Yasunori Tohjima

Permeation of atmospheric gases through polymer O-rings used in flasks for air sampling

[1] Permeation of various gases through elastomeric O-ring seals can have important effects on the integrity of atmospheric air samples collected in flasks and measured some time later. Depending on the materials and geometry of flasks and valves and on partial pressure differences between sample and surrounding air, the concentrations of different components of air can be significantly altered during storage. The influence of permeation is discussed for O-2/N-2, Ar/N-2, CO2, delta(13) C in CO2, and water vapor. Results of sample storage tests for various flask and valve types and different storage conditions are presented and are compared with theoretical calculations. Effects of permeation can be reduced by maintaining short storage times and small partial pressure differences and by using a new valve design that buffers exchange of gases with surrounding air or by using less permeable materials ( such as Kel-F) as sealing material. General awareness of possible permeation effects helps to achieve more reliable measurements of atmospheric composition with flask sampling techniques.

Method for measuring changes in the atmospheric O2/N2 ratio by a gas chromatograph equipped with a thermal conductivity detector

We present a method for measuring changes in the atmospheric O2/N2 ratio based on data from a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD). In this method, O2 and N2 in an air sample are separated on a column filled with molecular sieve 5A with H2 carrier gas. Since the separated O2 includes Ar, which has a retention time similar to that of O2, the (O2+Ar)/N2 ratio is actually measured. The change in the measured (O2+Ar)/N2 ratio can be easily converted to that in the O2/N2 ratio with a very small error based on the fact that the atmospheric Ar/N2 ratio is almost constant. The improvements to achieve the high-precision measurement include stabilization of the pressure at the GC column head and at the outlets of the TCD and the sample loop. Additionally, the precision is improved statistically by repeating alternate analyses of sample and a reference gas. The standard deviation of the replicate cycles of reference and sample analyses is about 18 per meg (corresponding to 3.8 parts per million (ppm) O2 in air). This means that the standard error is about 7 per meg (1.5 ppm O2 in air) for seven cycles of alternate analyses, which takes about 70 min. The response of this method is likely to have a 2% nonlinearity. Ambient air samples are collected under pressure in glass flasks equipped with two stopcocks sealed by Viton O-rings at both ends. Pressure depletion in the flask during the O2/N2 measurement does not cause any detectable change in the O2/N2 ratio, but the O2/N2 ratio in the flask was found to gradually decrease during the storage period. We also present preliminary results from air samples collected at Hateruma Island (latitude 24°03′N, longitude 123°49′) from July 1997 through March 1999. The observed O2/N2 ratios clearly show a seasonal variation, increasing in spring and summer and decreasing in autumn and winter.

Atmospheric O2/N2 measurements at two Japanese sites: estimation of global oceanic and land biotic carbon sinks and analysis of the variations in atmospheric potential oxygen (APO)

We present measurements of atmospheriCO2/N2 and CO2 mixing ratios taken at Hateruma Island (HAT) and Cape Ochi-Ishi (COI) in Japan. Global carbon sinks are estimated from the tracer atmospheric potential oxygen (APO) calculated as the weighted sums of the observed O2/N2 and CO2, and the global CO2 data from the NOAA/ESRL GMD flask sampling network. The oceanic and land biotic sinks are 2.4 ± 0.7 and 0.5 ± 0.9 Pg C yr-1, respectively, for the 7-yr period (July 1998–July 2005) and 2.1 ± 0.7 and 1.0 ± 0.9 Pg C yr-1, respectively, for the 6-yr period (July 1999–July 2005). The former 7-yr estimates are based on the data from HAT only, while the latter 6-yr estimates are obtained using data from both HAT and COI. These estimations include an ocean outgassing correction of 0.48 Pg C yr-1. The instantaneous rates of change in the APO trends show large interannual variability with peak-to-peak amplitudes of about 30 per meg yr-1. The winter anomalies in the APO trend are the major contributor to the interannual variability, and the oceanic O2 influx associated with winter ventilation may be a significant cause of the variability in APO

