Role In Emissions Research Articles

Soil type links microbial colonization of rice roots to methane emission

AbstractMost of the methane (CH4) emission from rice fields is derived from plant photosynthates, which are converted to CH4. Rice cluster I (RC‐1) archaea colonizing the rhizosphere were found to be the methanogens responsible for this process. Hence, RC‐1 methanogens seem to play a crucial role in emission of the greenhouse gas CH4. We determined the community composition and activity of methanogens colonizing the roots of eight different rice cultivars after growth on both Italian rice soil and river bank soil, which contained different communities of methanogenic archaea. The community composition was analyzed by terminal restriction fragment length polymorphism and cloning/sequencing of the archaeal 16S rRNA gene and the mcrA gene coding for a subunit of the methyl coenzyme M reductase. When grown on rice field soil, the methanogenic community of the different rice cultivars was always dominated by RC‐1 methanogens. In contrast, roots were colonized by Methanomicrobiales when grown on river bank soil, in which RC‐1 methanogens were initially not detectable. Roots colonized with Methanomicrobiales compared with RC‐1 exhibited lower CH4 production and CH4 emission rates. The results show that the type of methanogens colonizing rice roots has a potentially important impact on the global CH4 cycle.

Physical wavelets and their sources: real physics in complex spacetime

For the first time, complete source distributions for the emission and absorption of acoustic and electromagnetic wavelets are defined and computed, both in spacetime and Fourier space. The biggest surprise is the great simplicity of the Fourier sources as compared to the rather convoluted spacetime expressions obtained from the original wavelets. This suggests that the associated pulsed-beam propagators may play a fundamental role in emission and absorption processes including focus or "directivity." It also opens the way to constructing FFT-based algorithms for pulsed-beam analyses of acoustic and electromagnetic waves.

Emissions trading in transition economies: the link between international and domestic policy

International emissions trading has the potential to significantly lower carbon mitigation costs and to promote environmentally friendly investment in transition economies. The design of domestic systems to complement international emissions trading will likely play a major role in emissions trading's effectiveness. This paper examines the benefits and challenges of proposed domestic systems and the related flows of emissions trading revenue in seller nations. The overwhelming majority of emissions available for sale will come from transition economies, which is why this article considers these countries as a group. Governments in countries such as Russia and Poland are interested in the potentially significant revenue they would reap from emissions trading, and some in those governments feel the money would best be used as general revenue for the government. Others argue that emissions trading should involve the private sector and other emitters in order to provide maximum incentives to reduce emissions and generate additional emissions trading revenue (the rules for international emissions trading explicitly allow this). Still others feel that special carbon mitigation funds would allow the government to maintain control yet stimulate additional emission reductions. Each policy contains its own set of challenges: stimulating further emission reductions, credibly monitoring emissions and emission reductions, or applying adequate fiscal accounting to the money flows.

Electron Acceleration and Time Variability of High‐Energy Emission from Blazars

Blazars are known to emit a broadband emission from radio to gamma rays with rapid time variations, particularly in X-rays and gamma rays. Synchrotron radiation and inverse Compton scattering are thought to play an important role in emission, and the time variations are likely related to the acceleration of nonthermal electrons. As simultaneous multiwavelength observations with continuous time spans have been recently available, some characteristics of electron acceleration can possibly be inferred from the spectral changes of high-energy emission. In order to make such inferences, we solve the time-dependent kinetic equations of electrons and photons simultaneously, using a simple model for electron acceleration. We then show how the time variations of emission are dependent on electron acceleration. We also present a simple model for a flare in X-rays and TeV gamma rays by temporarily changing the acceleration timescale. Our model can be used to analyze observed data in detail to obtain information on electron acceleration in blazars.

Relating Summer Ambient Particulate Sulfur, Sulfur Dioxide, and Light Scattering to Gaseous Tracer Emissions from the MOHAVE Power Project

ABSTRACT Project MOHAVE was initiated in 1992 to examine the role of emissions from the 1580 MW coal-fired MOHAVE Power Project (MPP) on haze at the Grand Canyon National Park (GCNP), located about 130 km north-northeast of the power plant. Statistical relationships were analyzed between summertime ambient concentrations of a gaseous perfluorocarbon tracer released from MPP and ambient SO2, particulate sulfur, and light scattering to evaluate whether MPP's emissions could be transported to the GCNP and then impact haze levels there. Spatial analyses indicated that particulate sulfur levels were strongly correlated across the monitoring network, regardless of whether the monitoring stations were upwind or downwind of MPP. This indicates that particulate sulfur levels in this region were influenced by distant regional emission sources. A significant particulate sulfur contribution from a point source such as MPP would result in a non-uniform pattern downwind. There was no suggestion of this in the data. Furthermore, correlations between the MPP tracer and ambient particulate sulfur and light scattering at locations in the park were virtually zero for averaging times ranging from 24 hr to 1 hr. Hour-by-hour MPP tracer levels and light scattering were individually examined, and still no positive correlations were detected. Finally, agreement between tracer and particulate sulfur did not improve as a function of meteorological regime, implying that, even during cloudy monsoon days when more rapid conversion of SO2 to par-ticulate sulfur would be expected, there was no evidence for downwind particulate sulfur impacts. Despite the fact that MPP was a large source of SO2 and tracer, neither time series nor correlation analyses were able to detect any meaningful relationship between MPP's SO2 and tracer emission “signals” to particulate sulfur or light scattering.

