Major Source Of CO2 Research Articles

The significance of agricultural sources of greenhouse gases

The impact of development of land for agriculture and agricultural production practices on emissions of greenhouse gases is reviewed and evaluated within the context of anthropogenic radiative forcing of climate. Combined, these activities are estimated to contribute about 25%, 65%, and 90% of total anthropogenic emissions of CO2, CH4, and N2O, respectively. Agriculture is also a significant contributor to global emissions of NH3, CO, and NO. Over the last 150 y, cumulative emissions of CO2 associated with land clearing for agriculture are comparable to those from combustion of fossil fuel, but the latter is the major source of CO2 at present and is projected to become more dominant in the future. Ruminant animals, rice paddies, and biomass burning are principal agricultural sources of CH4, and oxidation of CH4 by aerobic soils has been reduced by perturbations to natural N cycles. Agricultural sources of N2O have probably been substantially underestimated due to incomplete analysis of increased N flows in the environment, especially via NH3 volatilization from animal manures, leaching of NO3-, and increased use of biological N fixation.

Automotive Fuel Efficiency

For at least the remainder of this century, the United States faces a growing dependence on imported oil. Costs are substantial, and they will mount. In June 1992, net imports provided nearly 50% of supplies, and their cost was $4.3 billion. Cost of net imports of motor vehicles and parts amounted to $3.0 billion. The two items combined totaled more than the negative trade balance of $6.6 billion. The light-duty highway fleet alone accounted for 38.2% of U.S. oil consumption in 1988. Correspondingly, the fleet was a substantial emitter of air pollutants - NO{sub x}, CO, and nonmethane hydrocarbons. In addition, it was a major source of CO{sub 2}. The twin problems of oil imports and pollution would be ameliorated if the fuel economy if cars and trucks could be improved and their emissions were also reduced. In principle, the mileage of US automobiles could be substantially improved. But on purchasing a car, U.S. buyers rank fuel efficiency eight when making their choice. They are attracted to options that lower mileage. Consumers also tend to prefer large cars over small ones for reasons of safety. Increasingly, buyers are purchasing light trucks and vans that have inferior fuel efficiency. As amore » result of the above trends, the average mileage of the US automotive fleet has been diminishing. As long as fuel is available at comparatively low prices and there is no federal requirement for better mileage, improvement is unlikely. Moreover, even if improvements were mandated, change would be slow.« less

Source of Respiratory Carbon Evolved from the Shoots of Rice Seedlings in Darkness.

The time course change of the shoot respiration rate, the percentage of currently assimilated carbon in respiration and the amounts of current and reserved compounds in the shoots of rice plants were examined using the steady-state 13CO2 assimilation technique, in an attempt to evaluate the change of respiratory substrates with time during darkness. The shoot respiration exhibited midnight rise of respiration rate (MRR), and then a sudden decrease around 13 hours after the onset of darkness. The percentage of CO2 derived from 13C-labeled current assimilates in respiration was high during the first 6 hours, and followed by a continuous decrease. Therefore, current assimilates took priority over reserved compounds to support midnight respiration with MRR in the dark period, and as being consumed current photosynthates the respiration using reserved materials increased to compensate the respiration. Since the 13C-labeling and the content of sucrose were high during the early dark period, it was suggested that sucrose was the principal source of respiratory substrates, and thereafter, starch and other compounds gradually became the major source of CO2. The integrated value of the percentage of 13C-labeled CO2 in total respired CO2 during the first 12 hours was 51%, suggesting respiration dependency on current assimilates was almost equivalent to that on reserved materials.

Air quality in the vicinity of urban roads

Motor vehicle emissions are a major source of CO, NO x and lead particulate concentrations to urban air quality. London urban Boroughs with high traffic densities are therefore a particular cause for concern. The air quality was monitored at an urban background site in the London Borough of Haringey for 2-years. The results of this study are assessed and their effect on human health is considered in the light of EC Directives and WHO guidelines. A desk top modelling technique based on Gaussian diffusion theory was used to predict the CO levels found at the background site. All predicted levels had a accuracy of better than 30%.

The radiative association of C and O and C(+) and O

The formation of CO(+) and CO in the expanding metal-rich ejecta of SN 1987A has been discussed by Lepp et al. (1988) and by Petuchowski et al. (1989), who concluded that it probably proceeded through the radiative association of C(+) and O to form CO(+) by the reactions (1) C(+) + O - CO(+) + hnu, followed by charge transfer of CO(+) with O, (2) CO(+) + O - CO + O(+), and by the radiative association of C and O to form CO, (3) C + O - CO + hnu. Petuchowski et al. estimated the rate coefficients of reactions (1) and (3) and concluded that the sequence of (1) and (2) constitutes the major source of CO. An alternative calculation of the rate coefficients is made here that indicates that reaction (3) is probably more important. 36 refs.

