On the estimation of overwater buoyancy length from routine measurements

The stability parameter (z/L, where z is the height and L the buoyancy length) is an essential parameter in atmospheric boundary layer studies. From routine measurements, the bulk Richardson number (R_b) is usually computed. On the basis of appropriate field measurements at sea, it is shown that z/L = A R_b where A = 10.2 (with R ² = 0.97) for unstable and 6.3 (with R ² = 0.97) for stable conditions, respectively. It is also demonstrated that the proposed simplified equations are in excellent agreement with those more complicated formulations.     

Air concentrations of polybrominated diphenyl ethers (PBDEs) in 2002–2004 at a rural site in the Great Lakes

Atmospheric PBDEs were measured on a monthly basis in 2002–2004 at Point Petre, a rural site in the Great Lakes. Average air concentrations were 7.0 ± 13 pg m^?3 for Σ₁₄BDE (excluding BDE-209), and 1.8 ± 1.5 pg m^?3 for BDE-209. Concentrations of 3 dominant congeners (i.e., BDE-47, 99, and 209) were comparable to previous measurements at remote/rural sites around the Great Lakes, but much lower than those at urban areas. Weak temperature dependence and strong linear correlations between relatively volatile congeners suggest importance of advective inputs of gaseous species. The significant correlation between BDE-209 and 183 implies their transport inputs associated with particles. Particle-bound percentages were found greater for highly brominated congeners than less brominated ones. These percentages increase with decreasing ambient temperatures. The observed gas/particle partitioning is consistent with laboratory measurements and fits well to the Junge–Pankow model. Using air mass back-trajectories, atmospheric transport to Point Petre was estimated as 76% for BDE-47, 67% for BDE-99, and 70% for BDE-209 from west–northwest and southwest directions. During the same time period, similar congener profiles and concentration levels were found at Alert in the Canadian High Arctic. Different inter-annual variations between Point Petre and Alert indicate that emissions from other regions than North America could also contribute PBDEs in the Arctic. In contrast to weak temperature effect at Point Petre, significant temperature dependence in the summertime implies volatilization emissions of PBDEs at Alert. Meanwhile, episodic observations in the wintertime were likely associated with enhanced inputs through long-range transport during the Arctic Haze period.     

Is natural hatching asynchrony optimal? An experimental investigation of sibling competition patterns in a facultatively siblicidal seabird

In unpredictable environments, any tactic that enables avian parents to adjust brood size and, thus, energy expenditure to environmental conditions should be favoured. Hatching asynchrony (HA), which occurs whenever incubation commences before clutch completion, may comprise such a tactic. For instance, the sibling rivalry hypothesis states that the hierarchy among chicks, concomitant to HA, should both facilitate the adjustment of brood size to environmental conditions and reduce several components of sibling competition as compared to synchronous hatching, at both brood and individual levels. We thus predicted that brood aggression, begging and feeding rates should decrease and that older chick superiority should increase with HA increasing, leading to higher growth and survival rates. Accordingly, we investigated the effects of an experimental upward and downward manipulation of HA magnitude on behaviour, growth and survival of black-legged kittiwake (Rissa tridactyla) chicks. In line with the sibling rivalry hypothesis, synchronous hatching increased aggression and tended to increase feeding rates by parents at the brood level. Begging rates, however, increased with HA contrary to our expectations. At the individual level, as HA magnitude increased, the younger chick was attacked and begged proportionally more often, experienced a slower growth and a higher mortality than its sibling. Overall, the occurrence of energetic costs triggered by synchronous hatching both for parents and chicks, together with the lower growth rate and increased mortality of the younger chick in highly asynchronous broods suggest that natural HA magnitude may be optimal.     

ESTIMATION OF SOIL MOISTURE FROM SEASAT SAR DATA1

ABSTRACT A study was made to determine if Seasat Synthetic Aperture Radar (SAR) data could be used to make practical estimates of soil moisture. Extensive ground measurements were collected at two primary sites near Guymon, Oklahoma, and Sublette, Kansas. The relative sensitivity of the SAR to differences in soil moisture, tillage roughness, and vegetation was determined. To validate the effects detected in the SAR data, an airborne scatterometer with a similar wavelength was flown repeatedly over the Guymon site. Soil moisture variations in the surface 2 cm and surface 15 cm of fields with bare soil, milo and alfalfa produce similar responses in the scattering coefficient from both systems. Roughness due to tillage in row crops produced as much as 12–15 dB increase in the scatterometer return. Most agricultural vegetation was effectively penetrated by the L-band frequencies; however, corn produced an exceptionally high radar return either standing or after combine harvesting. When corn had ripened, there was some evidence that tillage roughness could be detected through the canopy. Moderate tillage roughness produced by grain drill furrows caused over 12 dB increase in return when row directions changed from parallel to perpendicular with respect to the SAR look direction. Dramatic increases in return occurred when vegetation surfaces were wet. Increased radar returns from tillage roughness, some vegetation and wet vegetation surfaces, all dyanmic in nature, were significant and may limit the practical estimation of soil moisture from the radar data.     