Comments on “Relating Summer Ambient Particulate Sulfur, Sulfur Dioxide, and Light Scattering to Gaseous Tracer Emissions from the MOHAVE Power Project”

ABSTRACT Project MOHAVE was initiated in 1992 to examine the role of emissions from the 1580 MW coal-fired MOHAVE Power Project (MPP) on haze at the Grand Canyon National Park (GCNP), located about 130 km north-northeast of the power plant. Statistical relationships were analyzed between summertime ambient concentrations of a gaseous perfluorocarbon tracer released from MPP and ambient SO2, particulate sulfur, and light scattering to evaluate whether MPP's emissions could be transported to the GCNP and then impact haze levels there. Spatial analyses indicated that particulate sulfur levels were strongly correlated across the monitoring network, regardless of whether the monitoring stations were upwind or downwind of MPP. This indicates that particulate sulfur levels in this region were influenced by distant regional emission sources. A significant particulate sulfur contribution from a point source such as MPP would result in a non-uniform pattern downwind. There was no suggestion of this in the data. Fur...

Reliability of the current models of instantaneous pollutant emissions

Pollutant emissions and fuel consumption of passenger cars are usually assessed as a function of average speed. Nevertheless a number of attempts were made to take into account the driving pattern using emission vs. instantaneous speed and acceleration models. Five quite similar models were developed in Europe. To which extent these instantaneous models are innovative as compared to conventional models? In a first step the various development stages of an emission-based model and the various associated errors are presented. Among the possible sources of error, we selected modelling-induced errors, enabling to compare rigorously the various model types in terms of performance. The analysis was performed using the Modem model, developed from the measurement results obtained over a sample of 150 vehicles, representative of French, English and German fleets, over 14 representative driving cycles under urban conditions. Average emissions as measured over these 14 cycles are compared to emissions calculated over same cycles using this model. Modelling errors range from −51% to +57% as a function of the considered cycle and the vehicle type. This inaccuracy is quite similar for the other four European models. This demonstrates the low reliability of the models used, which cannot be used to assess the impact of slight changes in the driving pattern, sometimes leading to completely false conclusions. These models are barely more precise than average speed based models. In a second step, a number of alternatives liable to improve the reliability of instantaneous models are contemplated: for example using another method for calculating acceleration, or increasing the number of speed and acceleration classes significantly. But this does not improve significantly the model reliability. Limited measurements performed on a catalyst vehicle demonstrated that very high engine loads, even if not frequent, play a significant role in emissions: sometimes they yield emission values a thousand times higher. It is therefore of prime interest to study them in a comprehensive manner. In addition, this demonstrates that each model should be developed from measurements carried out over a set of representative driving cycles under real-world driving conditions.

Low Energy Electron Emission in a Pure Three Body Collision: C6+ + H

We have investigated the energy and angular distributions of the low energy electron emission in a pure three-body ion-atom collision involving atomic hydrogen as target. The double differential ionization cross sections have been measured for C6+ + H (v = 6–10 a.u.). The CDW-EIS calculations provide an excellent agreement with the data except some discrepancies in the backward angles. These observations clearly show that the two center mechanism plays a major role in emission of low energy electrons.

Pollution sources and spreading of sulphur dioxide in the North-Eastern Estonia

The greatest sources of atmospheric emissions of SO2 in Estonia are caused by power plants (TP) which use oil shale. Since 1990 the amount of SO 2 discharges has continuously decreased due to fall in production of electric energy, and it was from TP as follows: in 1990–1991 about 180–200 thousand tons, in 1992 about 140 and in 1993–1994 about 100 thousand tons. In 1990 the annual mean emission intensity of SO 2 from all North-East (NE) Estonian pollution sources was fixed to be about 6.kg/s, with a maximum of 9.5–11 kg/s in winter period. In 1992–1993 the corresponding values were 3.5–4.6 and 5.1–6.8 kg/s. The single maximum concentrations (MC, per 30 min.) of SO 2 in the overground air layer would be in the ranges 25–450 μg/m 3 depending on emission intensity and wind parameters. The annual mean concentrations are below 25 μg/m 3 on the main territory, but may be up to 50–75 μg/m 3 near the power plants. In Kohtla-Jarve town the annual mean values of 15.8–19.1 μg/m 3 and MC values of 271–442 μg/m 3 were fixed during 1991–1994 by automatic air monitoring system. Many arable lands, forest areas and wild-life preserves are subjected to relatively high sulphur precipitation loads, exceeding 0.5 g S/m2 per year, of which the role of emissions from local sources is about 60–95%. On the basis of air pollution concentration maps, the landscape of NE Estonia is classified into zones of high, moderate and low pollution level.