Distribution of tropospheric methane over Siberia in July 1993

Airborne observations of atmospheric methane (CH4) mixing ratid were carried out over Siberia during July 15-30, 1993, using a continuous measurement system. The distribution of CH 4 in the upper troposphere at an altitude of about 7 km was highly variable (1.72-1.91 parts per million, or ppm), being affected by intrusion of stratospheric air, long-range transport of CH 4 from the source region, and a synoptic-scale mixing process. During flights along nearly constant latitude between Yakutsk (62.10°N, 129.50°E) and Nizhnevartovsk (60.57°N, 76.40°E) on July 19 and 28 we observed large-scale enhancements of CH 4 from near 90° to 100°E with a horizontal scale of more than 500 km. Accompanied by high humidity and low mixing ratios of CO 2 and O 3 , the air masses with enhanced CH 4 mixing ratio were considered to be affected by lower tropospheric air. The probable source region of the CH 4 was inferred to be the West Siberian Lowland, which contains vast wetlands and huge oil/gas fields. The distribution of CH 4 in the lower troposphere (0.1-3 km) over the boreal wetlands in the West Siberian Lowland, ranging from 1.85 ppm to 2.75 ppm, showed large accumulations near the ground in the morning. The short-term temporal variations in the vertical profile of CH 4 mixing ratio revealed that the accumulated CH 4 was transported to the free troposphere with the growth of the mixed layer. On the other hand, the distribution of CH 4 (0.1-1 km) over the tundra areas in the Siberian Arctic was less variable (1.81-1.84 ppm), and little accumulation was observed.

Methane emissions in East Asia for 2000–2011 estimated using an atmospheric Bayesian inversion

We present methane (CH4) emissions for East Asia from a Bayesian inversion of CH4 mole fraction and stable isotope (δ13C-CH4) measurements. Emissions were estimated at monthly resolution from 2000 to 2011. A posteriori, the total emission for East Asia increased from 43 ± 4 to 59 ± 4 Tg yr−1 between 2000 and 2011, owing largely to the increase in emissions from China, from 39 ± 4 to 54 ± 4 Tg yr−1, while emissions in other East Asian countries remained relatively stable. For China, South Korea, and Japan, the total emissions were smaller than the prior estimates (i.e., Emission Database for Global Atmospheric Research 4.2 FT2010 for anthropogenic emissions) by an average of 29%, 20%, and 23%, respectively. For Mongolia, Taiwan, and North Korea, the total emission was less than 2 Tg yr−1 and was not significantly different from the prior. The largest reductions in emissions, compared to the prior, occurred in summer in regions important for rice agriculture suggesting that this source is overestimated in the prior. Furthermore, an analysis of the isotope data suggests that the prior underestimates emissions from landfills and ruminant animals for winter 2010 to spring 2011 (no data available for other times). The inversion also found a lower average emission trend for China, 1.2 Tg yr−1 compared to 2.8 Tg yr−1 in the prior. This trend was not constant, however, and increased significantly after 2005, up to 2.0 Tg yr−1. Overall, the changes in emissions from China explain up to 40% of the increase in global emissions in the 2000s.

Variations in atmospheric nitrous oxide observed at Hateruma monitoring station

Abstract In situ measurement of atmospheric nitrous oxide (N 2 O) has been carried out at Hateruma monitoring station (lat 24°03 ′ N, long 123°48 ′ E) since March 1996 by the National Institute for Environmental Studies (NIES). A fully automated gas chromatograph equipped with an electron capture detector (ECD) measures the N 2 O concentrations at a frequency of 3 air samples per hour. Details of the experimental methods and procedures are presented in this paper. The N 2 O concentrations observed from March 1996 to February 1999 increased at an average rate of 0.64 ppb/yr. The observed data also suggest that there is a weak annual cycle of N 2 O concentration, increasing in autumn and winter and decreasing in spring and summer, with a peak-to-peak amplitude of at most 0.3 ppb. The N 2 O mixing ratios, smoothed with the 24-h running average, clearly showed short-term variability with synoptic timescales and had peak-to-peak amplitudes of about 1 ppb or less. These short-term variations correlated positively with the short-term variations of CO 2 during the period from winter to early spring when the air masses arriving at Hateruma are dominantly transported from the Asian continent. The ΔN 2 O/ΔCO 2 ratios could be used to constrain the relative strengths of these fluxes on a regional scale.

