2,355 research outputs found
Observations of total peroxy nitrates and aldehydes: measurement interpretation and inference of OH radical concentrations
We describe measurements of total peroxy nitrates (ΣPNs), NO<sub>2</sub>, O<sub>3</sub> and several aldehydes at Granite Bay, California, during the Chemistry and Transport of the Sacramento Urban Plume-2001 (CATSUP 2001) campaign, from 19 July–16 September 2001. We observed a strong photochemically driven variation of ΣPNs during the day with the median of 1.2 ppb at noon. Acetaldehyde, pentanal, hexanal and methacrolein had median abundances in the daytime of 1.2 ppb, 0.093 ppb, 0.14 ppb, and 0.27 ppb, respectively. We compare steady state and time dependent calculations of the dependence of ΣPNs on aldehydes, OH, NO and NO<sub>2</sub> showing that the steady state calculations are accurate to ±30% between 10:00 and 18:00 h. We use the steady state calculation to investigate the composition of ΣPNs and the concentration of OH at Granite Bay. We find that PN molecules that have never been observed before make up an unreasonably large fraction of the ΣPNs unless we assume that there exists a PAN source that is much larger than the acetaldehyde source. We calculate that OH at the site varied between 2 and 7×10<sup>6</sup> molecule cm<sup>−3</sup> at noon during the 8 weeks of the experiment
GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055
We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of
Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic
disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high
ionization absorption is strong, with line strengths consistent with the
spectral signature expected for hot (log T = 5-6) collisionally ionized gas in
either a ``Galactic fountain'' or an inhomogeneous medium containing a mixture
of conductive interfaces and turbulent mixing layers. The total O VI column
density of log N ~ 15 suggests that the scale height of O VI is large (>3 kpc)
in this direction. Comparison of the high ion column densities with
measurements for other sight lines indicates that the highly ionized gas
distribution is patchy. The amount of O VI perpendicular to the Galactic plane
varies by at least a factor of ~4 among the complete halo sight lines thus far
studied. In addition to the high ion absorption, lines of low ionization
species are also present in the spectra. With the possible exception of Ar I,
which may have a lower than expected abundance resulting from partial
photoionization of gas along the sight line, the absorption strengths are
typical of those expected for the warm, neutral interstellar medium. The sight
line intercepts a cold molecular cloud with log N(H2) ~ 19. The cloud has an
identifiable counterpart in IRAS 100-micron emission maps of this region of the
sky. We detect a Ly-alpha absorber associated with ESO141-055 at z = 0.03492.
This study presents an enticing glimpse into the interstellar and intergalactic
absorption patterns that will be observed at high spectral resolution by the
Far Ultraviolet Spectroscopic Explorer.Comment: 24 pages + 8 figures, uses aaspp4.sty. Accepted for publication in
Ap
The influence of coal particle and air jet momenta on MILD combustion in a recuperative furnace
The moderate or intense low-oxygen dilution (MILD) combustion regime is a promising technology that operates at high combustion efficiency and lessens pollutant emissions. This numerical study of a parallel jet recuperative MILD combustion furnace investigates the effects of coal particle size and inlet air momentum on furnace dynamics and global CO emissions. It is found that coal particle size affects the coal penetration depth within the furnace and the location of a particle stagnation point. The effects of air inlet momentum are tested in two ways, first by raising the inlet temperature at constant mass flow rate, and second by increasing the mass flow rate at constant temperature. In both cases, increasing the air jet momentum broadens the reaction zone and facilitates MILD combustion, but also increases CO emissions due to lowered reaction rates.Emmet M. Cleary, Paul R. Medwell, Bassam B. Dallyhttp://cfe.uwa.edu.au/news/acs2013http://www.anz-combustioninstitute.org
Observations of total peroxy nitrates and aldehydes: measurement interpretation and inference of OH radical concentrations
International audienceWe describe measurements of total peroxy nitrates (?PNs), NO2, O3 and several aldehydes at Granite Bay, California, during the Chemistry and Transport of the Sacramento Urban Plume-2001 (CATSUP 2001) campaign, from 19 July?16 September 2001. We observed a strong photochemically driven variation of ?PNs during the day with the median of 1.2 ppb at noon. Acetaldehyde, pentanal, hexanal and methacrolein had median abundances in the daytime of 1.2 ppb, 0.093 ppb, 0.14 ppb, and 0.27 ppb, respectively. We compare steady state and time dependent calculations of the dependence of ?PNs on aldehydes, OH, NO and NO2 showing that the steady state calculations are accurate to ±30% between 10:00 and 18:00 h. We use the steady state calculation to investigate the composition of ?PNs and the concentration of OH at Granite Bay. We find that PN molecules that have never been observed before make up an unreasonably large fraction of the ?PNs unless we assume that there exists a PAN source that is much larger than the acetaldehyde source. We calculate that OH at the site varied between 2 and 7×106 molecule cm?3 at noon during the 8 weeks of the experiment
Mixed-state quasiparticle transport in high-T_c cuprates: localization by magnetic field
Theory of quasiparticle transport in the mixed state of a d-wave
superconductor is developed under the assumption of disordered vortex array. A
novel universal regime is identified at fields above H*= c*H_{c2}(T/T_c)^2,
characterized by a field-independent longitudinal thermal conductivity. It is
argued that this behavior is responsible for the high-field plateau in the
thermal conductivity experimentally observed in cuprates by Krishana, Ong and
co-workers.Comment: 4 pages REVTeX + 1 PostScript figure. Final version to appear in PRL.
