504 research outputs found
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II ? gas phase reactions of organic species
International audienceThis article, the second in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of Organic species, which were last published in 1999, and were updated on the IUPAC website in late 2002, and subsequently during the preparation of this article. The article consists of a summary table of the recommended rate coefficients, containing the recommended kinetic parameters for the evaluated reactions, and eight appendices containing the data sheets, which provide information upon which the recommendations are made
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume III ? gas phase reactions of inorganic halogens
International audienceThis article, the third in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of inorganic halogen species, which were last published in J. Phys. Chem. Ref. Data, in 2000 (Atkinson et al., 2000), were updated on the IUPAC website in 2003 and are updated again in the present evaluation. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and five appendices containing the data sheets, which provide information upon which the recommendations were made
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species
This article, the second in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of Organic species, which were last published in 1999, and were updated on the IUPAC website in late 2002, and subsequently during the preparation of this article. The article consists of a summary table of the recommended rate coefficients, containing the recommended kinetic parameters for the evaluated reactions, and eight appendices containing the data sheets, which provide information upon which the recommendations are made
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume IV – gas phase reactions of organic halogen species
This article, the fourth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of organic halogen species, which were last published in 1997, and were updated on the IUPAC website in 2006/07. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and four appendices containing the data sheets, which provide information upon which the recommendations are made
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume V – heterogeneous reactions on solid substrates
This article, the fifth in the ACP journal series, presents data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the heterogeneous processes on surfaces of solid particles present in the atmosphere, for which uptake coefficients and adsorption parameters have been presented on the IUPAC website in 2010. The article consists of an introduction and guide to the evaluation, giving a unifying framework for parameterisation of atmospheric heterogeneous processes. We provide summary sheets containing the recommended uptake parameters for the evaluated processes. Four substantial appendices contain detailed data sheets for each process considered for ice, mineral dust, sulfuric acid hydrate and nitric acid hydrate surfaces, which provide information upon which the recommendations are made
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Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VII-Criegee intermediates
This article, the seventh in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers an extension of the gas-phase and photochemical reactions related to Criegee intermediates previously published in Atmospheric Chemistry and Physics (ACP) in 2006 and implemented on the IUPAC website up to 2020. The article consists of an introduction, description of laboratory measurements, a discussion of rate coefficients for reactions of O3 with alkenes producing Criegee intermediates, rate coefficients of unimolecular and bimolecular reactions and photochemical data for reactions of Criegee intermediates, and an overview of the atmospheric chemistry of Criegee intermediates. Summary tables of the recommended kinetic and mechanistic parameters for the evaluated reactions are provided. Data sheets summarizing information upon which the recommendations are based are given in two files, provided as a Supplement to this article. © Author(s) 2020
Shearing of loose granular materials: A statistical mesoscopic model
A two-dimensional lattice model for the formation and evolution of shear
bands in granular media is proposed. Each lattice site is assigned a random
variable which reflects the local density. At every time step, the strain is
localized along a single shear-band which is a spanning path on the lattice
chosen through an extremum condition. The dynamics consists of randomly
changing the `density' of the sites only along the shear band, and then
repeating the procedure of locating the extremal path and changing it. Starting
from an initially uncorrelated density field, it is found that this dynamics
leads to a slow compaction along with a non-trivial patterning of the system,
with high density regions forming which shelter long-lived low-density valleys.
Further, as a result of these large density fluctuations, the shear band which
was initially equally likely to be found anywhere on the lattice, gets
progressively trapped for longer and longer periods of time. This state is
however meta-stable, and the system continues to evolve slowly in a manner
reminiscent of glassy dynamics. Several quantities have been studied
numerically which support this picture and elucidate the unusual system-size
effects at play.Comment: 11 pages, 15 figures revtex, submitted to PRE, See also:
cond-mat/020921
The effect of photochemical ageing and initial precursor concentration on the composition and hygroscopic properties of β-caryophyllene secondary organic aerosol
The effect of photochemical ageing and initial precursor concentration on
the composition and hygroscopic properties of secondary organic aerosol
(SOA) formed during the chamber photo-oxidation of β-caryophyllene/NO<sub>x</sub>
mixtures were investigated. Nucleation of β-caryophyllene SOA particles occurred almost immediately after oxidation
was initiated and led to the formation of fresh SOA with a relatively
simpler composition than has been reported for monoterpenes. The SOA yield
values ranged from 9.5–26.7% and 30.4–44.5% using a
differential mobility particle sizer (DMPS) and an aerosol mass spectrometer
(AMS) mass based measurements, respectively. A total of 20 compounds were
identified in the SOA by LC-MS/MS, with the most abundant compounds
identified as β-caryophyllonic acid and β-caryophyllinic
acid/β-nocaryophyllonic acid. The O:C and H:C elemental ratios of
products identified in the condensed phase ranged from 0.20 to 1.00 and 1.00
to 2.00, with average values of 0.39 and 1.58, respectively. The increase in
the O:C ratio was associated with a decrease in the saturation concentration
of the identified compounds. The compounds identified in the lower initial
concentration experiments were more oxidised compared to those that were
found to be more abundant in the higher initial concentration experiments
with average O:C ratios of 0.51 and 0.27, respectively. Photochemical ageing
led to a more complex SOA composition with a larger contribution coming from
lower molar mass, higher generation products, where both double bonds had
been oxidised. This effect was more evident in the experiments conducted
using the lower initial precursor concentration; a finding confirmed by the
temporal behaviour of key organic mass fragment measured by an Aerosol Mass
Spectrometer. Although the composition changed with both initial precursor
concentration and ageing, this had no significant measurable effect on the
hygroscopic properties of the SOA formed. The latter finding might have been
influenced by the difference in pre-treatment of the semivolatile-containing
particles prior to their measurements
The formation, properties and impact of secondary organic aerosol: current and emerging issues
Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed
The nature and spatial variability of lowland savanna soils: Improving the resolution of soil properties to support land management policy
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