A New Compact Cryogenic Air Sampler and Its Application in Stratospheric Greenhouse Gas Observation at Syowa Station, Antarctica

Shinji Morimoto National Institute of Polar Research, Tokyo, Japan

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Takashi Yamanouchi National Institute of Polar Research, Tokyo, Japan

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Hideyuki Honda Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Sagamihara, Japan

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Issei Iijima Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Sagamihara, Japan

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Tetsuya Yoshida Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Sagamihara, Japan

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Shuji Aoki Tohoku University, Sendai, Japan

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Takakiyo Nakazawa Tohoku University, Sendai, Japan

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Shigeyuki Ishidoya Tohoku University, Sendai, Japan

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Satoshi Sugawara Miyagi University of Education, Sendai, Japan

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Abstract

To collect stratospheric air samples for greenhouse gas measurements, a compact cryogenic air sampler has been developed using a cooling device called the Joule–Thomson (J–T) minicooler. The J–T minicooler can produce liquefied neon within 5 s from high pressure neon gas precooled by liquid nitrogen. The sampler employs liquid neon as a refrigerant to solidify or liquefy sampled atmospheric constituents. Laboratory experiments showed that the sampler is capable of collecting about 3 and more than 7 L STP of air at 25 and 120 hPa, respectively, which corresponds to about 25 and 15 km above ground within 240 s, respectively. The new balloon-borne sampling system, which was set up for Antarctic experiments, consists of the compact sampler, a 2-L high pressure neon gas cylinder, pneumatic and solenoid valves, a controller with a GPS receiver, a telemetry transmitter, and batteries. The size of the sampling system is 300 mm width × 300 mm depth × 950 mm height and it weighs about 22 kg (including liquid nitrogen). Two of these compact sampling systems (configured for sampling at altitudes 18 and 25 km) were launched from Syowa Station (69.0°S, 39.5°E), Antarctica, in January 2008 using 1000 or 2000 m3 plastic balloons. They were launched successfully and recovered without any problem on sea ice on the same day as their launch. The collected stratospheric air samples showed reasonable concentrations of the stratospheric greenhouse gases over the Antarctic region.

Corresponding author address: Shinji Morimoto, National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan. Email: mon@nipr.ac.jp

Abstract

To collect stratospheric air samples for greenhouse gas measurements, a compact cryogenic air sampler has been developed using a cooling device called the Joule–Thomson (J–T) minicooler. The J–T minicooler can produce liquefied neon within 5 s from high pressure neon gas precooled by liquid nitrogen. The sampler employs liquid neon as a refrigerant to solidify or liquefy sampled atmospheric constituents. Laboratory experiments showed that the sampler is capable of collecting about 3 and more than 7 L STP of air at 25 and 120 hPa, respectively, which corresponds to about 25 and 15 km above ground within 240 s, respectively. The new balloon-borne sampling system, which was set up for Antarctic experiments, consists of the compact sampler, a 2-L high pressure neon gas cylinder, pneumatic and solenoid valves, a controller with a GPS receiver, a telemetry transmitter, and batteries. The size of the sampling system is 300 mm width × 300 mm depth × 950 mm height and it weighs about 22 kg (including liquid nitrogen). Two of these compact sampling systems (configured for sampling at altitudes 18 and 25 km) were launched from Syowa Station (69.0°S, 39.5°E), Antarctica, in January 2008 using 1000 or 2000 m3 plastic balloons. They were launched successfully and recovered without any problem on sea ice on the same day as their launch. The collected stratospheric air samples showed reasonable concentrations of the stratospheric greenhouse gases over the Antarctic region.

Corresponding author address: Shinji Morimoto, National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan. Email: mon@nipr.ac.jp

1. Introduction

To delineate the temporal and spatial variations of greenhouse gases in the troposphere and to elucidate sources of the variations, a large number of observations have been carried out around the world using surface stations, aircraft, and ships (e.g., WMO 2008). We have also carried out continuous measurements of atmospheric CO2 and CH4 concentrations at Syowa Station (69.0°S, 39.5°E), Antarctica, since 1984 and 1988, respectively (Aoki et al. 1992; Morimoto et al. 2003). Variations of stratospheric greenhouse gases, both in time and space, have also been observed by using balloon-borne and airborne in situ instruments and/or a cryogenic whole air sampler (e.g., Bischof et al. 1985; Schmidt and Khedim 1991; Boering et al. 1995; Aoki et al. 2003). In recent years, the horizontal and vertical distributions of stratospheric CO2 and SF6 concentrations were investigated as a proxy measure for the “age” of the stratospheric air, based on the fact that both of these gases have been increasing linearly with time in the troposphere and are quite stable in the stratosphere after being transported mainly from the tropical tropopause (e.g., Andrews et al. 2001; Engel et al. 2009). Secular increase of the stratospheric CH4 concentration was detected by Rohs et al. (2006). They also estimated the contribution of CH4 to water vapor increase observed in the stratosphere by using balloon-borne CH4, H2, and N2O data. For further understanding of the temporal and spatial variations of stratospheric greenhouse gases, more frequent observations at more locations are needed, necessitating a requirement for a more convenient instrumentation than the ones that exist now.

A balloon-borne cryogenic whole air sampler has certain advantages for studying greenhouse gases in the stratosphere; one of which is the physical recovery of air samples that can then be analyzed in laboratories with optimal precisions for concentrations (Nakazawa et al. 1995) and isotopes (Sugawara et al. 1997; Toyoda et al. 2004). However, the existing cryogenic samplers employ large amounts of liquid helium or liquid neon as an onboard refrigerant, so these are heavy and large (e.g., Schmidt et al. 1987; Honda et al. 1996a). As a result, extensive operations with a large number of experienced personnel are required for ground preparation, launching, and recovery of a large balloon-borne cryogenic air sampling system. To rectify some of these issues, a more portable sampling system that can be easily handled with minimum personnel is needed.

