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New expressions for the wavelength-dependent photolysis quantum yields of CH2O, Φj, are presented. They are based on combinations of functions of the type Ai/(1+exp[-(1/λ - 1/λ0i)/bi]). The parameters Ai, bi, and λ0i which have a physical meaning, are obtAined by fits to the measured Φj data avAilable from literature. The altitude dependence of the photolysis frequencies resulting from the new quantum yield expressions are compared to those derived from the Φj recommended by JPL and IUPAC. [ABSTRACT FROM AUTHOR]

ABSTRACT In the past two types of laboratory experiments have been employed to determine the dependence of H2 uptake by soils on temperature and moisture: Head space and flow experiments. The former actually measure the rate constant of the H2 removal from the head space, kH, the latter the uptake rate of H2, UH2, both caused by a given volume of soil. From an analytical solution of the diffusion equation in the soil we derive a mathematical relation between kH and ks, the desired uptake rate constant of H2 in soil. Another equation relates UH2 with ks. Both types of experiments actually determine the product of ks with Θa, the air-filled pore volume fraction. ks·Θa for eolian sand and loess loam show zero uptake at very low and high moisture contents and a well defined maximum in between. Unlike soil moisture which also acts on the soil properties, the soil temperature, T, acts essentially on the enzyme activity only. Thus ks( T) is directly proportional to kH( T) or UH2( T) and the data of all experiments can be superimposed by scaling. The resulting average ks( T) shows a broad maximum around 30°C with zero uptake below −20°C and above 80°C. [ABSTRACT FROM AUTHOR]

The literature on the distribution, budget and isotope content of molecular hydrogen (H2) in the troposphere is critically reviewed. The global distribution of H2 is reasonably well established and is relatively uniform. The surface measurements exhibit a weak latitudinal gradient with 3% higher concentrations in the Southern Hemisphere and seasonal variations that maximize in arctic latitudes and the interior of continents with peak-to-peak amplitudes up to 10%. There is no evidence for a continuous long-term trend, but older data suggest a reversal of the interhemispheric gradient in the late 1970s, and an increase in the deuterium content of H2 in the Northern Hemisphere from 80‰ standard mean ocean water (SMOW) in the 1970s to 130‰ today. The current budget analyses can be divided in two classes: bottom up, in which the source and sink terms are estimated separately based on emission factors and turnovers of precursors and on global integration of regional loss rates, respectively. That category includes the analyses by 3-D models and furnishes tropospheric turnovers around 75 Tg H2 yr−1. The other approach, referred to as top down, relies on inverse modelling or analysis of the deuterium budget of tropospheric H2. These provide a global turnover of about 105 Tg H2 yr−1. The difference is due to a much larger sink strength by soil uptake and a much larger H2 production from the photochemical oxidation of volatile organic compounds (VOC) in the case of the top down approaches. The balance of evidence seems to favour the lower estimates—mainly due to the constraint placed by the global CO budget on the H2 production from VOC. An update of the major source and sink terms yields: fossil fuel use 11 ± 4 Tg H2 yr−1; biomass burning (including bio-fuel) 15 ± 6 Tg H2 yr−1; nitrogen fixation (ocean) 6 ± 3 Tg H2 yr−1; nitrogen fixation (land) 3 ± 2 Tg H2 yr−1; photochemical production from CH4 23 ± 8 Tg H2 yr−1 and photochemical production from other VOC 18 ± 7 Tg H2 yr−1. The loss through reaction of H2 with OH is 19 ± 5 Tg H2 yr−1, and soil uptake Tg H2 yr−1. All these rates are well within the ranges of the corresponding bottom up estimates in the literature. The total loss of 79 Tg H2 yr−1 combined with a tropospheric burden of 155 Tg H2 yields a tropospheric H2 lifetime of 2 yr. Besides these major sources of H2, there are a number of minor ones with source strengths <1 Tg H2 yr−1. Rough estimates for these are also given. [ABSTRACT FROM AUTHOR]

MIPAS, the Michelson Interferometer for Passive Atmospheric Sounding, is a mid-infrared emission spectrometer which is part of the core payload of ENVISAT. It is a limb sounder, i.e. it scans across the horizon detecting atmospheric spectral radiances which are inverted to vertical temperature, trace species and cloud distributions. These data can be used for scientific investigations in various research fields including dynamics and chemistry in the altitude region between upper troposphere and lower thermosphere. The instrument is a well calibrated and characterized Fourier transform spectrometer which is able to detect many trace constituents simultaneously. The different concepts of retrieval methods are described including multi-target and two-dimensional retrievals. Operationally generated data sets consist of temperature, H2O, O3, CH4, N2O, HNO3, and NO2 profiles. Measurement errors are investigated in detail and random and systematic errors are specified. The results are validated by independent instrumentation which has been operated at ground stations or aboard balloon gondolas and aircraft. Intercomparisons of MIPAS measurements with other satellite data have been carried out, too. As a result, it has been proven that the MIPAS data are of good quality. MIPAS can be operated in different measurement modes in order to optimize the scientific output. Due to the wealth of information in the MIPAS spectra, many scientific results have already been published. They include intercomparisons of temperature distributions with ECMWF data, the derivation of the whole NOy family, the study of atmospheric processes during the Antarctic vortex split in September 2002, the determination of properties of Polar Stratospheric Clouds, the downward transport of NOx in the middle atmosphere, the stratosphere-troposphere exchange, the influence of solar variability on the middle atmosphere, and the observation of Non-LTE effects in the mesosphere. [ABSTRACT FROM AUTHOR]

This article reports on the increasing amount of methane in the atmosphere and its possible impact on the climate as of December 1, 1985. Methane is a colorless, odorless trace gas found throughout the Earth's atmosphere. Even at low concentrations, methane has a significant role in the overall chemistry of the atmosphere. Recently recognized increases in methane levels carry potentially important consequences that are only beginning to be understood. Research findings did not raise much interest within the scientific community because methane is not a noxious gas and was considered to be chemically inert in the troposphere. Not until the 1970s did methane attract attention when new interest arose from research on the impact of trace gases on stratospheric ozone. It was recognized that methane accounts for a very substantial portion of stratospheric hydrogen. In fact, it contributes about 50 percent to the budget of hydrogen compounds in the stratosphere. But particularly intriguing is the most recent finding of an increase in atmospheric methane of about 1 to 2 percent per year. Because methane is a gas that absorbs infrared radiation, contributing to the greenhouse effect, its increase has climatic implications. INSET: Methane: The Microbial Source.