fossil fuel combustion obtained by simultaneous analysis of observed δ(O2/N2) and CO2 amount fractions and simulated ERs. We confirmed that the observed and simulated ER values and also the y(CO2∗) values and simulated CO2 amount fractions due only to cement production were generally consistent. These results suggest that combined measurements of δ(O2/N2) and CO2 amount fractions will be useful for evaluating CO2 capture from flue gas at carbon capture and storage (CCS) plants, which, similar to a cement plant, change CO2 amount fractions without changing O2 values, although CCS plants differ from cement plants in the direction of CO2 exchange with the atmosphere.
Continuous observations of atmospheric ð³(O2/N2) and CO.sub.2 amount fractions have been carried out at Ryori (RYO), Japan, since August 2017. In these observations, the O.sub.2 Çë:ÇëCO.sub.2 ...exchange ratio (ER, -ðöy(O2)ðöy(CO2)-1) has frequently been lower than expected from short-term variations in emissions from terrestrial biospheric activities and combustion of liquid, gas, and solid fuels. This finding suggests a substantial effect of CO.sub.2 emissions from a cement plant located about 6Çëkm northwest of RYO. To evaluate this effect quantitatively, we simulated CO.sub.2 amount fractions in the area around RYO by using a fine-scale atmospheric transport model that incorporated CO.sub.2 fluxes from terrestrial biospheric activities, fossil fuel combustion, and cement production. The simulated CO.sub.2 amount fractions were converted to O.sub.2 amount fractions by using the respective ER values of 1.1, 1.4, and 0 for the terrestrial biospheric activities, fossil fuel combustion, and cement production. Thus obtained O.sub.2 and CO.sub.2 amount fraction changes were used to derive a simulated ER for comparison with the observed ER. To extract the contribution of CO.sub.2 emissions from the cement plant, we used y(CO2êù) as an indicator variable, where y(CO2êù) is a conservative variable for terrestrial biospheric activities and fossil fuel combustion obtained by simultaneous analysis of observed ð³(O2/N2) and CO.sub.2 amount fractions and simulated ERs. We confirmed that the observed and simulated ER values and also the y(CO2êù) values and simulated CO.sub.2 amount fractions due only to cement production were generally consistent. These results suggest that combined measurements of ð³(O2/N2) and CO.sub.2 amount fractions will be useful for evaluating CO.sub.2 capture from flue gas at carbon capture and storage (CCS) plants, which, similar to a cement plant, change CO.sub.2 amount fractions without changing O.sub.2 values, although CCS plants differ from cement plants in the direction of CO.sub.2 exchange with the atmosphere.
A new automated 222Rn measuring system suitable for a wide range of atmospheric observations has been developed. This system comprises a 222Rn analyzer and an air-sampling unit, along with a pump, ...drying equipment, and a filter. The operation of this 222Rn analyzer is based on an electrostatic collection method involving the use of a PIN photodiode to separately detect a particles emitted from 218Po and 214Po released from the decay of 222Rn in a hemispheric air-sample chamber. The response of the 222Rn analyzer with respect to the applied voltage, chamber volume size, and sample flow rate is investigated to determine the appropriate measuring conditions. With this instrument, the detection limits have improved to 0.16-0.20 Bq m-3 for 1 h. The new 222Rn analyzer shows several technical advancements over the previous electrostatic collection methods, such as an improved detection limit, higher sensitivity, higher time-resolution analysis, and longer life. During the preliminary observational test, the 222Rn measuring system was able to detect the diurnal cycle in 222Rn resulting from the mixing of rapid vertical air in the surface boundary layer. At the Minamitorishima station located far from the continent, very small 222Rn peaks were clearly detected when long-range transport of polluted air masses from the Asian continent was observed at the station. We demonstrate that our compact 222Rn measuring system has the potential to be widely used for high time-resolution measurements of low-level 222Rn.
Aircraft observations and numerical simulations using an atmospheric transport model exhibit large latitudinal gradients in the carbon dioxide (CO2) mixing ratio around the subtropics and equator ...throughout the troposphere. The formation mechanisms of the latitudinal CO2 gradients are investigated at aircraft flight altitudes (350–260 hPa) by considering the influences of atmospheric transport and carbon fluxes at the earth's surface. A meridional transport analysis demonstrates how various transport processes create the latitudinal CO2 gradients in the upper troposphere. The analysis result shows that around the northern subtropics, the suppression of meridional mixing sharpens the CO2 gradient during boreal winter and spring. In other words, extratropical cyclonic activity effectively flattens the mixing ratio along isentropic surfaces at midlatitudes and induces gradients around the subtropics. The southern subtropical CO2 gradient is also induced by the subtropical mixing barrier and convergence of the cross‐equatorial eddy flux. Different from the subtropical gradients, a CO2 gradient in the tropical upper troposphere is not created by the suppression of meridional transport but is created by the uplifting of low‐level air during boreal winter and spring. The latitudinal CO2 gradient in the tropical upper troposphere decreases due to interhemispheric transport. The seasonal migration of the mean Hadley circulation yields efficient interhemispheric transport and reduces the tropical CO2 gradient.
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