Latitudinal distribution of the sources and sinks of atmospheric carbon dioxide derived from surface observations and an atmospheric transport model

Determination of the present global budget of atmospheric carbon dioxide (CO2) from the small and persistent concentration gradients that exist in the atmosphere is discussed. The CO2 concentration at any site results from a combination of two factors: local sources or sinks and long‐range transport. To separate these two effects, an atmospheric transport model is needed. The extensive sets of global CO2 measurements of the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Monitoring for Climatic Change (GMCC) division and of the Upper Atmosphere and Space Research Laboratory of Tohoku University are combined with a two‐dimensional transport model to derive, in an “inverse” calculation, the latitudinal and seasonal distributions of sources and sinks of CO2 necessary to reproduce the observed concentrations. The model transport parameters were previously derived from a three‐dimensional general circulation model. It is found that the southern oceans are a sink of carbon of 0.8–1.5 Gt yr−1 (1 Gt equals 1015g) and that the equatorial areas are a source to the atmosphere of 1.4–2.8 Gt yr−1. Tropical deforestation as a major source of CO2 must be smaller than that because the oceans account for a significant part of the equatorial flux. There seems to be significant seasonality in the sources and sinks of CO2, both in the tropics and in the southern oceans. The seasonal net ecosystem production north of 25°N is found to be 6.2–8.2 Gt of carbon, but these estimates are probably somewhat too low. The source deduction problem is difficult to solve, especially for the middle and high latitudes in the northern hemisphere. This is due to a lack of observations over the continents, which occupy more than half of the global area at these latitudes and are the regions where the sources and sinks are most intense. Evidence is found in the results obtained for the GMCC and Tohoku data that the longitudinal variability of the data is large enough, even in equatorial and southern latitudes, to prevent a two‐dimensional model from calculating a fully credible source/sink field. The longitudinal variations in the observations have to be accounted for with a three‐dimensional transport model.

Carbon cycling by cellulose-fermenting nitrogen-fixing bacteria

The most abundant organic materials on Earth are plant polysaccharides such as cellulose and hemicelluloses. Inasmuch as vast quantities of these polymers are present in anaerobic environments (e.g., in soils and sediments), anaerobic microorganisms that ferment plant polysaccharides play a central role in carbon cycling on the planet as a source of CO 2 and, indirectly, of CH 4. Cellulose-fermenting bacteria from soil and pond sediment were isolated in a medium (incubated in N 2) which lacked a source of combined nitrogen. The isolates had the ability to utilize atmospheric N 2 as the nitrogen source for cell growth. Nitrogenase (the enzyme which catalyzes the reduction of N 2 to ammonia) was demonstrated by means of the acetylene reduction test in these isolates and in several previously described anaerobic cellulolytic bacteria isolated from various natural environments. Thus, cellulose-fermenting bacteria that fix N 2 may be widespread and may play a role in nitrogen cycling as well as in carbon cycling on a global scale. Knowledge of the physiology and ecology of these organisms is crucial to detailing the mechanisms producing local sources and sinks of atmospheric gases, interpreting data obtained using space-based sensors, and understanding the effects of atmospheric warming on fermentations as major sources of CO 2 and CH 4.

Supercritical water/CO liquefaction and a model for coal conversion

Studies of Illinois No. 6 coal in CO/water at 400°C over a range of conversions to toluene-soluble (TS) products show product yields in D 2O consistently superior to those in H 2O, the yields leveling off respectively at 60% and 50%. These findings are compelling toward a conversion scheme in which coal is partitioned in parallel, competitive steps to TS and toluene insoluble (TI) fractions, with the TS/TI ratio determined by the reduction potential of the system. Conversion is thus limited by the kinetics of conversion rather than by coal structure, this limitation applying to conversion generally, including conventional donor conversions. The CO/water system has been successfully modeled with a numerical simulation scheme on a microcomputer, the model showing that the key limiting feature of the CO/water system is irreversible consumption of OH − by CO 2. The major source of CO 2 is the water gas shift reaction, which operates in parallel to the conversion chemistry.

Stable-isotopic composition of soil carbon dioxide in the Tucson basin, Arizona, U.S.A.