We have developed a compact cryogenic air sampler, named the Joule–Thomson (J–T) sampler, using a J–T minicooler, liquid nitrogen, and high pressure neon gas. With the J–T cooler, liquid neon can be produced from pressurized neon gas precooled by liquid nitrogen; the liquescence lasts for about 300 s when using neon gas contained in a 2-L high pressure cylinder at a pressure of 19.0 MPa. The J–T sampler uses liquid neon (produced in situ) as refrigerant to solidify or liquefy all of the atmospheric constituents except for helium, hydrogen, and neon. In this paper, we present a description of our newly developed J–T sampler and some preliminary results from the stratospheric air sampling experiments using the J–T sampler conducted at Syowa Station, Antarctica, in January 2008.

2. Compact cryogenic air sampler with a J–T minicooler

a. J–T minicooler

The J–T minicooler is one of the typical devices producing low temperatures for cooling infrared sensors, electronic devices, etc., by adiabatic expansion of a high pressure gas into the atmosphere through a throttling orifice (Ng et al. 2002), which is known as the Joule–Thomson effect. A schematic diagram showing a characteristic size of the J–T minicooler used in this study (Taiyo Nippon Sanso NCS-3) is displayed in Fig. 1. The J–T minicooler, consisting of a finned capillary for supplying high pressure gas and a 0.12-mm expansion orifice where low temperature is produced, is inserted into a sheath tube (also shown in Fig. 1); the tube on the orifice side is closed. Because the incoming high pressure and high temperature gas flowing in the finned capillary is precooled by a counter flow of the low temperature gas expanded at the orifice, a short cooling-down time is easily attained. The cooling power Q (in watts) produced by the J–T minicooler is given by
i1520-0426-26-10-2182-e1
where m(g s−1) denotes the mass flow rate, and H0 and H1(J g−1) are the enthalpies of the supplied high pressure gas and exhausted low pressure gas, respectively. When H1 is larger than H0 for a supplied gas, the J–T minicooler is capable of cooling the gas down to its freezing temperature.

For collecting atmospheric constituents cryogenically, we selected neon gas of 99.999% purity (Taiyo Nippon Sanso) as a working gas for the J–T minicooler. Because the Joule–Thomson inversion temperature for neon at a pressure of 20 MPa is around 180 K, the neon gas needed to be precooled to temperatures below 180 K before being introduced into the J–T minicooler. We employed liquid nitrogen (LN2; 78 K at 1 atm) as a coolant for precooling the supplied neon gas. It should be noted that the enthalpy difference of the neon gas (H1H0) showed a maximum value at a temperature around 75 K (with gas pressure at 20 MPa), indicating that an optimal cooling power of the J–T minicooler can be attained with the neon gas at the LN2 temperature. The liquefied neon, produced by the J–T minicooler, can liquefy or solidify all of the atmospheric constituents except for helium, hydrogen, and neon (Lueb et al. 1975).

To examine the cooling power produced by the J–T minicooler, we measured the heat input to the J–T minicooler that is required for balancing the cooling power. In the experiment, a direct current (dc) heater was attached to the closed end of the sheath tube (cf. Fig. 1) as a heat input and an AuFe/Cr thermocouple for temperature measurement at the expansion orifice of the J–T cooler. As the LN2-precooled neon gas was introduced into the J–T minicooler and liquefied, the dc voltage to the heater was increased until the temperature started to rise; at this point, the heat input power was equal to the cooling power of the J–T minicooler. The neon gas was supplied from a 47-L cylinder to the J–T minicooler, pushed through a 1/8-in. outside diameter (OD) × 2-m-long copper tube dipped into LN2 for precooling. No pressure regulation was applied along the gas flow, with the J–T cooler receiving pressure directly from the cylinder; the neon gas exhausted from the cooler was released into the atmosphere. From this procedure, the cooling power was determined to be 23.6 W at the neon gas pressure of 13.9 MPa and decreased almost linearly with decreasing pressure. Finally, no cooling power was observed at the neon gas pressure of 5.0 MPa.

Figure 2 shows temperature change with time of the neon gas after expansion at the orifice of the J–T minicooler for four different initial pressures of the neon gas (17.0, 11.0, 7.6, and 6.7 MPa). These data were obtained using the same equipment as above but with no heater. For the initial pressures >7.6 MPa, the figure shows that the temperature of the gas decreased to 27 K and liquefied within 4 s.

b. Compact cryogenic air sampler (J–T sampler)

Figure 3 shows a cross section of the J–T sampler. The J–T minicooler, the sheath tube, and a cryo-fin are integrated into an 800-mL vessel made by SUS304. The cryo-fin, where the air sample is either liquefied or solidified, is attached to the closed end of the sheath tube. The sample vessel, a 1/2-in. OD SUS tube with a pneumatic close-off valve (Fujikin FPr-71–9.52) for sample inlet and a 1/8-in. OD × 2-m-long copper tube for neon gas precooling, is fitted to the cover of a vacuum-tight flange with a 1-in. OD, 120-mm-long SUS tube. The neon gas expanded at the J–T cooler is released through the 1-in. SUS tube. Another port with a metal-sealed bellows valve (Swagelok SS-4H) is also mounted on the cover for evacuating the vacuum-insulation vessel described below. In addition, four ports are mounted on the flange cover; these ports are used for LN2 and neon gas supply, evaporated nitrogen release, and LN2 exhaust after air sampling is completed. Finally, all the parts are placed into a stainless steel LN2 dewar of 240-mm OD × 330 mm height (Taiyo Nippon Sanso D6000) to which a vacuum-tight flange is welded. For insulating the sample vessel and precooling the introduced neon gas, the dewar is filled with liquid nitrogen. Incoming air sample is also cooled by passing through the 1/2-in. SUS tube before arriving at the cryo-fin. To prevent the solidified or liquefied air sample at the cryo-fin from dropping down to the inner wall of the flask and evaporating again, the cryo-fin is surrounded by a vacuum-insulated vessel. This is because the temperatures of all the parts, except for the cryo-fin and inner wall of the insulation vessel, are higher than the liquefied neon temperature.

