1,099 research outputs found
Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds
We report the first hourly in-situ measurements of speciated organic aerosol
(OA) composition in an urban environment. Field measurements were made in
southern California at the University of California–Riverside during the
2005 Study of Organic Aerosol at Riverside (SOAR), which included two
separate measurement periods: a summer study (15 July–15 August) and a
fall study (31 October–28 November). Hourly measurements of over 300
semivolatile and nonvolatile organic compounds were made using the thermal
desorption aerosol gas chromatograph (TAG). Positive matrix factorization
(PMF) was performed on a subset of these compounds to identify major
components contributing to submicron (i.e., PM<sub>1</sub>) OA at the site, as
measured by an aerosol mass spectrometer (AMS). PMF analysis was performed
on an 11-day focus period in each season, representing average seasonal
conditions during the summer and a period of urban influence during the
fall. As a result of this analysis, we identify multiple types of primary
and secondary OA (POA and SOA). Secondary sources contribute substantially
to fine OA mass at Riverside, which commonly receives regional air masses
that pass through metropolitan Los Angeles during the summer. Four
individual summertime SOA components are defined, and when combined, they
are estimated to contribute an average 88% of the total fine OA mass
during summer afternoons according to PMF results. These sources appear to
be mostly from the oxidation of anthropogenic precursor gases, with one SOA
component having contributions from oxygenated biogenics. During the fall,
three out of four aerosol components that contain SOA are inseparable from
covarying primary emissions, and therefore we cannot estimate the fraction
of total OA that is secondary in nature during the fall study. Identified
primary OA components are attributed to vehicle emissions, food cooking,
primary biogenics, and biomass burning aerosol. While a distinction between
local and regional vehicle emissions is made, a combination of these two
factors accounted for approximately 11% of observed submicron OA during
both sampling periods. Food cooking operations contributed ~10% of
submicron OA mass during the summer, but was not separable from SOA during
the fall due to high covariance of sources. Biomass burning aerosol
contributed a larger fraction of fine OA mass during the fall (~11%) than compared to summer (~7%). Primary biogenic aerosol
was also identified during the summer, contributing ~1% of the OA,
but not during the fall. While the contribution of both local and regional
primary vehicle OA accounts for only ~11% of total OA during both
seasons, gas-phase vehicle emissions likely create a substantial fraction of
the observed SOA as a result of atmospheric processing
Origins and composition of fine atmospheric carbonaceous aerosol in the Sierra Nevada Mountains, California
In this paper we report chemically resolved measurements
of organic aerosol (OA) and related tracers during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) at the Blodgett Forest Research Station, California from 15 August–10 October 2007. OA contributed the majority of the mass to the fine atmospheric particles and was predominately oxygenated (OOA). The highest concentrations of OA were during sporadic wildfire influence when aged plumes were impacting the site. In
situ measurements of particle phase molecular markers were dominated by secondary compounds and along with gas phase compounds could be categorized into six factors or sources: (1) aged biomass burning emissions and oxidized urban emissions, (2) oxidized urban emissions (3) oxidation products of monoterpene emissions, (4) monoterpene emissions, (5) anthropogenic emissions and (6) local
methyl chavicol emissions and oxidation products. There were multiple biogenic components that contributed to OA at this site whose contributions varied diurnally, seasonally and in response to changing meteorological conditions, e.g. temperature and precipitation events. Concentrations of isoprene oxidation products were larger when temperatures were higher during the first half of the campaign (15 August–12 September) due to more substantial emissions of isoprene and enhanced photochemistry. The oxidation of methyl chavicol, an oxygenated terpene emitted by
ponderosa pine trees, contributed similarly to OA throughout the campaign. In contrast, the abundances of monoterpene oxidation products in the particle phase were greater during the cooler conditions in the latter half of the campaign (13 September–10 October), even though emissions of the precursors were lower, although the mechanism is not known. OA was correlated with the anthropogenic tracers 2-propyl nitrate and carbon monoxide (CO), consistent with previous observations, while being comprised of mostly non-fossil carbon (>75%). The correlation between OA and an anthropogenic tracer does not necessarily identify the source of the carbon as being anthropogenic but instead suggests a coupling between the anthropogenic and biogenic components in the air mass that might be related to the source of the oxidant and/or the aerosol sulfate. Observations of organosulfates of isoprene and α-pinene provided evidence for the likely importance of aerosol sulfate in spite of neutralized aerosol although acidic plumes might have played a role upwind of the site. This is in contrast to laboratory studies where strongly acidic seed aerosols were needed in order to form these compounds. These compounds together represented only a minor fraction (<1%) of the total OA mass, which may be the result of the neutralized aerosol at the site or because only a small number of organosulfates were quantified. The low contribution of organosulfates to total OA suggests that other mechanisms, e.g. NO_x enhancement of oxidant levels, are likely responsible for the majority of the anthropogenic enhancement of biogenic secondary organic aerosol observed at this site
Disordered ultracold atomic gases in optical lattices: A case study of Fermi-Bose mixtures
We present a review of properties of ultracold atomic Fermi-Bose mixtures in
inhomogeneous and random optical lattices. In the strong interacting limit and
at very low temperatures, fermions form, together with bosons or bosonic holes,
{\it composite fermions}. Composite fermions behave as a spinless interacting
Fermi gas, and in the presence of local disorder they interact via random
couplings and feel effective random local potential. This opens a wide variety
of possibilities of realizing various kinds of ultracold quantum disordered
systems. In this paper we review these possibilities, discuss the accessible
quantum disordered phases, and methods for their detection. The discussed
quantum phases include Fermi glasses, quantum spin glasses, "dirty"
superfluids, disordered metallic phases, and phases involving quantum
percolation.Comment: 29 pages and 11 figure
Favorable outcome of early treatment of new onset child and adolescent migraine-implications for disease modification.
