Atmospheric Chemistry (atmospheric + chemistry)

Distribution by Scientific Domains

Selected Abstracts

ChemInform Abstract: New Molecular Species of Potential Interest to Atmospheric Chemistry: Isomers on the [H, S2, Br] Potential Energy Surface

CHEMINFORM, Issue 17 2009
Antonio Gustavo S. de Oliveira-Filho
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Identification of the D3h Isomer of Carbon Trioxide (CO3) and Its Implications for Atmospheric Chemistry

CHEMPHYSCHEM, Issue 12 2006
Corey S. Jamieson
Abstract The CO3 molecule is considered an important reaction intermediate in the atmospheres of Earth and Mars for quenching electronically excited oxygen atoms and in contributing to the anomalous 18O isotope enrichment. The geometry of the CO3 intermediate plays an important role in explaining these effects; however, only the cyclic (C2v) isomer has been experimentally confirmed so far. Here, we report on the first spectroscopic detection of the acyclic (D3h) isomer of carbon trioxide (12C16O3) via its ,1 and ,2 vibrational modes centered around 1165 cm,1 under matrix isolation conditions; the identification of the 12C18O3, 13C16O3, 13C18O3, 16O12C18O2, and 18O12C16O2 isotopomers of the acyclic isomer confirms the assignments. [source]

Atmospheric chemistry of isopropyl formate and tert -butyl formate

Andre Silva Pimentel
Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH3)2, and tert -butyl formate, HC(O)OC(CH3)3. Product distributions are reported from both Cl- and OH-initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the ,-ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15,20%). The OH radical initiated oxidation of tert -butyl formate gives acetone, formaldehyde, and CO2 as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10,12, and with Cl (1.75 ± 0.35) × 10,11, and for tert -butyl formate with Cl (1.45 ± 0.30) × 10,11 cm3 molecule,1 s,1. Simple group additivity rules fail to explain the observed distribution of sites of H-atom abstraction for simple formates. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 479,498, 2010 [source]

Mass-independent fractionation of sulfur isotopes in sulfides from the pre-3770 Ma Isua Supracrustal Belt, West Greenland

GEOBIOLOGY, Issue 4 2006
ABSTRACT Redox chemistry of the coupled atmosphere,hydrosphere system has coevolved with the biosphere, from global anoxia in the Archean to an oxygenated Proterozoic surface environment. However, to trace these changes to the very beginning of the rock record presents special challenges. All known Eoarchean (c. 3850,3600 Ma) volcanosedimentary successions (i.e. supracrustal rocks) are restricted to high-grade gneissic terranes that seldom preserve original sedimentary structures and lack primary organic biomarkers. Although complicated by metamorphic overprinting, sulfur isotopes from Archean supracrustal rocks have the potential to preserve signatures of both atmospheric chemistry and metabolic fractionation from the original sediments. We present a synthesis of multiple sulfur isotope measurements (32S, 33S and 34S) performed on sulfides from amphibolite facies banded iron-formations (BIFs) and ferruginous garnet-biotite (metapelitic) schists from the pre-3770 Ma Isua Supracrustal Belt (ISB) in West Greenland. Because these data come from some of the oldest rocks of interpretable marine sedimentary origin, they provide the opportunity to (i) explore for possible biosignatures of sulfur metabolisms in early life; (ii) assess changes in atmospheric redox chemistry from ,3.8 Ga; and (iii) lay the groundwork to elucidate sulfur biogeochemical cycles on the early Earth. We find that sulfur isotope results from Isua do not unambiguously indicate microbially induced sulfur isotopic fractionation at that time. A significantly expanded data set of ,33S analyses for Isua dictates that the atmosphere was devoid of free oxygen at time of deposition and also shows that the effects of post-depositional metamorphic remobilization and/or dilution can be traced in mass-independently fractionated sulfur isotopes. [source]