Performance of the J–T sampler was examined in our laboratory by sampling low pressure air from 25 to 120 hPa produced in a 40-L vacuum chamber. A schematic diagram of the setup is shown in Fig. 4. The pressure in the chamber was maintained by continuous evacuation with a rotary pump and a CO2/CH4-in-air standard gas supply (used as a sample gas) from a 47-L cylinder. A pressure switch on the chamber controlled the incoming gas flow through a solenoid valve. Because the pressure switch had a hysteresis response to pressure changes, the chamber pressure showed a saw-toothed variation with a peak-to-peak amplitude of 8–10 hPa. Also fitted to the chamber were a pressure sensor (MKS 690A) and a mass flowmeter (Teledyne HS-50KS) to monitor the pressure in the chamber and air sampling rate by the J–T sampler, respectively.

The experimental procedures were as follows: 1) After evacuation of the sample vessel down to an order of 10−4 Pa with a turbomolecular pump, LN2 was introduced into the sampler; 2) waited for approximately 4 h, until the temperature at the cryo-fin reached below 80 K; 3) adjusted the pressure switch to set the inner pressure of the vacuum chamber to a selected value between 25 and 120 hPa; 4) opened neon gas valve to start cooling the cryo-fin and waited for 30 s; 5) opened the air sampling valve for 240 s; and 6) closed the valves for neon and air sampling. The neon gas was supplied from a 2-L cylinder at 19.0 MPa without pressure regulation. The neon gas pressure in the cylinder decreased to approximately 7.0–9.0 MPa after supplying to the J–T sampler for 270 s. The terminal pressure depended on the conductance of the neon gas at the orifice and/or the counterflow heat exchanger of the J–T minicooler. After the air sampling was completed, the sampling vessel was removed from LN2 and left in ambient atmosphere until the vessel’s temperature returned to room temperature. The inner pressure of the vessel was then measured to calculate the sample amount collected by the J–T sampler.

Figure 5 shows a time series of the air sampling rate and the neon gas pressure supplied to the J–T sampler when the air sample pressure in the chamber was set to 60 hPa. The sampling rate was over 3.0 standard liters per minute (SLM) when the neon gas pressure was 15.1 MPa and decreased to 0.5 SLM with the neon pressure decreasing to 7.2 MPa. The air sampling rate showed fluctuations corresponding to the saw-toothed variations of the chamber pressure, as noted above. In the experiment, an air sample of 5.8 LSTP was collected in 4 min using a total of 190 LSTP neon gas and 0.25 L of LN2. The nitrogen gas evaporating from LN2 during the precooling of both the introduced neon gas and incoming air sample was released to the atmosphere without pressure control. The relationship between the sample pressure and the collected sample amount was examined by repeating the air sampling experiment with sample pressures of 25, 60, and 120 hPa, corresponding roughly to atmospheric altitudes of 25, 20, and 15 km, respectively. The results are shown in Fig. 6. The sample amount collected in 240 s was around 7.2 LSTP at the air sample pressure of 120 hPa and decreased to 3.1 LSTP at 25 hPa.

Because the triple point pressure of nitrogen is 95 hPa, which corresponds to the atmospheric pressure at an altitude of approximately 16 km, LN2 in the dewer would solidify over the altitude range of a balloon flight. To prevent the LN2 solidification, a check valve (Circle Seals K220–2PP-15) with a cracking pressure of 15 psi (0.1 MPa) was added to the nitrogen gas exhaust ports. By means of pressure control, the pressure of LN2 in the dewer could be kept around 1 atm at an altitude of 25 km. The air sampling experiments carried out in the laboratory with the check valve fitted for the LN2 pressure control resulted in pressure in the LN2 dewer 0.1 MPa higher than ambient pressure. The results are also shown in Fig. 6. As seen in Fig. 6, the collected sample amounts at the sample pressure of 60 hPa were 5.2 ± 0.4 LSTP, which is 12% less than the amount collected when the LN2 pressure was 1 atm. Because LN2 temperature increases with increasing pressure, the cooling power decreases with increasing temperature of the incoming neon gas, as expressed in the temperature dependency of the enthalpy [H0 in Eq. (1)] of neon. Because of the reduced cooling power, the collected sample amount therefore decreases when the LN2 pressure is controlled by the check valve. To mitigate such a reduction of the cooling power, we are planning to lower the cracking pressure of the check valve to about 0.05 MPa for the next version of the sampler. However, for analyzing concentrations and stable isotope ratios of greenhouse gases (CO2, CH4, N2O, and SF6), isotope ratios of O2 and N2, and atmospheric oxygen concentration [δ(O2/N2)] in our laboratories, only 2.2 LSTP of air sample is required (Aoki et al. 2003; Ishidoya et al. 2003; Toyoda et al. 2004). Therefore, even with the cooling rate reduction by increasing the LN2 pressure, the J–T sampler can collect sufficient air sample amounts for various analyses up to 25-km altitude.

