Abundances and variability of tropospheric volatile organic compounds at the South Pole and other Antarctic locations

Multiyear (2000-2006) seasonal measurements of carbon monoxide, hydrocarbons, halogenated species, dimethyl sulfide, carbonyl sulfide and C1-C4 alkyl nitrates at the South Pole are presented for the first time. At the South Pole, short-lived species (such as the alkenes) typically were not observed above their limits of detection because of long transit times from source regions. Peak mixing ratios of the longer lived species with anthropogenic sources were measured in late winter (August and September) with decreasing mixing ratios throughout the spring. In comparison, compounds with a strong oceanic source, such as bromoform and methyl iodide, had peak mixing ratios earlier in the winter (June and July) because of decreased oceanic production during the winter months. Dimethyl sulfide (DMS), which is also oceanically emitted but has a short lifetime, was rarely measured above 5 pptv. This is in contrast to high DMS mixing ratios at coastal locations and shows the importance of photochemical removal during transport to the pole. Alkyl nitrate mixing ratios peaked during April and then decreased throughout the winter. The dominant source of the alkyl nitrates in the region is believed to be oceanic emissions rather than photochemical production due to low alkane levels.Sampling of other tropospheric environments via a Twin Otter aircraft included the west coast of the Ross Sea and large stretches of the Antarctic Plateau. In the coastal atmosphere, a vertical gradient was found with the highest mixing ratios of marine emitted compounds at low altitudes. Conversely, for anthropogenically produced species the highest mixing ratios were measured at the highest altitudes, suggesting long-range transport to the continent. Flights flown through the plume of Mount Erebus, an active volcano, revealed that both carbon monoxide and carbonyl sulfide are emitted with an OCS/CO molar ratio of 3.3 × 10-3 consistent with direct observations by other investigators within the crater rim. © 2010

Power-dependent speciation of volatile organic compounds in aircraft exhaust

As part of the third NASA Aircraft Particle Emissions Experiment (APEX-3, November 2005), whole air samples were collected to determine the emission rates of volatile organic compounds (VOCs) from aircraft equipped with three different gas-turbine engines (an Allison Engine 3007-A1E, a Pratt-Whitney 4158, and a Rolls-Royce RB211-535E4B). Samples were collected 1 m behind the engine exhaust plane of the engines while they were operated at powers ranging from idle up to 30% of maximum rated thrust.Exhaust emission indices (mass emitted per kilogram of fuel used) for CO and non-methane hydrocarbons (NMHCs) were calculated based on enhancements over background relative to CO 2. Emissions of all NMHCs were greatest at low power with values decreasing by an order of magnitude with increasing power. Previous studies have shown that scaling idle hydrocarbon emissions to formaldehyde or ethene (which are typically emitted at a ratio of 1-to-1 at idle) reduces variability amongst engine types. NMHC emissions were found to scale at low power, with alkenes contributing over 50% of measured NMHCs. However, as the power increases hydrocarbon emissions no longer scale to ethene, as the aromatics become the dominant species emitted. This may be due in part to a shift in combustion processes from thermal cracking (producing predominantly alkenes) to production of new molecules (producing proportionally more aromatics) as power increases. The formation of these aromatics is an intermediate step in the production of soot, which also increases with increasing power. The increase in aromatics relative to alkenes additionally results in a decrease in the hydroxyl radical reactivity and ozone formation potential of aircraft exhaust.Samples collected 30 m downwind of the engine were also analyzed for NMHCs and carbonyl compounds (acetone, 2-butanone and C 1-C 9 aldehydes). Formaldehyde was the predominant carbonyl emitted; however, the ratio of ethene-to-formaldehyde varied between the aircraft, possibly due to the sampling of transient emissions such as engine start-up and power changes. A large portion of the measured emissions (27-42% by mass) in the plume samples was made up of hazardous air pollutants (HAPs) with oxygenated compounds being most significant. © 2012