There is evidence that the prevalence of migraine in children and adolescents may be increasing. Current theories of migraine pathophysiology in adults suggest activation of central cortical and brainstem pathways in conjunction with the peripheral trigeminovascular system, which ultimately results in release of neuropeptides, facilitation of central pain pathways, neurogenic inflammation surrounding peripheral vessels, and vasodilatation. Although several risk factors for frequent episodic, chronic, and refractory migraine have been identified, the causes of migraine progression are not known. Migraine pathophysiology has not been fully evaluated in children. In this review, we will first discuss the evidence that early therapeutic interventions in the child or adolescent new onset migraineur, may halt or limit progression and disability. We will then review the evidence suggesting that many adults with chronic or refractory migraine developed their migraine as children or adolescents and may not have been treated adequately with migraine-specific therapy. Finally, we will show that early, appropriate and optimal treatment of migraine during childhood and adolescence may result in disease modification and prevent progression of this disease
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Speciated measurements of semivolatile and intermediate volatility organic compounds (S/IVOCs) in a pine forest during BEACHON-RoMBAS 2011
Understanding organic composition of gases and particles is essential to identifying sources and atmospheric processing leading to organic aerosols (OA), but atmospheric chemical complexity and the analytical techniques available often limit such analysis. Here we present speciated measurements of semivolatile and intermediate volatility organic compounds (S/IVOCs) using a novel dual-use instrument (SV-TAG-AMS) deployed at Manitou Forest, CO, during the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H_2O, Organics & Nitrogen – Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS) 2011 campaign. This instrument provides on-line speciation of ambient organic compounds with 2 h time resolution. The species in this volatility range are complex in composition, but their chemical identities reveal potential sources. Observed compounds of biogenic origin include sesquiterpenes with molecular formula C_(15)H_(24) (e.g., β-caryophyllene and longifolene), which were most abundant at night. A variety of other biogenic compounds were observed, including sesquiterpenoids with molecular formula C_(15)H_(22), abietatriene and other terpenoid compounds. Many of these compounds have been identified in essential oils and branch enclosure studies but were observed in ambient air for the first time in our study. Semivolatile polycyclic aromatic hydrocarbons (PAHs) and alkanes were observed with highest concentrations during the day and the dependence on temperature suggests the role of an evaporative source. Using statistical analysis by positive matrix factorization (PMF), we classify observed S/IVOCs by their likely sources and processes, and characterize them based on chemical composition. The total mass concentration of elutable S/IVOCs was estimated to be on the order of 0.7 µg m^(−3) and their volatility distributions are estimated for modeling aerosol formation chemistry
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Indoor, outdoor and regional profiles of PM2.5 sulfate, nitrateand carbon
Fine particle concentrations were measured simultaneously at three locations: a regional monitoring site in Fresno, California, a backyard of an unoccupied residence in Clovis, California located 6 km northeast of the regional site; and indoors at the same residence. Measurements included 10-min determination of PM{sub 2.5} nitrate, sulfate and carbon using an automated collection and vaporization system, and black carbon measured by light attenuation through a filter deposit. Specific outdoor PM{sub 2.5} constituents were compared to assess the appropriateness of using regional data to model indoor concentrations from outdoor sources. The outdoor data show that, in general, the regional results provide a good representation of the concentrations seen at the building exterior. The indoor concentrations showed considerable attenuation as well as a broadening and time-lag for the concentration peaks. The concentration reduction was the largest for PM{sub 2.5} nitrate, which appears to undergo phase changes in addition to indoor deposition and penetration losses
Point defects and clustering in uranium dioxide by LSDA+U calculations
A comprehensive investigation on point defects and their clustering behavior
in nonstoichiometric uranium dioxide UO2+x is carried out using LSDA+U method
based on density functional theory. Accurate energetic information and charge
transfers available so far are obtained. With these energies that have improved
more than 50% over that of pure GGA and LDA, we show the density functional
theory predicts the predominance of oxygen defects over uranium ones at any
compositions, which is possible only after treated the localized 5f electrons
properly. Calculations also suggest an upper bound of x~0.03 for oxygen
clusters to start off. The volume change induced by point uranium defects is
monotonic but nonlinear, whereas for oxygen defects, increase x always reduces
the system volume linearly, except dimers that require extra space for
accommodation, which has been identified as meta-stable ionic molecule. Though
oxygen dimers usually occupy Willis O'' sites and mimic a single oxygen in
energetics and charge state, they are rare at ambient conditions. Its
decomposition process and vibrational properties have been studied carefully.
To obtain a general clustering mechanism in anion-excess fluorites
systematically, we also analyze the local stabilities of possible basic
clustering modes of oxygen defects. The result shows an unified way to
understand the structure of Willis type and cuboctahedral clusters in UO2+x and
beta-U4O9. Finally we generalize the point defect model to the independent
clusters approximation to include clustering effects, the impact on defect
populations is discussed.Comment: 20 pages, 12 figure
Azimuthal dependence of pion source radii in Pb+Au collisions at 158 A GeV
We present results of a two-pion correlation analysis performed with the
Au+Pb collision data collected by the upgraded CERES experiment in the fall of
2000. The analysis was done in bins of the reaction centrality and the pion
azimuthal emission angle with respect to the reaction plane. The pion source,
deduced from the data, is slightly elongated in the direction perpendicular to
the reaction plane, similarly as was observed at the AGS and at RHIC.Comment: 5 pages, 2 figure
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