To validate the quality of the air samples collected by the J–T sampler, the CO2 and CH4 concentrations and stable carbon isotope ratio of CH4 of the samples (from the CO2/CH4-in-air standard gas) collected in the laboratory experiments were analyzed by using a nondispersive infrared analyzer (NDIR), a gas chromatograph with flame ionization detector (GC/FID), and a GC-combustion mass spectrometer with precisions of 0.1 ppmv, 1 ppbv, and 0.06‰, respectively (Tanaka et al. 1983; Aoki et al. 1992; Morimoto et al. 2006). It was confirmed that the CO2 and CH4 concentrations and the stable carbon isotope ratio of the samples agreed, to within our measurement precision, with the values determined for the CO2/CH4-in-air standard gas from which the samples were obtained. We did not make a similar sampling test for N2O; however, because its physical properties are very similar to those of CO2 and the solidification temperature of N2O is much higher than that of CH4, the N2O concentration in the air sample collected by the J–T sampler ought to be maintained. To reduce sample deterioration risk during its storage in the J–T sampler, the inner wall of the sample vessel was electropolished before use. After this treatment, the degree of sample deterioration was investigated by filling a CO2-in-air standard gas into the J–T sampler at an absolute pressure of 0.6 MPa, corresponding to 5.6 LSTP, and analyzing it after 30 days of storage. The CO2 concentration change was found to be less than 0.2 ppmv, which is similar to our former cryogenic sampler using liquid helium (Honda et al. 1996a). However, if the period of storage is more than one month, corresponding to the case of balloon experiments at Syowa Station (described in section 3), the deterioration of the sample CO2 is likely nonnegligible so that the measured CO2 concentration values should be corrected. For a more precise determination of the CO2 concentration, further treatment of the inner wall of the sample vessel is required. With respect to CH4 and N2O, we had confirmed from the observations at Ny-Ålesund (78.9°N, 11.9°E), Svalbard, and over Japan that the storage of air samples in electropolished vessels has a negligibly small influence on their concentrations and isotope ratios (Ishijima et al. 2001; Morimoto et al. 2006).

c. Compact cryogenic sampling system for balloon experiments

The compact cryogenic sampling system assembled in an aluminum-frame gondola for the balloon experiment is shown in Fig. 7. The sampling system consists of the J–T sampler, a 2-L high pressure cylinder made of fiber-reinforced plastic (FRP; Asahi Seisakusho 212C) with a pneumatic high pressure valve (Neriki DS-3H), two solenoid valves (CKD USG-3–6-1) with a 100-mL gas bottle, a solenoid valve (ASCO model 8263) for the LN2 exhaust, a pressure switch, batteries, and control electronics. A description of the onboard control electronics is given in the next section. The FRP cylinder and the 100-mL gas bottle contain neon and nitrogen gases at 19.0 MPa, respectively. A check valve (Circle Seals 264–4PP-0.1) with a cracking pressure of 0.1 psi (7 hPa) is fitted to the neon gas release port on the J–T sampler to avoid water vapor condensation on the J–T minicooler. The neon and nitrogen gases released from the check valves are diverted to the bottom of the gondola with 1–1/2-in. bellow and 1/4-in. OD copper tubes, respectively. This configuration avoids contamination of air samples, because 1) air sampling is performed during balloon ascent and 2) the sampling intake is located at the top of the sampler. In this connection, it is worth noting that our balloon experiments using a cryogenic sampler with liquid helium (Honda et al. 1996a) showed that an outgassing from the balloon has a negligible influence on air sample quality even if air sampling is made during the balloon ascent (Nakazawa et al. 2002). The pneumatic valves at the air sampling port and the neon gas cylinder are actuated by the nitrogen gas at a pressure of 0.6 MPa supplied from the 100-mL bottle through a small pressure regulator (NTG NR-18) via the solenoid valves. The pressure switch configured to turn on at 800 hPa is installed as an interlock; when the pressure switch is off at the ground, the valves do not work.

To protect the sampling system from landing impact on sea ice, a shock absorber is added to its bottom. The shock absorber is made of crushable paper honeycomb designed to reduce the vertical impact to less than 10 G when the payload weight and descending speed are 25 kg and 7 m s−1, respectively. No contaminant outgassed from the honeycomb can reach the air sampling port.

To avoid excessive drops in temperatures of the valves, batteries, and control electronics while in the stratosphere, these parts are wrapped in thermal insulators and the gaps inside the frame seen in Fig. 7 are filled with styrene foam. In addition, thermofoil heaters (Minco HK51) are attached to the solenoid and pneumatic valves to maintain their temperatures above −20°C. The reason for this is that these valves use O-rings made from nitrile or ethylene propylene diene M-class (EPDM) rubber for sealing and that the nitrogen gas for actuating pneumatic valves will leak out at temperatures below −20°C.

The total size and weight of the sampling system are 300 mm width × 300 mm depth × 950 mm height and 22 kg, respectively, including the shock absorber and the 4.5 L of liquid nitrogen in the J–T sampler.

d. Control electronics and telemetry system

Because the hardware of the onboard control electronics and telemetry system has already been described in detail by Honda et al. (1996b), only a brief explanation is given here.

The onboard controller has four channels for photo-MOS relay to open/close three solenoid valves and to activate a balloon cutter, following a sequence programmed in an EPROM. A GPS receiver (Sony IPS-5000U) is installed to obtain position and altitude of the sampler system. One digital input port is provided for ascertaining the pressure switch status. In addition, information related to the position of the sampling system and the valve status is continuously transmitted to the ground station using an onboard 0.5-W FM transmitter. The system functions automatically throughout the duration of a balloon flight after launch, so that no telecommand system is required. When the GPS altitude exceeds a programmed sampling altitude, the controller initiates the following sequence of sampling protocol: 1) open the neon gas valve to introduce neon gas to the J–T minicooler for 30 s; 2) open the air sampling valve while continuing the neon gas introduction for 240 s; 3) close both valves; and 4) activate the balloon cutter to separate the balloon from the sampler, allowing the sampler system to descend with a parachute. If the sampler system ascends at a nominal speed of 300 m min−1, the vertical resolution of the collected air samples will be 1.2 km. During the descending stage, the remaining LN2 in the J–T sampler is siphoned off to the atmosphere for a safe recovery of the sampler.