Biogeochemical modelling of the rise in atmospheric oxygen

GEOBIOLOGY, Issue 4 2006
ABSTRACT Understanding the evolution of atmospheric molecular oxygen levels is a fundamental unsolved problem in Earth's history. We develop a quantitative biogeochemical model that simulates the Palaeoproterozoic transition of the Earth's atmosphere from a weakly reducing state to an O2 -rich state. The purpose is to gain an insight into factors that plausibly control the timing and rapidity of the oxic transition. The model uses a simplified atmospheric chemistry (parameterized from complex photochemical models) and evolving redox fluxes in the Earth system. We consider time-dependent fluxes that include organic carbon burial and associated oxygen production, reducing gases from metamorphic and volcanic sources, oxidative weathering, and the escape of hydrogen to space. We find that the oxic transition occurs in a geologically short time when the O2 -consuming flux of reducing gases falls below the flux of organic carbon burial that produces O2. A short timescale for the oxic transition is enhanced by a positive feedback due to decreasing destruction of O2 as stratospheric ozone forms, which is captured in our atmospheric chemistry parameterization. We show that one numerically self-consistent solution for the rise of O2 involves a decline in flux of reducing gases driven by irreversible secular oxidation of the crust caused by time-integrated hydrogen escape to space in the preoxic atmosphere, and that this is compatible with constraints from the geological record. In this model, the timing of the oxic transition is strongly affected by buffers of reduced materials, particularly iron, in the continental crust. An alternative version of the model, where greater fluxes of reduced hydrothermal cations from the Archean seafloor consume O2, produces a similar history of O2 and CH4. When climate and biosphere feedbacks are included in our model of the oxic transition, we find that multiple ,Snowball Earth' events are simulated under certain circumstances, as methane collapses and rises repeatedly before reaching a new steady-state. [source]

Monoterpene emissions from rubber trees (Hevea brasiliensis) in a changing landscape and climate: chemical speciation and environmental control

Abstract Emissions of biogenic volatile organic compounds (VOCs) have important roles in ecophysiology and atmospheric chemistry at a wide range of spatial and temporal scales. Tropical regions are a major global source of VOC emissions and magnitude and chemical speciation of VOC emissions are highly plant-species specific. Therefore it is important to study emissions from dominant species in tropical regions undergoing large-scale land-use change, for example, rubber plantations in South East Asia. Rubber trees (Hevea brasiliensis) are strong emitters of light-dependent monoterpenes. Measurements of emissions from leaves were made in the dry season in February 2003 and at the beginning of the wet season in May 2005. Major emitted compounds were sabinene, , -pinene and , -pinene, but , -ocimene and linalool also contributed significantly at low temperature and light. Cis -ocimene was emitted with a circadian course independent of photosynthetic active radiation (PAR) and temperature changes with a maximum in the middle of the day. Total isoprenoid VOC emission potential at the beginning of the wet season (94 ,g gdw,1 h,1) was almost two orders of magnitude higher than measured in the dry season (2 ,g g dw,1 h,1). Composition of total emissions changed with increasing temperature or PAR ramps imposed throughout a day. As well as light and temperature, there was evidence that assimilation rate was also a factor contributing to seasonal regulating emission potential of monoterpenes from rubber trees. Results presented here contribute to a better understanding of an important source of biogenic VOC associated with land-use change in tropical South East Asia. [source]

Thermochemistry for enthalpies and reaction paths of nitrous acid isomers

Rubik Asatryan
Recent studies show that nitrous acid, HONO, a significant precursor of the hydroxyl radical in the atmosphere, is formed during the photolysis of nitrogen dioxide in soils. The term nitrous acid is largely used interchangeably in the atmospheric literature, and the analytical methods employed do not often distinguish between the HONO structure (nitrous acid) and HNO2 (nitryl hydride or isonitrous acid). The objective of this study is to determine the thermochemistry of the HNO2 isomer, which has not been determined experimentally, and to evaluate its thermal and atmospheric stability relative to HONO. The thermochemistry of these isomers is also needed for reference and internal consistency in the calculation of larger nitrite and nitryl systems. We review, evaluate, and compare the thermochemical properties of several small nitric oxide and hydrogen nitrogen oxide molecules. The enthalpies of HONO and HNO2 are calculated using computational chemistry with the following methods of analysis for the atomization, isomerization, and work reactions using closed- and open-shell reference molecules. Three high-level composite methods G3, CBS-QB3, and CBS-APNO are used for the computation of enthalpy. The enthalpy of formation, ,Hof(298 K), for HONO is determined as ,18.90 ± 0.05 kcal mol,1 (,79.08 ± 0.2 kJ mol,1) and as ,10.90 ± 0.05 kcal mol,1 (,45.61 ± 0.2 kJ mol,1) for nitryl hydride (HNO2), which is significantly higher than values used in recent NOx combustion mechanisms. H-NO2 is the weakest bond in isonitrous acid; but HNO2 will isomerize to HONO with a similar barrier to the HONO bond energy; thus, it also serves as a source of OH in atmospheric chemistry. Kinetics of the isomerization is determined; a potential energy diagram of H/N/O2 system is presented, and an analysis of the triplet surface is initiated. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 378,398, 2007 [source]

