An infrared isotope analyzer

In a previous study of the fermentation of lactate by Clostridium lacto-acetophilum (Bhat and Barker, 1947) it was shown that pure cultures of this organism can decompose lactate only when acetate is provided as a second substrate, whereas enrichment cultures of the same organism do not require added acetate. This difference in nutritional requirements indicated a corresponding difference in the catabolic processes occurring in the two types of cultures. In pure cultures, lactate and acetate disappeared while butyric acid, carbon dioxide, and hydrogen were formed, whereas in enrichment cultures lactate was decomposed with the formation of acetate in addition to the other products. It is also significant that the yield of carbon dioxide was much lower in the enrichment cultures. The reduced yield of carbon dioxide taken in conjunction with the formation of acetate indicated that the organisms in the enrichment cultures were using carbon dioxide as an oxidant and were converting it to acetic acid. In pure cultures the high yield of carbon dioxide and the requirement for acetate indicated that the bacteria were unable to reduce carbon dioxide in this way. The tracer experiments described in the present paper were designed to provide a direct test of the conclusions derived from the above-mentioned nutritional and metabolic experiments.

For air‐water gas exchange across unbroken surfaces, the only gas‐dependent parameter affecting the transfer velocity is the molecular diffusivity of the transferring species. In contrast, bubble‐mediated transfer processes can cause the transfer velocity to depend on both molecular diffusivity and aqueous‐phase solubility. This can complicate the analysis of data from dual‐gaseous tracer gas transfer experiments. Bubble effects also complicate the estimation of transfer velocities for other gases from the transfer velocity calculated using the dual‐tracer data. Herein a method for incorporating the effects of bubble‐mediated gas transfer processes on the transfer velocity is presented. This new procedure is used to analyze the data from two recent dual‐tracer gas transfer experiments. Transfer velocities that include the effect of bubbles are calculated using the data from two previous oceanic dual‐gaseous tracer experiments. Comparing these transfer velocities with transfer velocities calculated by neglecting the effect of bubbles shows that bubble‐mediated transfer increased the transfer velocity of helium 3 by 5% at a wind speed of 10.6 m s−1. However, when using the transfer velocities for helium 3 to calculate transfer velocities for carbon dioxide under the same conditions, including the effect of bubbles decreases the transfer velocity of carbon dioxide by 18%. This shows that bubble‐mediated transfer does not have a large effect on the analysis of dual‐tracer data, but it is important in relating transfer velocities determined using helium 3 and sulfur hexafluoride to transfer velocities of more soluble gases at wind speeds above 10 m s−1.

In this dissertation the COmpact Carbon dioxide analyser for Airborne Platforms (COCAP) is presented. COCAP measures the abundance of carbon dioxide (CO2) in ambient air as well as air temperature, humidity and pressure, and is specifically designed for the use on board small unmanned aircraft systems (UASs). Accurate CO2 measurements are ensured by extensive calibration in an environmental chamber, by regular calibration in the field and by chemical drying of sampled air. In addition, the analyser is equipped with a custom-built, lightweight thermal stabilisation system that reduces the influence of ambient temperature changes on the CO2 sensor by two orders of magnitude. The robustness of COCAP under varying environmental conditions has been verified through a series of tests both in the lab and in the field. As a first application of the newly developed instrument, COCAP was used to constrain the nocturnal carbon dioxide emission of an ecosystem based on the nocturnal boundary layer (NBL) budget method. The NBL budgets were calculated from a series of CO2 profiles measured by COCAP on board a UAS during the course of two nights. The fluxes obtained in the pilot study are plausible and insensitive to experimental uncertainties. Given the versatility and moderate cost of UASs and their minimal infrastructure requirements, this innovative sampling technique makes the NBL budget method for the quantification of surface fluxes more accessible and cost-effective. This work demonstrates how the potential of UASs for measuring trace gases in theatmosphere can be exploited, thus opening up new possibilities for atmospheric research.

Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide

A common elemental analyzer system connected to a temperature-controlled gas chromatography (GC) column and coupled to an isotope ratio mass spectrometer was improved to decrease the determination limit for a simultaneous stable isotope ratio measurement of nitrogen and carbon dioxide. The additional use of a special ashtray system to collect the combustion residuals permitted more time-efficient work. These modifications to the elemental analyzer allowed precise measurements to be made down to 1.5 microg nitrogen and 10 microg carbon for stable isotope analysis. Low system background values and an acceptable signal-to-noise ratio have made an additional blank correction for these low sample measurements unnecessary. We provide a precision of this stable isotope analysis for lowest amounts of 1.2-2 microg nitrogen with a standard deviation of +/-0.496 per thousand (n = 27) and for 8.2-15 microg carbon with a standard deviation of +/-0.257 per thousand (n = 31) across different sample runs under stipulated conditions. This application can be established in an automatic mode without cryofocusing procedures.

Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide

The increasing application of 13C-labelled urea in medicine requires simple and reasonable methods for measuring highly enriched 13C in urea. The combination: ultimate organic analysis—mass spectrometry so far prescribed is complicated and expensive. For medical diagnosis, however, isotope selective nondispersive infrared spectrometers (NDIRS) have been available for many years. One of these tools is FANci2 which is very reasonable and easily to be operated. By means of such devices also urea highly enriched in 13C can be analysed, provided that the samples are first diluted with a defined amount of urea of natural isotopic composition and then transformed into carbon dioxide by means of urease. The relative abundance of 13C in this carbon dioxide, measured by nondispersive infrared spectrometry, is then a measure of the 13C abundance in the initial urea sample. Comparison of results of such measurements with those attained by mass spectrometry proves that this procedure is feasible and yields precise results.

The catalytic oxidation of propylene: X. An investigation of the kinetics and mechanism over USb 3O 10

Simultaneous local determination of mass transfer and residence time distributions in organic multiphase systems

The effect of radiocarbon on the rate of carbon dioxide utilization during photosynthesis

A newly developed isotope ratio laser spectrometer for CO2 analyses has been tested during a tracer experiment at the Ketzin pilot site (northern Germany) for CO2 storage. For the experiment, 500 tons of CO2 from a natural CO2 reservoir was injected in supercritical state into the reservoir. The carbon stable isotope value (δ(13)C) of injected CO2 was significantly different from background values. In order to observe the breakthrough of the isotope tracer continuously, the new instruments were connected to a stainless steel riser tube that was installed in an observation well. The laser instrument is based on tunable laser direct absorption in the mid-infrared. The instrument recorded a continuous 10 day carbon stable isotope data set with 30 min resolution directly on-site in a field-based laboratory container during a tracer experiment. To test the instruments performance and accuracy the monitoring campaign was accompanied by daily CO2 sampling for laboratory analyses with isotope ratio mass spectrometry (IRMS). The carbon stable isotope ratios measured by conventional IRMS technique and by the new mid-infrared laser spectrometer agree remarkably well within analytical precision. This proves the capability of the new mid-infrared direct absorption technique to measure high precision and accurate real-time stable isotope data directly in the field. The laser spectroscopy data revealed for the first time a prior to this experiment unknown, intensive dynamic with fast changing δ(13)C values. The arrival pattern of the tracer suggest that the observed fluctuations were probably caused by migration along separate and distinct preferential flow paths between injection well and observation well. The short-term variances as observed in this study might have been missed during previous works that applied laboratory-based IRMS analysis. The new technique could contribute to a better tracing of the migration of the underground CO2 plume and help to ensure the long-term integrity of the reservoir.

From measurements of the relative abundances of O- and CO3- ions produced in carbon dioxide by electron attachment and subsequent ion-molecule reactions, and from current-growth data, values of the primary ionization coefficient, attachment coefficient and rate coefficient for the reaction O-+2CO2 to CO3-+CO2 have been obtained for 60*10-17<E/N<152*10-17 V cm2 at gas number densities N between 0.2 and 5.0*1016 cm-3.

Estimation of Knudsen diffusion coefficients from tracer experiments conducted with a binary gas system and a porous medium