To monitor the operational status and position of the sampler, a simple tracking and data receiving system is set up. The tracking system calculates the azimuth and elevation angles of the balloon from the ground station using the GPS data transmitted from the J–T sampler. The system automatically drives a 15-element Yagi antenna toward the balloon using the calculated angles. The GPS and status data are also sent to a PC for displaying the information.

As a back-up device for the balloon tracking, a GPS sonde (Vaisala RS-92) is attached beneath the sampler system. To track the signal from the GPS sonde, we have constructed an additional data receiving system (Vaisala NW21).

3. Balloon-borne stratospheric air sampling experiment at Syowa Station

Stratospheric air sampling experiments using the compact cryogenic sampler system described above were conducted at Syowa Station (69.0°S, 39.5°E), Antarctica, in January 2008 as a part of the overall scientific program of the 49th Japanese Antarctic Research Expedition (JARE). Information related to the payloads and balloons used in the experiments is summarized in Table 1. An analog datalogger was added to sampler B for archiving valve temperatures and battery voltage, so that the sampler B payload was slightly heavier than the sampler A payload. The preprogrammed air sampling altitudes were 25 and 18 km for samplers A and B, respectively.

Because the location of the compact J–T sampler cannot be remotely controlled, its landing position must be predicted prior to balloon launch for safe and reliable recovery with a helicopter. To achieve this, we calculated the expected balloon trajectories using upper-air wind data observed at Syowa Station every 12 h, as well as using balloon trajectory forecasts provided by the University of Wyoming (available online at http://weather.uwyo.edu/polar/balloon_traj.html/). To prevent the J–T sampler from landing on crevasse areas along the coast of the Antarctic continent, we launched the balloon when the meteorological conditions indicated that the sampler would land on the stable fast ice south or west of Syowa Station for a safe recovery.

On 4 January 2008, the compact sampler systems were launched from Syowa Station. Because of the use of small balloons with a free lift of ∼10 kg, the balloon launching operations were carried out by only seven people without heavy vehicles. The two sampler systems were launched sequentially on the same day, with the second sampler being released immediately after the first one landed on the ground. Each sampler system ascended at a nominal speed of 300 m min−1 to the preprogrammed air sampling altitude and descended with parachute after the sampling was finished. The balloon flights lasted for 110 and 92 min for samplers A and B, respectively. It was confirmed by the telemetry signal received at the ground station that the air sampling sequence worked flawlessly as programmed and the two sampler systems landed on stable fast ice. The trajectories of the sampler systems are shown in Fig. 8. The sampler systems were successfully recovered by using helicopters on the same day as their launches. The shock absorber completely protected the sampler system from the landing impact against the ice.

After the sampler systems arrived in Japan in April 2008, the sample amounts in samplers A and B were measured manometrically. As a result, we found that samplers A and B had collected air samples of 2.4 and 5.0 LSTP at 25-km (24.6–25.8) and 18-km (18.1–19.4) altitudes, where the atmospheric pressures were around 26 and 65 hPa, respectively. The sample amounts collected over Syowa Station are also plotted on Fig. 6. The collected amounts were approximately 27% less than those obtained in the laboratory experiments. The difference could be partly ascribed to the fact that the LN2 temperature for precooling the neon gas was higher than 78 K, as described in section 2b. In addition, the neon gas pressure decrease in the 2-L cylinder resulting from low temperatures in the upper troposphere and stratosphere could affect the air sampling rate of the sampler system. Unfortunately, the temperature of the cylinder was not recorded during each of the balloon ascents. However, if the cylinder temperature fell to −40°C, the observed temperature at 18 km over Syowa Station on 4 January 2008, the neon gas pressure would have decreased to around 15.0 MPa from its initial pressure of 19.0 MPa at room temperature. On account of the pressure dependency of enthalpy and flow rate of neon gas—H0 and m in Eq. (1), respectively—the cooling power of the J–T minicooler at 15.0 MPa would have been 60% of the cooling power at 19.0 MPa. This is qualitatively consistent with the results obtained from the Antarctic experiments.

The air samples collected in the stratosphere over Syowa Station on 4 January 2008 were analyzed for concentrations of CO2, CH4, N2O, and SF6; stable isotope ratios of CO2, CH4, N2O, N2, and O2; and O2/N2 ratios at Tohoku University and Tokyo Institute of Technology. Details of the analytical procedures have been given elsewhere (Tanaka et al. 1983; Aoki et al. 1992; Nakazawa et al. 1993; Toyoda and Yoshida 1999; Ishijima et al. 2001; Ishidoya et al. 2003; Morimoto et al. 2006). Because detailed analyses of these data are beyond scope of this paper, only a part of the preliminary results will be presented here.

The concentrations of CH4 and N2O obtained from the balloon flights are plotted against their sampled altitudes in Figs. 9a,b, respectively. Also shown in Figs. 9a,b are the concentrations that were obtained by our previous balloon experiments over Syowa Station in 1998 and 2003 (Nakazawa et al. 2002). CH4 and N2O show similar vertical profiles as the previous data; they decrease rapidly with increasing height, because 1) their chemical destruction rates increase with height and 2) the age of the upper stratospheric air, after leaving the troposphere, is older than the lower stratospheric air. We also note that CH4 and N2O at 18 km in 2008 are lower than in the previous years, resulting in decreased vertical concentration gradients. Such variability could be caused by dynamical processes in the stratosphere. Some previous studies have reported that the vertical profiles of CH4 and N2O have shown large interannual variations in the stratosphere over Japan (Nakazawa et al. 2002).

Evidence in the literature (e.g., Rohs et al. 2006) shows that CH4 and N2O in the stratosphere have a remarkably tight linear relationship for an N2O concentration higher than 70–120 ppbv. Figure 9c shows the relationship between CH4 and N2O observed over Syowa Station in 1998, 2003, and 2008. Also shown is a fitted linear line to the 1998 and 2003 data for N2O concentration larger than 120 ppbv. In Fig. 9c CH4 and N2O concentrations obtained in 2008 fall almost right on the fitted line. These results indicate that the air samples collected by the compact sampler show reasonable greenhouse gas concentration values in stratospheric air over Antarctica.