ENSO-related variability in latitudinal distribution of annual mean atmospheric potential oxygen (APO) in the equatorial Western Pacific

We examined temporal variations in the latitudinal distribution of annual mean atmospheric potential oxygen (APO=O2+1.1×CO2), a useful tracer for studying ocean biogeochemical processes. To compute APO, we used atmospheric CO2 and O2 concentrations from flask samples and in-situ measurements onboard commercial cargo ships sailing between Japan and Australia/New Zealand. Most of the observed latitudinal distributions of the annual mean APO for the years 2002–2012 showed equatorial bulges, indicating tropical APO outgassing fluxes. However, the equatorial bulge was noticeably absent during the 2009/2010 El Niño period, especially in the Southern Hemisphere. The temporal variation in the 25–0°S latitudinal APO gradient correlated significantly with the El Niño/Southern Oscillation (ENSO); the equatorward APO gradients decreased (increased) during the El Niño (La Niña) period with a variability of about ±0.1 per meg/degree. Simulated APO based on an atmospheric transport model driven by climatological/constant flux fields and reanalysis meteorological data reproduced the overall characteristic of the observed temporal variation in the APO gradients well, suggesting that the atmospheric transport contributed substantially to the observed interannual variation in the global APO distributions. However, the model simulation underestimated the variability in the APO gradients by about 25%, compared to the observations. These discrepancies suggest a possibility of the existence of additional APO flux variability in the tropical Pacific, enhancing the ENSO-related variability in the observed APO gradients.

CO emissions from biomass burning in South-east Asia in the 2006 El Nino year: shipboard and AIRS satellite observations

Environmental context Atmospheric carbon monoxide greatly affects the abundance of environmentally important gases, including methane, hydrochlorofluorocarbons and tropospheric ozone. We present evidence for episodes of CO pollution over the tropical Pacific Ocean resulting from intensive biomass burning in South-east Asia and Northern Australia during the 2006 El Nino year. We discuss the locations of the CO emissions and their long-range transport. Abstract Biomass burning is often associated with climate oscillations. For example, biomass burning in South-east Asia is strongly linked to El Nino–southern oscillation activity. During October and November of the 2006 El Nino year, a substantial increase in CO mixing ratios was detected over the Western tropical Pacific Ocean by shipboard observations routinely operated between Japan and Australia and New Zealand. Combining in-situ measurements, satellite observations, and an air trajectory model simulation, two high CO episodes were identified originating from biomass burning in Borneo, Sumatra, New Guinea, and Northern Australia. Between 15°N and the Equator, marked CO enhancements were encountered associated with a significant correlation between CO and CO2 and between CO and O3. The ΔCO/ΔCO2 ratio observed in the fire plume was considerably high (171 ppbv ppmv–1), suggesting substantial contributions from peat soil burning in Indonesia. In contrast, the ΔO3/ΔCO ratio was only 0.05 ppbv ppbv–1, indicating that net photochemical production of O3 in the plume was negligible during long-range transport in the lower troposphere over the Western tropical North Pacific.

Continuous Observation of Atmospheric 222Rn Concentrations for Analytic Basis of Atmospheric Transport in East Asia

The observation network of atmospheric radon-222 (222Rn) concentration established in East Asia region is introduced, and the characteristics of the observations at two continental sites Beijing and Seoul and three remote sites Cape Ochiishi, Hachijo Is. and Hateruma Is. are discussed in this paper. Higher levels of 222Rn concentrations with typical diurnal variation with early morning maxima were observed on the continent, and lower levels with no diurnal variation at remote islands. Seasonal variations with summer minima and winter maxima were commonly obtained at all five observatories, and they suggested contribution of 222Rn originated from the continent to atmospheric 222Rn over the remote islands isolated in the ocean. A backward trajectory analysis showed clear relationship between variation in wind field and in 222Rn concentration at Hachijo Is., and proved availability of the observation for analysis of atmospheric transport in East Asia.

Emissions of methane from offshore oil and gas platforms in Southeast Asia

Methane is a substantial contributor to climate change. It also contributes to maintaining the background levels of tropospheric ozone. Among a variety of CH4 sources, current estimates suggest that CH4 emissions from oil and gas processes account for approximately 20% of worldwide anthropogenic emissions. Here, we report on observational evidence of CH4 emissions from offshore oil and gas platforms in Southeast Asia, detected by a highly time-resolved spectroscopic monitoring technique deployed onboard cargo ships of opportunity. We often encountered CH4 plumes originating from operational flaring/venting and fugitive emissions off the coast of the Malay Peninsula and Borneo. Using night-light imagery from satellites, we discovered more offshore platforms in this region than are accounted for in the emission inventory. Our results demonstrate that current knowledge regarding CH4 emissions from offshore platforms in Southeast Asia has considerable uncertainty and therefore, emission inventories used for modeling and assessment need to be re-examined.