https://repository.kopri.re.kr/handle/201206/5431 2026-04-10T22:44:22Z 2026-04-10T22:44:22Z C.A.M. Brenninkmeijer Rhee, Tae Siek T. Roeckmann https://repository.kopri.re.kr/handle/201206/6605 2022-03-24T07:14:41Z 2008-01-01T00:00:00Z

Title: Hydrogen isotope fractionation in the photolysis of formaldehyde Authors: C.A.M. Brenninkmeijer; Rhee, Tae Siek; T. Roeckmann Abstract: Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in the H2 produced is 500(±20) ‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotope ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O + h？→ CHO + H) as compared to the molecular channel (CH2O + h？→ H2 + CO) of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±90) ‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotope ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2 (？m) but also by overall fractionation for the removal processes of CH2O (？f), and is represented by the ratio of ？m/？f. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of ？m/？f varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of ？m/？f can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH4) by the factor of 1.2 ？1.3 as anticipated in the literature.

2008-01-01T00:00:00Z T. Roeckmann C.A.M. Brenninkmeijer P. Fraser P. Steele Rhee, Tae Siek R. Langenfields M. Brass https://repository.kopri.re.kr/handle/201206/7764 2022-03-24T07:12:41Z 2007-01-01T00:00:00Z

Title: Seasonal and Interannual Variations of Atmospheric H2 in the Troposphere a Link of Climate Change Authors: T. Roeckmann; C.A.M. Brenninkmeijer; P. Fraser; P. Steele; Rhee, Tae Siek; R. Langenfields; M. Brass Abstract: Molecular hydrogen (H2) is the second most abundant reduced gas in the atmosphere. Like the most abundant reduced gas, CH4, atmospheric H2 is attacked by atmospheric oxidizing agent, hydroxyl radical, at a similar frequency. However, its lifetime (~1.4 years) is much shorter than CH4 (~10 years) due to its overwhelming destruction by soils. Major sources are photochemical oxidation of hydrocarbons (~50%) and combustion processes. Hydrogen economy in future may change the current atmospheric H2 cycle associated with the unavoidable leakage of H2 in the infra-structure. To assess the impact of the hydrogen economy to atmospheric environment in future, it is necessary to evaluate the present atmospheric H2 cycle as accurately as possible. Here we present atmospheric hydrogen cycles in the troposphere. Recent developments in continuous flow isotope ratio mass spectrometry allow us to obtain sufficiently precise data even using small volumes of air (0.4 L). Free tropospheric air samples have been collected with the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) Boeing 767 over Europe and Africa during 3 flights in May, July, and December to investigate temporal, spatial variations of H2 abundance. The D/H ratio as well as the H2 mixing ratio shows a clear seasonality in both hemispheres. The seasonal variation of H2 is similar to that observed in the remote marine boundary layer. However, the D/H ratio varies out of phase with the H2 concentration in the northern hemisphere, while varying in phase in the southern hemisphere. This suggests that the source or sink processes regulating the H2 mixing ratios are different in each hemisphere. We also investigate the southern hemispheric H2 cycle using D/H stable isotope analyses of H2 and CH4in 29 samples of air collected from 1992 and 2004 at the Australian Cape Grim baseline air monitoring station and stored in the unique air archive in Aspendale. A harmonic-polynomi

2007-01-01T00:00:00Z Rhee, Tae Siek P. Steele C.A.M. Brenninkmeijer P. Fraser R. Langenfields T. Roeckmann M. Brass https://repository.kopri.re.kr/handle/201206/7766 2022-03-24T07:13:47Z 2007-01-01T00:00:00Z

Title: Analysis of the southern hemispheric H2 Cycle using D/H measurements of H2 and CH4 in Cape Grim air archive Authors: Rhee, Tae Siek; P. Steele; C.A.M. Brenninkmeijer; P. Fraser; R. Langenfields; T. Roeckmann; M. Brass Abstract: Understanding the hydrogen cycle has gained additional importance because of the acknowledgement of the potential role of hydrogen as a major energy carrier in the future. We investigate the southern hemispheric H2 cycle using D/H stable isotope analyses of H2 and CH4 in 29 samples of air collected from 1992 and 2004 at the Australian Cape Grim baseline air monitoring station and stored in the unique air archive in Aspendale. The D/H ratios were determined using the fairly new technique of continuous-flow isotope ratio mass spectrometry. Quality control tests for the mixing ratios and isotope ratios of H2 in archived air confirm the absence of artifacts that could occur during the collection and subsequent storage. A harmonic-polynomial function was applied to isolate seasonal variation and long term trends during the period of observation. Mean seasonal variations of the D/H ratio of H2 reveal a similar in-phase variation as observed in the southern hemispheric free troposphere (CARIBIC flights). The long-term trends for the mixing ratios and the D/H ratios of H2 and CH4 show a remarkable feature of the SH H2 cycle, namely, the rate of increase of CH4 is about 3.8 times faster than that of H2, whereas the D/H ratio of CH4 increases about 1.8 times slower than that for H2. This paradox cannot be explained by the photochemical oxidation of CH4 and H2 in the southern hemisphere as the major process for these long-term trends. We suspect a strong external influences acting like source or sink for H2 in the form of inter-hemispheric exchange of air masses.

2007-01-01T00:00:00Z Rhee, Tae Siek T. Roeckmann C.A.M. Brenninkmeijer https://repository.kopri.re.kr/handle/201206/7763 2022-03-24T07:13:47Z 2007-01-01T00:00:00Z

Title: Hydrogen Isotope Fractionation during the destruction of formaldehyde in the atmosphere Authors: Rhee, Tae Siek; T. Roeckmann; C.A.M. Brenninkmeijer Abstract: Due to the limited fossil energy sources and the climate impact of their final products CO2, hydrogen economy has been considered to be alternative. Large scale use of H2 as an energy carrier may perturb the current global H2 cycle. Molecular hydrogen in the atmosphere originates from direct emissions from the Earth surfaces and from airborne production by photolysis of formaldehyde. It is destroyed by the reactions with the OH radical in the atmosphere and with microbes in soils. Measurement of stable isotope ratio of H2 turns out to be useful to investigate atmospheric H2 cycle. Among the sources, photochemically produced H2 is uniquely enriched in deuterium compared to the isotopic ratio of atmospheric H2. Here we investigated isotopic fractionation of hydrogen species produced from photochemical reactions of CH2O. Experiments were conducted to determine the isotopic fractionation of the H2 produced by photolysis of CH2O in flask under atmospheric conditions. The H2 produced is depleted in deuterium by 500 ‰ with respect to the initial CH2O that does not undergo photolysis. We also found that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotopic ratios as that of CH2O itself. These findings imply that there must be a strong isotopic fractionation in the radical channel (CH2O + h → CHO + H) compared to the molecular channel (CH2O + h → CO + H2). In the presentation we will discuss the results from the experiments focusing on how photochemical oxidation of CH4 may produce H2 enriched in deuterium.

2007-01-01T00:00:00Z