4. Concluding remarks

We have developed a compact cryogenic air sampler by using a J–T minicooler and high pressure neon gas for collecting stratospheric air samples. A total of two samplers were launched from Syowa Station, Antarctica, using small-sized plastic balloons. They functioned according to design and collected stratospheric air samples successfully on 4 January 2008. Samples were analyzed for concentrations and isotope ratios of various trace gases. Preliminary results show consistency with previous observations, such as vertical concentration gradients of such greenhouse gases as CH4 and N2O. Also, our measurements are consistent with the linear relationship between stratospheric CH4 and N2O obtained in previous observations.

In our new sampling system, liquefied helium or neon is not required as a cooling agent, thus reducing its total weight to around 22 kg. Because of its reduced weight and size, only a small group (in our case, seven people at Syowa Station) is required to carry out the ballooning operation. This makes the employment of our system for sampling stratospheric air from remote locations practical and viable. Compared to the more cumbersome samplers used by previous investigators, the relative ease with which our compact cryogenic sampler system can be deployed will hopefully make our instrument a vital component in future observational studies to delineate more clearly the temporal and spatial variations of the greenhouse gases in the stratosphere. However, to observe vertical profiles of the stratospheric greenhouse gases with a lower cost, our sampling system needs be further improved and modified so that a single small balloon can lift 2 or 3 samplers to the stratosphere.

Acknowledgments

We are grateful to the members of the 48th and 49th Japanese Antarctic Research Expedition for their cooperation in our balloon experiments at Syowa Station. This work was partly supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan, Grants-in-aid 075558076, 10558086, and 2005/17GS0203 and by Iwatani Naoji Foundation Grant 04-3114.

REFERENCES

  • Andrews, A. E., and Coauthors, 2001: Mean ages of stratospheric air derived from in situ observations of CO2, CH4, and N2O. J. Geophys. Res., 106 , 3229532314.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Aoki, S., Nakazawa T. , Murayama S. , and Kawaguchi S. , 1992: Measurements of atmospheric methane at Japanese Antarctic Station, Syowa. Tellus, 44B , 273281.

    • Search Google Scholar
    • Export Citation
  • Aoki, S., and Coauthors, 2003: Carbon dioxide variations in the stratosphere over Japan, Scandinavia and Antarctica. Tellus, 55B , 178186.

    • Search Google Scholar
    • Export Citation
  • Bischof, W., Borchers R. , Fabian P. , and Krueger B. C. , 1985: Increased concentration and vertical distribution of carbon dioxide in the stratosphere. Nature, 316 , 708710.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Boering, K. A., and Coauthors, 1995: Measurements of stratospheric carbon dioxide and water vapor at northern midlatitudes: Implications for troposphere-to-stratosphere transport. Geophys. Res. Lett., 22 , 27372740.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Engel, A., and Coauthors, 2009: Age of stratospheric air unchanged within uncertainties over the past 30 years. Nature Geosci., 2 , 2831. doi:10.1038/ngeo388.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Honda, H., Aoki S. , Nakazawa T. , Morimoto S. , and Yajima N. , 1996a: Cryogenic air sampling system for measurements of the concentrations of stratospheric trace gases and their isotopic ratios over Antarctica. J. Geomagn. Geoelectr., 48 , 11451155.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Honda, H., and Coauthors, 1996b: A newly developed grab sampling system for collecting storatospheric air over Antarctic. Antarct. Rec., 40 , 156168.

    • Search Google Scholar
    • Export Citation
  • Ishidoya, S., Aoki S. , and Nakazawa T. , 2003: High precision measurements of the atmospheric O2/N2 ratio on a mass spectrometer. J. Meteor. Soc. Japan, 81 , 127140.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ishijima, K., Nakazawa T. , Sugawara S. , Aokli S. , and Saeki T. , 2001: Concentration variations of tropospheric nitrous oxide over Japan. Geophys. Res. Lett., 28 , 171174.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lueb, R. A., Ehhalt D. H. , and Heidt L. E. , 1975: Balloon-borne low temperature air sampler. Rev. Sci. Instrum., 46 , 702705.

  • Morimoto, S., Nakazawa T. , Aoki S. , Hashida G. , and Yamanouchi T. , 2003: Concentration variation of the atmospheric CO2 observed at Syowa Station, Antarctica from 1984 to 2000. Tellus, 55B , 170177.

    • Search Google Scholar
    • Export Citation
  • Morimoto, S., Aoki S. , Nakazawa T. , and Yamanouchi T. , 2006: Temporal variations of the carbon isotopic ratio of atmospheric methane observed at Ny Ålesund, Svalbard from 1996 to 2004. Geophys. Res. Lett., 33 , L01807. doi:10.1029/2005GL024648.

    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., Morimoto S. , Aoki S. , and Tanaka M. , 1993: Time and space variations of the carbon isotopic ratio of the tropospheric carbon dioxide over Japan. Tellus, 45B , 258274.