Several changes in response to referee comments. For related work and info
visit http://www.pha.jhu.edu/~fran
A study of combustion characteristics of pulverised coal under MILD combustion conditions
In this experimental work, a laboratory-scale recuperative furnace has been used to investigate the sustainability of Moderate or Intense Low Oxygen Dilution (MILD) combustion with pulverised coal. Low-rank and high volatile Kingston brown coal and high-rank and low volatile Bowen Basin black coal with particle size in the range of 38-180 ÎĽm were injected into the furnace using either CO2 or N2 as a carrier gas. Operating conditions for stable MILD combustion of pulverised coal have been identified and evidencing MILD condition is achievable without any additional pre-heating of the air. The O2 and CO emissions were measured in parallel with NO emission. A water cooled sampling probe was used to conduct in-furnace gas sampling. Measurements of in-furnace gas concentration of CO and NO and in-furnace temperatures are presented. It was found that a significant reduction of NO emission owing to the strong NO reburning reaction inside the furnace. These findings, together with the potentiality of MILD conditions for soot depression and destruction, open the possibility of using high rank black and low rank brown coal with this technology.M. Saha, B. B. Dally, P. R. Medwell and E. M. Clearyhttp://cfe.uwa.edu.au/news/acs2013http://www.anz-combustioninstitute.org
The weekend effect within and downwind of Sacramento ─ Part 1: Observations of ozone, nitrogen oxides, and VOC reactivity
Day-of-week patterns in human activities can be used to examine the ways in which differences in primary emissions result in changes in the rates of photochemical reactions, and the production of secondary pollutants. Data from twelve California Air Resources Board monitoring sites in Sacramento, CA, and the downwind Mountain Counties air basin are analyzed to reveal day of week patterns in ozone and its precursors in the summers of 1998–2002. Measurements of non-methane hydrocarbons are available for the summers of 2001–2003 at three of these sites and NO<sub>x</sub> at six of these sites for the full time period. This routine monitoring data is complemented by data sets of ozone and nitrogen oxide concentrations obtained in the summers of 2001 and 2003 at three sites in the region and comprehensive measurements of VOC reactivity at two sites in 2001. Daytime concentrations of nitrogen oxides (NO<sub>x</sub>≡NO+NO<sub>2</sub>) are approximately 35% lower on weekends at all the sites, whereas the VOC reactivity changes by less than 10%. All six sites in the Sacramento Valley have higher 8-h maximum average ozone on the weekend and are more likely to exceed the national standard of 85 ppb on the weekend. In contrast, all the sites in the Mountain Counties are less likely to exceed the federal ozone standard on the weekend. Analysis of the day-of-week trends in odd oxygen show that the weekend effect of ozone within Sacramento is strongly influenced by NO sources close to the monitoring sites. This suggests that ozone measurements from monitoring sites close to highways, including two rural locations, may not be representative of the regional abundance, and lead to underestimates of long term exposure for humans and ecosystems
The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
We present the final data release of observations of lambda 21-cm emission
from Galactic neutral hydrogen over the entire sky, merging the
Leiden/Dwingeloo Survey (LDS: Hartmann & Burton, 1997) of the sky north of
delta = -30 deg with the Instituto Argentino de Radioastronomia Survey (IAR:
Arnal et al., 2000, and Bajaja et al., 2005) of the sky south of delta = -25
deg. The angular resolution of the combined material is HPBW ~ 0.6 deg. The LSR
velocity coverage spans the interval -450 km/s to +400 km/s, at a resolution of
1.3 km/s. The data were corrected for stray radiation at the Institute for
Radioastronomy of the University of Bonn, refining the original correction
applied to the LDS. The rms brightness-temperature noise of the merged database
is 0.07 - 0.09 K. Residual errors in the profile wings due to defects in the
correction for stray radiation are for most of the data below a level of 20 -
40 mK. It would be necessary to construct a telescope with a main beam
efficiency of eta_{MB} > 99% to achieve the same accuracy. The merged and
refined material entering the LAB Survey of Galactic HI is intended to be a
general resource useful to a wide range of studies of the physical and
structural characteristices of the Galactic interstellar environment. The LAB
Survey is the most sensitive Milky Way HI survey to date, with the most
extensive coverage both spatially and kinematically.Comment: 9 pages, 5 figures, accepted for publication by Astronomy &
Astrophysic
Observations of total alkyl nitrates within the Sacramento Urban Plume
International audienceDuring the summer of 2001, NO2, total peroxy nitrates (?PNs), total alkyl nitrates (?ANs), HNO3, volatile organic compounds (VOC), CO2, O3, and meteorological variables were measured at Granite Bay, CA. The diurnal variation in ?PNs, ?ANs and HNO3 were all strongly correlated with sunlight, indicating both that they are photochemically produced and that they have a lifetime of a few hours at this site. The mixing ratios of ?ANs ranged as high as 2 ppbv. Mixing ratios at night averaged 0.4 ppbv. Odd-oxygen (Ox=O3+NO2) and ?ANs were strongly correlated reflecting both the common chemical source terms and the similar lifetimes of both species. Several approaches to interpreting the simultaneous variations of Ox and ?ANs are described, and used to derive a best estimate of the ?AN yield from the VOC mixture at this site of 4.2% and an estimate of the range that is consistent with the observations of 3.9?5.8%. A yield of 4.2% implies termination of the HOx catalytic cycle by ?AN formation once every 24 cycles. Analysis of the HNO3 observations in combination with the ?AN and O3 measurements suggests that NOx terminations limit the HOx chain length to between 4.7 and 6.3
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