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The regional budget of methane (CH4) emissions for East Asia, a crucial region in the global greenhouse gas budget, was quantified for 1990–2015 with a bottom-up method based on inventories and emission model simulations. Anthropogenic emissions associated with fossil fuel extraction, industrial activities, waste management, and agricultural activities were derived from the Emission Database for Global Atmospheric Research version 4.3.2 and compared with other inventories. Emissions from natural wetlands and CH4 uptake by upland soil oxidation were estimated using the Vegetation Integrative SImulator for Trace gases (VISIT), a biogeochemical model that considers historical land use and climatic conditions. Emissions from biomass burning and termites were calculated using satellite and land-use data combined with empirical emission factors. The resulting average annual estimated CH4 budget for 2000–2012 indicated that East Asia was a net source of 67.3 Tg CH4 yr−1, of which 88.8% was associated with anthropogenic emissions. The uncertainty (±standard deviation) of this estimate, ±14 Tg CH4 yr−1, stemmed from data and model inconsistencies. The increase of the net flux from 60.2 Tg CH4 yr−1 in 1990 to 78.0 Tg CH4 yr−1 in 2012 was due mainly to increased emissions by the fossil fuel extraction and livestock sectors. Our results showed that CH4 was a crucial component of the regional greenhouse gas budget. A spatial analysis using 0.25° × 0.25° grid cells revealed emission hotspots in urban areas, agricultural areas, and wetlands. These hotspots were surrounded by weak sinks in upland areas. The estimated natural and anthropogenic emissions fell within the range of independent estimates, including top-down estimates from atmospheric inversion models. Such a regional accounting is an effective way to elucidate climatic forcings and to develop mitigation policies. Further studies, however, are required to reduce the uncertainties in the budget.

Atmospheric CH4 mole fractions were observed aboard the R/V Mirai sailing in waters off Alaska in the Arctic Ocean in September 2012–2017 to investigate the CH4 emissions from the surrounding region, especially from the East Siberian Arctic Shelf (ESAS). The synoptic-scale increases of CH4 were compared with simulated increases based on a Lagrangian Particle Dispersion Model and monthly CH4 flux maps determined by a global atmospheric inversion system. There were good agreements between the observed and simulated CH4 increases, suggesting the validity of CH4 fluxes from the surrounding areas of the cruise experiments. The CH4 emissions from the ESAS in September were further optimized in order to minimize the root mean square of the differences between the observed and simulated CH4 increases. The average (±1σ) of the resulting emission rates was 0.58 ± 0.47 TgCH4 yr−1, which was much smaller than previously reported estimates. The individual optimized CH4 emissions varied from −0.1 ± 0.3 to 1.3 ± 0.4 TgCH4 yr−1, showing a positive correlation with the sea surface temperature and a negative correlation with the ice concentration of the ESAS area in September. These results suggest a possible enhancement of the CH4 emissions from the ESAS in a warmer future.

Initial conditions of trajectory calculation in studies of atmospheric transport are often arbitrary, leading to questions on applying trajectories to atmospheric observations of green house gases. We used observed methane on Hateruma Island in 1996–2000 as a tracer to investigate the quality of variety length of trajectories obtained from a three-dimensional (3D) and an isentropic (IS) model with different starting altitudes. The trajectory altitude is also considered in trajectory quality analysis. Our approach is to analyze the correlation between methane variation and the displacement of trajectory pairs. The study shows that the 3D model gives more accurate trajectories than the IS model, especially when long trajectories with high-altitude endpoints are to be used; and that a low starting altitude should be used for trajectory calculation by the IS model; however, for the 3D model a starting altitude close to the surface may affect trajectory quality due to the effect of zero vertical wind on the surface. The appropriate trajectory length for Hateruma Island is 78 h when the 3D model is used and 54 h when the IS model is used.

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.

An infrared absorption spectroscopy remote sensing technique was used to determine the SO 2 /HCl ratio in fumarolic plumes at Vulcano, Italy. The measurements were made from the southern crater rim of Fossa Grande Crater, about 400 m from the fumarolic area in the crater. Infrared absorption spectra of HCl and SO 2 were observed for four fumaroles a few tens of metres apart using the hot fumarolic surface as an infrared light source. The measured SO 2 /HCl ratios in the FA, F47, FW and lower parti of the F21 fumaroles were 4.5–5.4, 3.5, 9.5–11.2 and 5.8 respectively. The SO 2 /HCl ratio of the FA fumarole was higher than that of the gas collected directly in the fumarolic vent (SO 2 /HCl ratio = 2.9), and was closer to the S (total) /HCl ratio (= 4.6) of the collected gas. Our results show that the SO 2 /HCl ratios of two fumaroles only a few tens of metres apart exhibits differences of about twofold. This suggests that this remote monitoring technique is capable of detecting spatial distribution in the SO 2 /HCl ratios of volcanic plumes. Because temporal variations in S/Cl ratios can provide precursory signals for volcanic eruptions [1–3], this remote sensing technique can used efficiently for evaluation of volcanic activity.

For the purpose of investigating the areal distribution of atmospheric methane, we have constructed a continuous measurement system using a flame ionization detector (FID). Since the FID has high sensitivity to almost all hydrocarbons, non-methane hydrocarbons in sample air were reduced by being passed through a heated column filled with Pt catalyst. Through this treatment, non-methane hydrocarbons were effectively reduced, and a low detection limit of 0.004 ppmv and short response time of about 10 s were attained. By using this system mounted on a vehicle, the areal distribution of atmospheric methane was measured in two typical source areas: rice paddies and a natural gas field. In the case of the gas field, we estimated the emission rate of methane based on the observed profile of methane plumes.