Isomeric hexyl-ketohydroperoxides formed by reactions of hexoxy and hexylperoxy radicals in oxygen

François Jorand
Isomerization reactions of peroxy radicals during oxidation of long-chain hydrocarbons yield hydroperoxides, and therefore play an important role in combustion and atmospheric chemistry, because of their action as branching agents in these chain reaction processes. Different formation mechanisms and structures are involved. Three isomeric hexyl-ketohydroperoxides are formed via isomerization reactions in oxygen of either hexoxy RO or hexylperoxy RO2 radicals. In the temperature range 373,473 K, 2-hexoxy (C6H13O) radical in O2/N2 mixtures gives 2-hexanone-5-hydroperoxide via two consecutive isomerizations. The second one is a H transfer from a HC(OH) group occurring via a seven-membered ring intermediate: Its rate constant has been determined at 453 and 483 K, and the general expression can be written as Hexylperoxy C6H13O2 radical, present in n -hexane oxidation by oxygen/nitrogen mixtures in the temperature range 543,573 K, gives 2-hexanone-4-hydroperoxide, 3-hexanone-5-hydroperoxide, and 2-hexanone-5-hydroperoxide. The first two are formed through an isomerization reaction via a six-membered ring intermediate, and the last through an isomerization reaction via a seven-membered ring intermediate. The ratio of the rate constant of the isomerization reactions of RO2 radicals via a seven-membered ring intermediate to that via a six-membered ring is found to be 0.795, and the rate constant expression via a seven-membered ring intermediate is proposed: The role of these reactions in the formation of radicals in the troposphere is discussed. Other products arising in the reactional path, such as ketones, furans, and diketones, are identified. Identification of these ketohydroperoxides was made using gas chromatography/mass spectrometry with electron impact, and with NH3 (or ND3) chemical ionization. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 354,366, 2003 [source]

From molecules to meteorology via turbulent scale invariance

A. F. Tuck
Abstract This review attempts to interpret the generalized scale invariance observed in common atmospheric variables,wind, temperature, humidity, ozone and some trace species,in terms of the computed emergence of ring currents (vortices) in simulations of populations of Maxwellian molecules subject to an anisotropy in the form of a flux. The data are taken from ,horizontal' tracks of research aircraft and from ,vertical' trajectories of research dropsondes. It is argued that any attempt to represent the energy distribution in the atmosphere quantitatively must have a proper basis in molecular physics, a prerequisite to accommodate the observed long-tailed velocity probability distributions and the implied effects on radiative transfer, atmospheric chemistry, turbulent structure and the definition of temperature itself. The relationship between fluctuations and dissipation is discussed in a framework of non-equilibrium statistical mechanics, and a link between maximization of entropy production and scale invariance is hypothesized. Copyright © 2010 Royal Meteorological Society [source]

Opportunities for enhanced collaboration within the data assimilation community

Dennis McLaughlin
Abstract Recent advances in sensor technology, telecommunications and computation open up new possibilities for the application of data assimilation concepts across the Earth sciences. As a result, the data assimilation community is expanding beyond meteorology and oceanography to include representatives from climatology, hydrology, atmospheric chemistry, ecology and other disciplines. This development offers new opportunities for collaboration between the operational and research sides of the community. Opportunities exist not only in traditional forecasting applications, but also in areas such as reanalysis, model diagnosis, development of new model parametrizations, and observing-system design. Disciplinary scientists from outside the traditional data assimilation community are starting to appreciate that data assimilation can provide an integrated view of earth processes over a range of time and space scales. Operational data assimilation groups have special expertise and capabilities that are needed by newcomers to the field. If the scope of the operational community expands to include a wider range of applications, the entire field will likely benefit from new ideas, new resources, and increased visibility and recognition. Copyright © 2005 Royal Meteorological Society [source]

Convective mixing in a tropopause fold

H. J. Reid
Abstract We present a case study of the passage of a tropopause fold over the UK behind a cold front, with emphasis on the mixing caused by convection extending into the fold. The event took place on 15,16 January 1999, and was the subject of intensive observations using the Met Office C130 aircraft and the mesosphere,stratosphere,troposphere (MST) radar at Aberystwyth. Here we concentrate on radar and satellite observations during the afternoon of 16 January, when the surface cold front had passed over the UK. A tongue of moist air moved north-eastwards over Wales at 700 hPa at this time, which, because of the very dry air in the fold above, resulted in potential instability. The resulting convection was clearly observed in NOAA satellite images. The MST radar depicted the passage of the cold front and tropopause fold as a layer of high-echo power and vertical wind shear ascending with time. Spectral widths showed the fold to be free of turbulence until 1200 UTC on 16 January, when convection was observed reaching into the frontal zone and generating turbulence. Eddy dissipation and diffusivity rates of 8.6 mW kg,1 and 8.5 m2s,1, respectively, were derived for this event. To place these figures in context, they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar, each resulting from shear rather than convective instability. The convective event is found to be comparable to the strongest shear events, and to correspond to moderate turbulence as experienced by an aircraft. This process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1,2 hours. Copyright © 2004 Royal Meteorological Society [source]

