Abstract. We examined potential interferences from water vapor and atmospheric background gases (N 2 , O 2 , and Ar), and biases by isotopologues of target species, on accurate measurement of atmospheric CO 2 and CH 4 by means of wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). Changes of the background gas mole fractions in the sample air substantially impacted the CO 2 and CH 4 measurements: variation of CO 2 and CH 4 due to relative increase of each background gas increased as Ar < O 2 < N 2 , suggesting similar relation for the pressure-broadening effects (PBEs) among the background gas. The pressure-broadening coefficients due to variations in O 2 and Ar for CO 2 and CH 4 are empirically determined from these experimental results. Calculated PBEs using the pressure-broadening coefficients are linearly correlated with the differences between the mole fractions of O 2 and Ar and their ambient abundances. Although the PBEs calculation showed that impact of natural variation of O 2 is negligible on the CO 2 and CH 4 measurements, significant bias was inferred for the measurement of synthetic standard gases. For gas standards balanced with purified air, the PBEs were estimated to be marginal (up to 0.05 ppm for CO 2 and 0.01 ppb for CH 4 ) although the PBEs were substantial (up to 0.87 ppm for CO 2 and 1.4 ppb for CH 4 ) for standards balanced with synthetic air. For isotopic biases on CO 2 measurements, we compared experimental results and theoretical calculations, which showed excellent agreement within their uncertainty. We derived instrument-specific water correction functions empirically for three WS-CRDS instruments (Picarro EnviroSense 3000i, G-1301, and G-2301), and evaluated the transferability of the water correction function from G-1301 among these instruments. Although the transferability was not proven, no significant difference was found in the water vapor correction function for the investigated WS-CRDS instruments as well as the instruments reported in the past studies within the typical analytical precision at sufficiently low water concentrations (< 0.7 % for CO 2 and < 0.6 % for CH 4 ). For accurate measurements of CO 2 and CH 4 in ambient air, we concluded that WS-CRDS measurements should be performed under complete dehumidification of air samples, or moderate dehumidification followed by application of a water vapor correction function, along with calibration by natural airbased standard gases or purified air-balanced synthetic standard gases with the isotopic correction.

Abstract. In situ observation of the atmospheric CO2, CH4, and CO mixing ratios at Hateruma Island (HAT, 24.05° N, 123.80° E) often show synoptic-scale variations with correlative elevations during winter, associated with air transport from the East Asian countries. We examine winter (November– March) trends in ΔCH4 / ΔCO2, ΔCO / ΔCO2, and ΔCO / ΔCH4 observed at Hateruma over the period 1999 to 2010. To investigate the relationship between the East Asian emissions and the short-term variations in the atmospheric mixing ratios, we use the FLEXPART Lagrangian particle dispersion model (LPDM). The observed ratios ΔCH4 / ΔCO2 and ΔCO / ΔCO2 both show an overall gradual decrease over the study period due to a recent rapid increase in fossil fuel consumption in China. We note, however, that the decreasing rates of ΔCH4 / ΔCO2 and ΔCO / ΔCO2 show gradual decrease and increase, respectively, during the entire observation periods used in this study. The ΔCO / ΔCH4 slope, on the other hand, shows an increasing trend during 1999–2004 but a decrease during 2005–2010. Calculation of the concentration footprint for the atmospheric observation at HAT by using the FLEXPART LPDM indicates that most of the short-term variations are caused by emission variations from northern and eastern China. Combined with a set of reported emission maps, we have estimated the temporal changes in the annual CH4 and CO emissions from China under the assumption that the estimate of the fossil-fuel-derived CO2 emissions based on the energy statistics are accurate. The estimated annual CH4 emissions, corresponding to nonseasonal sources or anthropogenic sources without rice fields, show a nearly constant value of 39 ± 7 TgCH4 yr−1 during 1998–2002, and then gradually increase to 46 ± 8 TgCH4 yr−1 in 2009/2010. The estimated annual CO emissions increase from 134 ± 32 TgCO yr−1 in 1998/1999 to 182 ± 42 TgCO yr−1 in 2004/2005, level off after 2005, and then slightly decrease to less than 160 TgCO yr−1 in 2008–2010.

[1] Nondispersive infrared (NDIR) CO 2 analyzer could produce erroneous CO 2 mole fraction measurements for an air sample when CO 2 -in-air mixtures having different isotopic compositions than atmospheric CO 2 are used as the NDIR calibration gases. This is because (1) an optical band-pass filter equipped in a typical NDIR analyzer to minimize the interference effect from the other infrared-active species is basically designed to transmit only the absorption band of 12 C 16 O 2 and (2) absorption bands for the other CO 2 -related isotopologues, for example, 13 C 16 O 2 , are shifted to lower wave numbers depending on their isotope effects. To evaluate the effect of the isotopic composition on the NDIR response, we computed the theoretical relative molar response of the instrument to each isotopologue based on the infrared absorptance by the individual isotopologues. We then prepared a gravimetric 13 CO 2 -in-air mixture with CO 2 mole fraction of 380 ppm to experimentally determine the optical filter property. The apparent mole fractions of the 13 CO 2 -in-air mixture determined by three NDIR analyzers used in this study were 46, 94, and 27 ppm, indicating that the optical filters in these instruments substantially reduced the response to

The reaction of laser-evaporated iron atoms with methane gas was studied using a matrix-isolation technique, and the reaction products were observed by Mössbauer and infrared spectroscopy. The reaction produced CH3FeH in a CH4/Ar mixture, whereas Fe2H2(CH3)4 was also obtained in addition in a pure CH4 matrix. Molecular orbital calculations were performed in order to confirm the assignments.

No abstract