    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., Machida T. , Sugawara S. , Murayama S. , Morimoto S. , Hashida G. , Honda H. , and Itoh T. , 1995: Measurement of the stratospheric carbon dioxide concentration over Japan using a balloon-borne cryogenic sampler. Geophys. Res. Lett., 22 , 12291232.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., and Coauthors, 2002: Variations of stratospheric trace gases measured using a balloon-borne cryogenic sampler. Adv. Space Res., 30 , 13491357.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ng, K. C., Xue H. , and Wang J. B. , 2002: Experimental and numerical study on a miniature Joule-Thomson cooler for steady-state characteristics. Int. J. Heat Mass Transfer, 45 , 609618.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rohs, S., and Coauthors, 2006: Long-term changes of methane and hydrogen in the stratosphere in the period 1978–2003 and their impact on the abundance of stratospheric water vapor. J. Geophys. Res., 111 , D14315. doi:10.1029/2005JD006877.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schmidt, U., and Khedim A. , 1991: In situ measurements of carbon dioxide in the winter Arctic vortex and at midlatitudes: An indicator of the ‘age’ of stratospheric air. Geophys. Res. Lett., 18 , 763766.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schmidt, U., Kulessa G. , Klein E. , Röth E. P. , Fabian P. , and Borchers R. , 1987: Intercomparison of balloon-borne cryogenic whole air samplers during the MAP/GLOBUS 1983 campaign. Planet. Space Sci., 35 , 647656.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sugawara, S., Nakazawa T. , Shirakawa Y. , Kawamura K. , Aoki S. , Machida T. , and Honda H. , 1997: Vertical profile of the carbon isotopic ratio of stratospheric methane over Japan. Geophys. Res. Lett., 24 , 29892992.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tanaka, M., Nakazawa T. , and Aoki S. , 1983: High quality measurements of the concentration of atmospheric carbon dioxide. J. Meteor. Soc. Japan, 61 , 678685.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Toyoda, S., and Yoshida N. , 1999: Determination of nitrogen isotopomers of nitrous oxide on a modified isotope ratio mass spectrometer. Anal. Chem., 71 , 47114718.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Toyoda, S., and Coauthors, 2004: Temporal and latitudinal distributions of stratospheric N2O isotopomers. J. Geophys. Res., 109 , D08308. doi:10.1029/2003JD004316.

    • Search Google Scholar
    • Export Citation
  • WMO, 2008: GAW data, Volume IV—Greenhouse gases and other atmospheric gases. WMO WDCGG data summary 32, 101 pp.

Fig. 1.
Fig. 1.

Schematic of the J–T minicooler and sheath tube. Open arrows indicate directions of gas flow. Units are in millimeters.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 2.
Fig. 2.

Temperature change of the neon gas at the expansion orifice of the J–T minicooler for four different initial pressures. The neon gas is precooled by liquid nitrogen before entering the J–T minicooler.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 3.
Fig. 3.

Cross section of the J–T sampler. Flows of neon gas and sample air are shown by broken and solid lines, respectively.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 4.
Fig. 4.

Schematic of the air sampling experiment setup in the laboratory. Abbreviations in the figure are as follows: P for pressure sensor, PS for pressure switch, SV for solenoid valve, AV for pneumatic valve, MFM for mass flowmeter, and F for inline filter.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 5.
Fig. 5.

Time series of the neon gas pressure and air sampling rate when the pressure of the air sample in the chamber is set to 60 hPa. The neon gas is supplied from a 2-L cylinder at 19.0 MPa.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 6.
Fig. 6.

Relationship between the sample pressure in the chamber and the amount of air sample collected by the J–T sampler. Solid and open circles represent the results when the pressure of liquid nitrogen is the same as ambient pressure and 0.1 MPa higher than the ambient, respectively. Closed triangles are the sample amount collected at altitudes of 18 and 25 km over Syowa Station.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 7.
Fig. 7.

Schematic of the compact cryogenic sampler for balloon experiments. Units are in millimeters.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 8.
Fig. 8.

Trajectories of the compact cryogenic samplers launched from Syowa Station on 4 Jan 2008.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Fig. 9.
Fig. 9.

(a) CH4 and (b) N2O concentrations observed in the stratosphere over Syowa Station in January 1998 (open squares with cross), January 2004 (open circles), and January 2008 (solid triangles). (c) Relationship between the CH4 and N2O concentrations shown in (a), (b). Fitted linear line is based on the 1998 and 2004 data.

Citation: Journal of Atmospheric and Oceanic Technology 26, 10; 10.1175/2009JTECHA1283.1

Table 1.

Summary description of the balloon experiments at Syowa Station. Total weight includes the weight of the plastic balloon, which was launched 4 Jan 2008.

Table 1.
Save
  • Andrews, A. E., and Coauthors, 2001: Mean ages of stratospheric air derived from in situ observations of CO2, CH4, and N2O. J. Geophys. Res., 106 , 3229532314.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Aoki, S., Nakazawa T. , Murayama S. , and Kawaguchi S. , 1992: Measurements of atmospheric methane at Japanese Antarctic Station, Syowa. Tellus, 44B , 273281.

    • Search Google Scholar
    • Export Citation
  • Aoki, S., and Coauthors, 2003: Carbon dioxide variations in the stratosphere over Japan, Scandinavia and Antarctica. Tellus, 55B , 178186.

    • Search Google Scholar
    • Export Citation
  • Bischof, W., Borchers R. , Fabian P. , and Krueger B. C. , 1985: Increased concentration and vertical distribution of carbon dioxide in the stratosphere. Nature, 316 , 708710.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Boering, K. A., and Coauthors, 1995: Measurements of stratospheric carbon dioxide and water vapor at northern midlatitudes: Implications for troposphere-to-stratosphere transport. Geophys. Res. Lett., 22 , 27372740.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Engel, A., and Coauthors, 2009: Age of stratospheric air unchanged within uncertainties over the past 30 years. Nature Geosci., 2 , 2831. doi:10.1038/ngeo388.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Honda, H., Aoki S. , Nakazawa T. , Morimoto S. , and Yajima N. , 1996a: Cryogenic air sampling system for measurements of the concentrations of stratospheric trace gases and their isotopic ratios over Antarctica. J. Geomagn. Geoelectr., 48 , 11451155.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Honda, H., and Coauthors, 1996b: A newly developed grab sampling system for collecting storatospheric air over Antarctic. Antarct. Rec., 40 , 156168.