A review on the use of the adjoint method in four-dimensional atmospheric-chemistry data assimilation

K.-Y. Wang
Abstract In this paper we review a theoretical formulation of the adjoint method to be used in four-dimensional (4D) chemistry data assimilation. The goal of the chemistry data assimilation is to combine an atmospheric-chemistry model and actual observations to produce the best estimate of the chemistry of the atmosphere. The observational dataset collected during the past decades is an unprecedented expansion of our knowledge of the atmosphere. The exploitation of these data is the best way to advance our understanding of atmospheric chemistry, and to develop chemistry models for chemistry-climate prediction. The assimilation focuses on estimating the state of the chemistry in a chemically and dynamically consistent manner (if the model allows online interactions between chemistry and dynamics). In so doing, we can: produce simultaneous and chemically consistent estimates of all species (including model parameters), observed and unobserved; fill in data voids; test the photochemical theories used in the chemistry models. In this paper, the Hilbert space is first formulated from the geometric structure of the Banach space, followed by the development of the adjoint operator in Hilbert space. The principle of the adjoint method is described, followed by two examples which show the relationship of the gradient of the cost function with respect to the output vector and the gradient of the cost function with respect to the input vector. Applications to chemistry data assimilation are presented for both continuous and discrete cases. The 4D data variational adjoint method is then tested in the assimilation of stratospheric chemistry using a simple catalytic ozone-destruction mechanism, and the test results indicate that the performance of the assimilation method is good. [source]

Health monitoring of plants by their emitted volatiles: trichome damage and cell membrane damage are detectable at greenhouse scale

R.M.C. Jansen
Abstract Pathogen attack and herbivore infestation have a major impact on plant health. In a model study, these two plant health issues were simulated to study whether plant health can be monitored at greenhouse scale through the analysis of volatile organic compounds (VOCs) in greenhouse atmosphere. To simulate pathogen attack and herbivore infestation, we repeatedly stroked the stems of tomato plants (Lycopersicon esculentum) and repeatedly removed their side shoots. In addition, we studied the effect of fruit picking on the concentration of plant-emitted VOCs in greenhouse atmosphere. Analysis of air samples obtained before these treatments revealed up to 17 VOCs that are known to be released from tomato plants, of which the most dominant one was the monoterpene ,-phellandrene. When plants were 7 weeks old, the concentration of this VOC was approximately 0.06 ppbv before treatment. When plants were 12 weeks old, this concentration was raised to approximately 0.14 ppbv. Stroking of the stems, removing the side shoots and fruit picking resulted in an increase in the concentrations of all mono- and most sesquiterpenes up to 60-fold, which was expected because these VOCs are well-known constituents of trichomes. The treatments did not result in substantially increased concentrations of the stress-related compounds ,-copaene, methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene. In contrast to stroking and fruit picking, shoot removal resulted in the emission of the lipoxygenase-derived product (Z)-3-hexenol in greenhouse atmosphere expressing cell membrane degradation. The findings presented in this paper focus on the feasibility of monitoring plant health through the analysis of VOCs in greenhouse air, but findings might also be relevant for atmospheric chemistry. [source]

Transportprozesse in der Atmosphäre

Martin Schultz Dr.
Transportvorgänge in der Atmosphäre bestimmen, wie Spurenstoffe verteilt werden und wohin sich Schadstoffwolken ausbreiten. In diesem Aufsatz werden einige Grundlagen zu atmosphärischen Transportvorgängen erörtert und die Zusammenhänge zwischen Luftchemie und Winden aufgezeigt. Anhand einiger Beispiele aus der aktuellen Forschung wird verdeutlicht, welche Bedeutung Transportprozesse auf der lokalen bis interkontinentalen Skala für die Belastung der Luft mit Schadstoffen haben können. Atmospheric transport determines how trace substances and air pollutants are dispersed from their source regions. This article describes various transport processes and their interaction with atmospheric chemistry. Using a number of examples from current research the relevance of atmospheric transport from the local to the intercontinental scale on air quality is shown. [source]