Most models to correct 14C groundwater ages require the δ 13C-value of soil CO 2 in the recharge areas of the aquifer at the time of recharge. Ninety-one soil gas samples were collected at three long-term sites in the Tucson area from July 1980 to June 1981 to determine the extent of seasonal variations and the influence of vegetation on the δ 13C and CO 2 concentration of soil gases. Variations were observed in both δ 13C and CO 2 concentrations. The highest CO 2 concentrations, up to 1.3% at 60-cm depth, were observed during March and April; the lowest, 0.1% CO 2 at 12-cm depth, were observed during the winter months. The δ 13C-values varied by ~ 5‰ during the sampling period. The lowest 13C contents were found in early spring and summer. Part of the δ 13C variation is due to exchange with atmospheric CO 2. Other causes could be decomposition of organic matter with different isotopic composition and different decay rates and/or to a seasonal displacement of the period of maximum activity among different varieties of plants. The mean δ 13C for samples at the long-term sites was ~ −18‰. In addition, fifteen soil gas samples were collected in the bottom of washes which are the assumed recharge areas of the Tucson aquifer. Both CO 2 and 13C concentrations showed changes with time and location. High concentrations of CO 2 of up to 4.8% were found. The mean δ 13C for these samples was ~ −20‰. A major source of CO 2 in the riverbeds is believed to be decomposition of organic matter carried out by the runoff water during the periodic flooding of the washes.

Malic Acid as a Source of Carbon Dioxide in Cucumber Juice Fermentations

ABSTRACTThe degradation of malic acid to lactic acid and CO2 during fermentation of cucumber juice was investigated. This malolactic reaction was the major source of CO2 when cucumber juice was fermented by Lactobacillus plantarum. It may also be an important CO2 source in controlled cucumber fermentations. In addition to CO2 production, the degradation of malate served to buffer the fermentation and increase sugar utilization. The pH after 7 days’fermentation was 2.8 when 13 mM malic acid was present in the juice and 4.1 with 135 mM malic acid. In the same fermentations, 52% of the sugars were degraded with the low malic acid concentration while complete sugar utilization was observed with the highest malic acid level.

The origin of chloroplastic acetyl coenzyme A

Pyruvic dehydrogenase activity has been examined in a number of highly purified leaf organelles. In spinach leaf cell, the major activity is in the mitochrondrion with low activity in isolated chloroplasts. The major source of CO 2 derived from pyruvic acid metabolism in the isolated chloroplast is via the acetolactic synthase reaction localized in the chloroplast. Evidence is presented that the leaf mitochondrion contains both the pyruvic acid dehydrogenase and an acetyl coenzyme A hydrolase. It is suggested that free acetic acid is generated in the mitochrondrion and then moves to the chloroplast where acetyl coenzyme synthetase converts it from the metabolically inert acid to the very metabolically active acetyl coenzyme A.

Stable carbon isotopes of HCO 3− in oil-field waters—implications for the origin of CO 2

The δ 13C values of dissolved HCO 3 − in 75 water samples from 15 oil and gas fields (San Joaquin Valley, Calif., and the Houston-Galveston and Corpus Christi areas of Texas) were determined to study the sources of CO 2 of the dissolved species and carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The reservoir rocks are sandstones which range in age from Eocene through Miocene. The δ 13C values of total HCO 3 − indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin. The range of δ 13C values for the HCO 3 − of these waters is −20–28 per mil relative to PDB. This wide range of δ 13C values is explained by three mechanisms. Microbiological degradation of organic matter appears to be the dominant process controlling the extremely low and high δ 13C values of HCO 3 − in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low δ 13C values (< −10 per mil) are obtained in waters where concentrations of SO 4 2− are more than 25 mg/l and probably result from the degradation of organic acid anions by sulfate-reducing bacteria ( SO 4 2− + CH 3 COO − → 2 HCO 3 − + HS −). The high δ 13C values probably result from the degradation of these anions by methanogenic bacteria ( CH 3 COO − + H 2 O ai HCO 3 − + CH 4). Thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO 2 and CH 4 is probably the major source of CO 2 for production zones with subsurface temperatures greater than 80°C. The δ 13C values of HCO 3 − for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO 2 and CH 4. At these high temperatures, δ 13C values of HCO 3 − decrease with increasing temperatures and decreasing concentrations of these acid anions.

Climate models and CO2-induced climatic changes

This article is a review of the modeling of potential CO2 effects on climate, intended for an interdisciplinary audience of ‘mathematically oriented’ scientists and engineers. The carbon dioxide (CO2) content of the atmosphere has shown a systematic increase each year since regular measurements began in 1958. A major source of CO2 is the combustion of fossil fuels. A number of studies of the sensitivity of climate to increases in the CO2 content of the atmosphere have been published. This report is an assimilation of the results of some of these studies. The climate sensitivity problem is introduced through a discussion of the various atmospheric feedbacks and the ice albedo feedback. The most recent estimates of the various feedbacks are used to estimate upper and lower bounds of the globally averaged temperature increase that would accompany a doubling of atmospheric CO2 content. The results of a CO2 doubling experiment using a simple general circulation model are reviewed, and the possible response of the cryosphere is discussed.