Measurements of nonmethane hydrocarbons in 28 United States cities

Between 1999 and 2005 a sampling campaign was conducted to identify and quantify the major species of atmospheric nonmethane hydrocarbons (NMHCs) in United States cities. Whole air canister samples were collected in 28 cities and analyzed for methane, carbon monoxide (CO) and NMHCs. Ambient mixing ratios exhibited high inter- and intra-city variability, often having standard deviations in excess of 50% of the mean value. For this reason, ratios of individual NMHC to CO, a combustion tracer, were examined to facilitate comparison between cities. Ratios were taken from correlation plots between the species of interest and CO, and most NMHCs were found to have correlation coefficients (r2) greater than 0.6, particularly ethene, ethyne and benzene, highlighting the influence of vehicular emissions on NMHC mixing ratios. Notable exceptions were the short-chain alkanes, which generally had poor correlations with CO. Ratios of NMHC vs. CO were also used to identify those cities with unique NMHC sources. © 2007 Elsevier Ltd. All rights reserved

High Resolution Polar Kerr Effect Measurements of Sr2RuO4: Evidence for Broken Time Reversal Symmetry in the Superconducting State

Polar Kerr effect in the spin-triplet superconductor Sr2RuO4 was measured with high precision using a Sagnac interferometer with a zero-area Sagnac loop. We observed non-zero Kerr rotations as big as 65 nanorad appearing below Tc in large domains. Our results imply a broken time reversal symmetry state in the superconducting state of Sr2RuO4, similar to He3-A

Pathophysiological Implications of Different Bicuspid Aortic Valve Configurations

There are numerous types of bicuspid aortic valve (BAV) configurations. Recent findings suggest that various BAV types represent different pathophysiological substrates on the aortic media level. Data imply that the BAV type is probably not related to location and extent of the aneurysm. However, BAV type is likely linked to the severity of aortic media disease. Some BAVs with raphe seem more aggressive than BAV without a raphe. Cusp fusion pattern, altered hemodynamics, and the qualitative severity of the disease in the aortic media might on the one hand share the same substrate. On the other hand, the aortopathy's longitudinal extent and location may represent a different pathophysiological substrate, probably dictated by the heritable aspects of BAV disease. The exact nature of the relation between BAV type and the aneurysm's location and extent as well as to the risk of aortic complications remains unclear. This paper reviews results of recent human and experimental studies on the significance of BAV types for local aortic media disease and location and extent of the aortopathy. We describe the known and hypothesized hemodynamic and hereditary factors that may result in aortic aneurysm formation in BAV patients

Development of a frequency-detuned interferometer as a prototype experiment for next-generation gravitational-wave detectors

We report on our prototype experiment that uses a 4-m detuned resonant sideband extraction interferometer with suspended mirrors, which has almost the same configuration as the next-generation, gravitational-wave detectors. We have developed a new control scheme and have succeeded in the operation of such an interferometer with suspended mirrors for the first time ever as far as we know. We believe that this is the first such instrument that can see the radiation pressure signal enhancement, which can improve the sensitivity of next-generation gravitational-wave detectors

Hydroxyl concentration estimates in the sunlit snowpack at Summit, Greenland

Experiments were performed at Summit, Greenland (72°34′ N, 38°29′ W) to investigate hydroxyl mixing ratios in the sunlit surface snowpack (or firn). We added a carefully selected mixture of hydrocarbon gases (with a wide range of hydroxyl reactivities) to a UV and visible light transparent flow chamber containing undisturbed natural firn. The relative decrease in mixing ratios of these gases allowed estimation of the lower limit mixing ratio of hydroxyl radicals in the near-surface firn pore spaces. Hydroxyl mixing ratios in the firn air followed a diurnal cycle in summer 2003 (10-12 July), with peak values of more than 3.2×106 molecules cm-3 between 13:00 and 16:00 local time. The minimum value estimated was 1.1×106 molecules cm-3 at 20:00 local time. Results during spring of 2004 showed lower, but rapidly increasing, peak hydroxyl mixing ratios of 1.1×106 molecules cm-3 in the early afternoon on 15 April and 1.5×106 molecules cm-3 on 1 May. Our firn hydroxyl estimates were similar to directly measured above-snow ambient levels during the spring field season, but were only about 30% of ambient levels during summer. © 2007 Elsevier Ltd. All rights reserved