Laser processes and energy transfers

The effect of the energy transfer processes on the population kinetics of laser levels in systems with one type of activator is discussed. It is shown that while for some laser systems the energy transfer is an efficiency limiting factor, for others it plays an essential role in emission. Some recent results on two important laser systems YAG:Nd and YAG:Er are discussed.

The role of motor vehicles in air pollution in the UK

This paper presents an overview of the contribution of motor vehicles to some air pollution issues in the UK. The coverage of issues is selective concentrating primarily on the motor vehicle's role in emissions of carbon dioxide and other greenhouse gases, NO x concentrations in rural and urban areas. Finally some discussion is given of future technological developments in vehicle pollution control technology and some possible air pollution consequences.

Stimulated Compton conversion of Langmuir waves by relativistic electron beams

Stimulated inverse Compton conversion in which a Langmuir wave scatters off a relativistic electron while converting into a transversely polarized electromagnetic wave is considered as a means for producing amplified electromagnetic radiation from a beam-plasma system at frequencies well above the electron plasma frequency. The stimulated emission growth rates of the radiation produced by a monoenergetic ultrarelativistic electron beam are determined as a functional of the Langmuir turbulence spectrum in the background plasma and are numerically evaluated for a range of model Langmuir spectra. Stimulated inverse Compton conversion can play a role in emission from astrophysical beam-plasma systems if the electron beam is highly relativistic and sufficiently narrow. However, it is found that the growth rates for this process are too small in all cases studied to account for the intense high-frequency radiation observed in the laboratory experiments of G. Benford et al. [G. Benford, D. Tzach, K. Kato, and D. F. Smith, Phys. Rev. Lett. 45, 1182 (1980); K. G. Kato, G. Benford, and D. Tzach, Phys. Rev. Lett. 50, 1587 (1983); K. G. Kato, G. Benford, and D. Tzach, Phys. Fluids 26, 3636 (1983)].

On the emission mechanism of oxide cathodes

The emission mechanism of oxide cathodes is discussed through bulk donor concentration, electrical conductivity, activation, compositions and uniformity of emission. The existing semiconductor model encounters difficulties in explaining these experimental facts consistently and a model of a dynamical surface emission centre is proposed to invoke discussions, in this new model, emission comes from such an aggregate of surface atoms that the moving electrons may have momentarily high energy and at the same time the potential field due to the neighbouring nuclei reaches a minimum. Oxygen may play a favourable or unfavourable role in emission depending on its relative quantity and relative position in the aggregate. The function of SrO and CaO is to help adsorbtion of Ba and pass the electron from the base metal to emission sites. Diffusion, migration, evaporation, poisoning and sputtering cause these centres to vary frequently

Structure of the heating layer ahead of the front of a strong intensely emitting shock wave

The problem of the structure and brightness of strong shock waves arises in the investigation of such phenomena as the motion of large meteoroids in the atmosphere, optical and electrical discharges, the development of strong explosions, and other similar processes and in the creation of powerful radiation sources based on them. This problem also has a general physics interest. As the propagation velocity of a strong shock wave increases the gas temperature behind its front and the role of emission grow. Part of the radiation emitted by the gas heated and compressed in a shock wave is absorbed ahead of the front, forming the so-called heating layer. The quasisteady structure of a strong intensely emitting shock wave was studied in [1, 2]. In this case a diffusional approximation and the assumption of a gray gas were used to describe the radiation transfer. They introduced the concept of a wave of critical amplitude, when the maximum temperature T- in the heating layer reaches the temperature Ta determined on the basis of the conservation laws, i.e., from the usual shock adiabat; it is shown that behind a compression shock moving through an already heated gas there is a temperature peak in which the maximum temperature T+ exceeds Ta. The problem of the quasisteady structure of an emitting shock wave in air of normal density was solved numerically in [3]. The angular distribution of the radiation was approximately taken into account — it was assigned by a simple cosinusoidal law. The spectral effects were taken into account in a multigroup approximation. They introduced 38 spectral intervals, which is insufficient to describe a radiation spectrum with allowance for the numerous lines and absorption bands.

Quantum Field Theory of Interacting Tachyons

A quantum field theory of spin-0 particles traveling with speeds greater than that of light has been constructed. The theory constructed here is explicitly Lorentz-invariant; and the quanta of the field obey Bose statistics. Formalism developed for the free field has been extended to the case of interaction of these particles with nucleons. A new feature of theory is the occurrence of negative-energy particles; this is a necessary consequence of the relativistic invariance of the theory, since the distinction between positive and negative energies is not a relativistically invariant concept for such particles. The occurrence of these negative-energy particles does not, however, prevent the theory from being meaningful; the physical interpretation of the situation is provided by the postulate that any process involving negative-energy particles is to be identified with a physical process with only positive-energy particles traveling in the opposite direction, with the roles of emission and absorption interchanged. The scattering amplitudes are the same as in the usual theory with ${m}^{2}$ replaced by $\ensuremath{-}{m}^{2}$.