1317 In this paper we present the results of the experi� mental study of atmospheric brown clouds (ABC), which are congestions of polluted air on a regional scale consisting of large amounts of smallscale parti� cles of soot, sulfates, nitrates, soot dust, and other types of pollution (1, 2). The object of our research is smallscale particles that comprise the ABC of the Central Asia region, which were collected on the terri� tory of the highmountainous lidar complex Teplokly� uchenka belonging to the Kyrgyz-Russian Slavic University in the Central Tien Shan and at the Scien� tific Station of the Russian Academy of Sciences in Bishkek (SS RAS). The particles studied are charac� terized as nanoparticles (sizes from 1 to 1000 nm) and microparticles (size 1-1000 µm), which allows us to use the classification of particles based on their sizes. The nanoand microscale particles effectively influ� ence the screening of solar irradiance and scattering of the light in the atmosphere causing a decrease in visi� bility and disturbing the climatic balance (3). The brown shade of the ABC is caused by absorp� tion and scattering of the solar irradiance by the anthropogenic black carbon, soot dust, soil particles, and nitrogen dioxide. The atmospheric brown clouds are formed from anthropogenic and natural pollut� ants. At present, the developing countries of Asia, Africa, and South America suffer most of all from the pollutants released into the atmosphere, and black carbon, in particular. The most critical state is recorded in the Asian countries, in which the brown gas is especially dense. It spreads widely during the long dry season. Owing to this fact, the population of the region, in which more than 50% of the world pop� ulation lives, suffers from the negative influence of the brown gas on the health, hydrological cycle, and agri� culture (2). If we additionally take into account the role of the water and hydroenergetic resources in the formation of the economy of the Central Asian region, the problem of possible effects related to the ABC is one of the main strategic components of the national security of countries in this region (4). Despite the fact that the term "atmospheric brown clouds" became widely accepted only in the beginning of the 21st century, this phenomenon (without using this term) was actually noted already in September 1989 in the southwestern part of Tajikistan during a joint expedition of Soviet and American scientists (see, for example, (5-10)). In particular, they obtained results on the distribution of dust aerosol by size in the deserts of Central Asia (6) and demonstrated the significant role of the absorption of radiation in the optical range by black carbon during the formation of the radiation regime in the atmosphere (10). The influence of ABC on climate is particularly related to the incomparably greater efficiency of smallscale soot particles in the radiation processes than carbon dioxide, which is associated with an espe� cially important role in climatology. This is caused by the fact that absorption of radiation by smallscale soot particles is characterized by low selectivity. It is related to the entire wide range of solar irradiance but not to the narrow band of absorption by carbon diox� ide. It takes place (11) even if the concentration of crystal carbon in the atmosphere is only a few mil� lionths of the gaseous form of carbon dioxide and the productivity of its formation processes is significantly smaller than the productivity of carbon dioxide sources.

This work examinesthe stable isotope fractionation of carbon andoxygen in gaseous, supercritical, and liquid carbon dioxide systemsat temperatures from −27.1 to +43.5 °C. For pressurizedsingle-, supercritical-, and dual-phase carbon dioxide, both carbonand oxygen isotope fractionations can be measured and are significantwhen subjected to variations within this temperature range. The δ13C and δ18O values ranged from −41.55 to −41.38 ‰ (VPDB)and −27.74 to −24.9 ‰ (VPDB), respectively, forgas-phase carbon dioxide from 9.3 to 39 °C. A pressure variationof 27.58 barg to 34.48 barg was measured throughout this temperaturerange. In order to evaluate the effect of supercritical formationand liquefaction on the stable isotope values, cylinders were filledto varying pressures. When stored at cold temperatures, the δ13C value as measured in the headspace of the liquid phasevaried from −41.23 to −41.13 ‰ (VPDB) and −41.50to −41.44 ‰ (VPDB) in the supercritical phase. The δ18O value was between −25.51 and −25.36 ‰(VPDB) in the liquid phase and between −24.79 and −24.77‰ (VPDB) in the supercritical phase. Temperatures in theseexperiments were selected to mimic outdoor conditions (winter andsummer) that stable isotope laboratory practitioners may encounterwhen storing compressed carbon dioxide cylinders containing stableisotope working reference gases. The carbon and oxygen isotope compositionof carbon dioxide gas within these pressurized cylinders return totheir precooled isotope values within ∼24 h when warmed tolaboratory temperatures (∼24 °C). A headspace analysisperformed immediately after the carbon dioxide cylinder was removedfrom the cold environment yielded δ13C values thatwere relatively enriched, while δ18O values wererelatively depleted. This is likely an effect of 12C and 18O being preferentially partitioned in the liquid phase withinthe cylinder. As the cylinder warmed, both liquid and gas equilibrated,and carbon and oxygen homogenized isotopically. As the cylinder washeated into the supercritical phase, a slight opposite isotope effectat higher pressure and temperatures was noted. That is, a slight 13C depletion and 18O enrichment were observed inthe gas phase. However, these isotope variations were just slightlyoutside of the analytical error. Additionally, a separate gas-phasecarbon dioxide cylinder was kept at a constant laboratory temperatureas a control. This carbon dioxide showed no measurable carbon or oxygenisotope variation throughout the duration of the experimental work.The measured isotope fractionation was significantly higher comparingthe phase transition from the gaseous to liquid phase versus the gaseousphase to supercritical phase. The proper handling of pressurized carbondioxide cylinders used as reference gases for an isotope ratio massspectrometer includes using carbon dioxide at pressures of less than∼34.88 barg to ensure that the gas is present as a single phase,storing the gas in a temperature-controlled environment, and allowingthe gaseous carbon dioxide to equilibrate to ambient conditions for24–48 h if storage in a controlled ambient environment is notfeasible.