    • Search Google Scholar
    • Export Citation
  • Ishidoya, S., Aoki S. , and Nakazawa T. , 2003: High precision measurements of the atmospheric O2/N2 ratio on a mass spectrometer. J. Meteor. Soc. Japan, 81 , 127140.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ishijima, K., Nakazawa T. , Sugawara S. , Aokli S. , and Saeki T. , 2001: Concentration variations of tropospheric nitrous oxide over Japan. Geophys. Res. Lett., 28 , 171174.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lueb, R. A., Ehhalt D. H. , and Heidt L. E. , 1975: Balloon-borne low temperature air sampler. Rev. Sci. Instrum., 46 , 702705.

  • Morimoto, S., Nakazawa T. , Aoki S. , Hashida G. , and Yamanouchi T. , 2003: Concentration variation of the atmospheric CO2 observed at Syowa Station, Antarctica from 1984 to 2000. Tellus, 55B , 170177.

    • Search Google Scholar
    • Export Citation
  • Morimoto, S., Aoki S. , Nakazawa T. , and Yamanouchi T. , 2006: Temporal variations of the carbon isotopic ratio of atmospheric methane observed at Ny Ålesund, Svalbard from 1996 to 2004. Geophys. Res. Lett., 33 , L01807. doi:10.1029/2005GL024648.

    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., Morimoto S. , Aoki S. , and Tanaka M. , 1993: Time and space variations of the carbon isotopic ratio of the tropospheric carbon dioxide over Japan. Tellus, 45B , 258274.

    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., Machida T. , Sugawara S. , Murayama S. , Morimoto S. , Hashida G. , Honda H. , and Itoh T. , 1995: Measurement of the stratospheric carbon dioxide concentration over Japan using a balloon-borne cryogenic sampler. Geophys. Res. Lett., 22 , 12291232.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nakazawa, T., and Coauthors, 2002: Variations of stratospheric trace gases measured using a balloon-borne cryogenic sampler. Adv. Space Res., 30 , 13491357.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ng, K. C., Xue H. , and Wang J. B. , 2002: Experimental and numerical study on a miniature Joule-Thomson cooler for steady-state characteristics. Int. J. Heat Mass Transfer, 45 , 609618.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rohs, S., and Coauthors, 2006: Long-term changes of methane and hydrogen in the stratosphere in the period 1978–2003 and their impact on the abundance of stratospheric water vapor. J. Geophys. Res., 111 , D14315. doi:10.1029/2005JD006877.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schmidt, U., and Khedim A. , 1991: In situ measurements of carbon dioxide in the winter Arctic vortex and at midlatitudes: An indicator of the ‘age’ of stratospheric air. Geophys. Res. Lett., 18 , 763766.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schmidt, U., Kulessa G. , Klein E. , Röth E. P. , Fabian P. , and Borchers R. , 1987: Intercomparison of balloon-borne cryogenic whole air samplers during the MAP/GLOBUS 1983 campaign. Planet. Space Sci., 35 , 647656.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sugawara, S., Nakazawa T. , Shirakawa Y. , Kawamura K. , Aoki S. , Machida T. , and Honda H. , 1997: Vertical profile of the carbon isotopic ratio of stratospheric methane over Japan. Geophys. Res. Lett., 24 , 29892992.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tanaka, M., Nakazawa T. , and Aoki S. , 1983: High quality measurements of the concentration of atmospheric carbon dioxide. J. Meteor. Soc. Japan, 61 , 678685.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Toyoda, S., and Yoshida N. , 1999: Determination of nitrogen isotopomers of nitrous oxide on a modified isotope ratio mass spectrometer. Anal. Chem., 71 , 47114718.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Toyoda, S., and Coauthors, 2004: Temporal and latitudinal distributions of stratospheric N2O isotopomers. J. Geophys. Res., 109 , D08308. doi:10.1029/2003JD004316.

    • Search Google Scholar
    • Export Citation
  • WMO, 2008: GAW data, Volume IV—Greenhouse gases and other atmospheric gases. WMO WDCGG data summary 32, 101 pp.

  • Fig. 1.

    Schematic of the J–T minicooler and sheath tube. Open arrows indicate directions of gas flow. Units are in millimeters.

  • Fig. 2.

    Temperature change of the neon gas at the expansion orifice of the J–T minicooler for four different initial pressures. The neon gas is precooled by liquid nitrogen before entering the J–T minicooler.

  • Fig. 3.

    Cross section of the J–T sampler. Flows of neon gas and sample air are shown by broken and solid lines, respectively.

  • Fig. 4.

    Schematic of the air sampling experiment setup in the laboratory. Abbreviations in the figure are as follows: P for pressure sensor, PS for pressure switch, SV for solenoid valve, AV for pneumatic valve, MFM for mass flowmeter, and F for inline filter.

  • Fig. 5.

    Time series of the neon gas pressure and air sampling rate when the pressure of the air sample in the chamber is set to 60 hPa. The neon gas is supplied from a 2-L cylinder at 19.0 MPa.

  • Fig. 6.

    Relationship between the sample pressure in the chamber and the amount of air sample collected by the J–T sampler. Solid and open circles represent the results when the pressure of liquid nitrogen is the same as ambient pressure and 0.1 MPa higher than the ambient, respectively. Closed triangles are the sample amount collected at altitudes of 18 and 25 km over Syowa Station.

  • Fig. 7.

    Schematic of the compact cryogenic sampler for balloon experiments. Units are in millimeters.

  • Fig. 8.

    Trajectories of the compact cryogenic samplers launched from Syowa Station on 4 Jan 2008.

  • Fig. 9.

    (a) CH4 and (b) N2O concentrations observed in the stratosphere over Syowa Station in January 1998 (open squares with cross), January 2004 (open circles), and January 2008 (solid triangles). (c) Relationship between the CH4 and N2O concentrations shown in (a), (b). Fitted linear line is based on the 1998 and 2004 data.

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