Stable Carbon Isotopes in Oil-Field Waters and Origin of Carbon Dioxide: ABSTRACT

The ^dgr13C values of dissolved HCO3- in 75 water samples from 15 oil and gas fields were determined in a study of the source of carbon dioxide of the dissolved species and the carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The fields are located in the San Joaquin Valley, California, and the Houston-Galveston and Corpus Christi areas of Texas. The reservoir rocks are sandstones ranging in age from Eocene through Miocene. The ^dgr13C values of total HCO3- indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin. The range of ^dgr13C values for the HCO3- of these waters is -20 to 28 permit relative to the PDB standard. This wide range of values is explained by three mechanisms. Microbiologic degradation of organic matter appears to be the dominant process controlling the extremely low and high ^dgr13C values (-20 to 28 per-mil) of HCO3- in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low ^dgr13C values are obtained in waters where the concentration of SO4 is more than 25 mg/L and probably result from the degradation of organic acid anions by sulfate-reducing bacteria (SO42- + CH3COO- ^rarr 2HCO3- + HS-). The high ^dgr13C values probably result from the degradation of acetate by methanogenic bacteria (CH3COO- + H2O^rlarrHCO3- + CH4). For samples from production zones with subsurface temperatures greater than 80°C, thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO2 and CH4 is probably the major source of CO2. The ^dgr3C values of HCO3- for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO2 and CH4. At these high temperatures, ^dgr13C values of HCO3- decrease with increasing temperatures and decreasing concentrations of these acid anions. End_of_Article - Last_Page 479------------

Carbon Dioxide Fixation by Lupin Root Nodules

In vivo CO(2) fixation and in vitro phosphoenolpyruvate (PEP) carboxylase levels have been measured in lupin (Lupinus angustifolius L.) root nodules of various ages. Both activities were greater in nodule tissue than in either primary or secondary root tissue, and increased about 3-fold with the onset of N(2) fixation. PEP carboxylase activity was predominantly located in the bacteroid-containing zone of mature nodules, but purified bacteroids contained no activity. Partially purified PEP carboxylases from nodules, roots, and leaves were identical in a number of kinetic parameters. Both in vivo CO(2) fixation activity and in vitro PEP carboxylase activity were significantly correlated with nodule acetylene reduction activity during nodule development. The maximum rate of in vivo CO(2) fixation in mature nodules was 7.9 nmol hour(-1) mg fresh weight(-1), similar to rates of N(2) fixation and reported values for amino acid translocation.The results suggest that the oxaloacetete used as the primary "carbon skeleton" acceptor for ammonia assimilation and amino acid synthesis in lupin nodules is provided via the PEP carboxylase reaction rather than through the tricarboxylic acid cycle. The source of PEP is presumably glycolysis, while the major source of CO(2) is inferred to be respiration.

Photochemistry of minor constituents in the troposphere

Altitude profiles for the number densities of NO, NO 2, NO 3, N 2O 5, HNO 2, CH 3O, CH 3O 2, H 2CO, OH, and HO 2 are calculated as a function of time of day with a steady-state photochemical model in which the altitude profiles for the number densities of H 2O, CH 4, H 2, CO, O 3, and the sum of NO and NO 2 are fixed at values appropriate to a summer latitude of 34°. Average daily profiles are calculated for the long-lived species, HNO 3, H 2O 2, and CH 3O 2H. The major nitrogen compound HNO 3 may have a number density approaching 5 × 10 11 molecules cm −3 at the surface, although an effective loss path due to collisions with particulates could greatly reduce this value. The number density of OH remains relatively unchanged in the first 6 km and reaches 1 × 10 7 molecules cm −3 at noon, while the number density of HO 2 decreases throughout the lower troposphere from its noontime value of 8 × 10 8 molecules cm −3 at the surface. H 2O 2 and H 2CO both have number densities in the ppb range in the lower troposphere. Owing to decreasing temperature and water concentration, the production of radicals and their steady-state number densities decrease with altitude, reaching a noontime minimum of 1 × 10 8 molecules cm −3 for OH and 3 × 10 7 molecules cm −3 for HO 2 at the tropopause. The related minor species show even sharper decreases with increasing altitude. The primary path for interconverting OH and HO 2 serves as the major sink for CO and leads to a tropospheric lifetime for CO of ~0.1 yr. Another reaction cycle, the oxidation of CH 4, is quite important in the lower troposphere and leads to the production of H 2CO along with the destruction of CH 4 for which a tropospheric lifetime of ~2 yr is estimated. The destruction of H 2CO that was produced in the CH 4 oxidation cycle provides the major source of CO and H 2 in the atmosphere.