Explosions in closed pipes containing baffles and 90 degree bends

There is a general lack of information on the effects of full-bore obstacles on combustion in the literature, these obstacles are prevalent in many applications and knowledge of their effects on phenomena including burning rate, flame acceleration and DDT is important for the correct placing of explosion safety devices such as flame arresters and venting devices. In this work methane, propane, ethylene and hydrogen–air explosions were investigated in an 18 m long DN150 closed pipe with a 90 degree bend and various baffle obstacles placed at a short distance from the ignition source. After carrying out multiple experiments with the same configuration it was found that a relatively large variance existed in the measured flame speeds and overpressures, this was attributed to a stochastic element in how flames evolved and also how they caused and interacted with turbulence to produce flame acceleration. This led to several experiments being carried out for one configuration in order to obtain a meaningful average. It was shown that a 90 degree bend in a long tube had the ability to enhance flame speeds and overpressures, and shorten the run-up distance to DDT to a varying degree for a number of gases. In terms of the qualitative effects on these parameters they were comparable to baffle type obstacles with a blockage ratios of between 10 and 20%.     

The Use of Ambient Measurements To Identify which Precursor Species Limit Aerosol Nitrate Formation

ABSTRACT

A thermodynamic equilibrium model was used to investigate the response of aerosol NO₃ to changes in concentrations of HNO₃, NH₃, and H₂SO₄. Over a range of temperatures and relative humidities (RHs), two parameters provided sufficient information for indicating the qualitative response of aerosol NO₃. The first was the excess of aerosol NH₄ ⁺ plus gas-phase NH₃ over the sum of HNO₃, particulate NO₃, and particulate SO₄ ^2- concentrations. The second was the ratio of particulate to total NO₃ concentrations. Computation of these quantities from ambient measurements provides a means to rapidly analyze large numbers of samples and identify cases in which inorganic aerosol NO₃ formation is limited by the availability of NH₃. Example calculations are presented using data from three field studies. The predictions of the indicator variables and the equilibrium model are compared.     

Weekday/Weekend differences in ambient air pollutant concentrations in atlanta and the southeastern United States

The authors quantified changes between mean weekday and weekend ambient concentrations of ozone (O3) precursors (volatile organic compounds [VOC], carbon monoxide [CO], nitric oxide, and oxides of nitrogen [NOx]) in Atlanta and surrounding areas to observe how weekend precursor emission levels influenced ambient O3 levels. The authors analyzed CO, nitric oxide (NO), and NO, measurements from 1998 to 2002 and speciated VOC from 1996 to 2003. They observed a strong weekend effect in the Atlanta region, with median daytime (6:00 a.m. to 3:00 p.m. Eastern Standard Time) decreases of 62%, 57%, and 31%, respectively, in the ambient levels of NO, NOx, and CO from Wednesdays to Sundays, during the ozone season (March to October). They also observed significant decreases in ambient VOC levels between Wednesdays and Sundays, with decreases of 28% for the sum of aromatic compounds and 19% for the sum of Photochemical Assessment Monitoring Stations target compounds. Despite large reductions in O3 precursor levels on weekends, day-of-week differences in O3 mixing ratios in and near Atlanta were much smaller. Averaging overall O3-season days, the 1-hr and 8-hr mean peak daily O3 maxima on Sundays were 4.5% and 2.3% lower, respectively, than their mean levels on Wednesdays (median of 14 site differences), with no sites showing statistically significant Wednesday-to-Sunday differences. When restricted to high-O3 days (highest 3 peak O3 days per day of week per site per year), the 1-hr and 8-hr Sunday O3 mixing ratios were 11% and 10% lower, respectively, than their mean peak levels on Wednesdays (median of 14 site differences), with 6 of 14 sites showing statistically significant Wednesday-to-Sunday differences. The analyses of weekday/weekend differences in O3 precursor concentrations show that different emission reductions than normally take place each weekend will be required to achieve major reductions in ambient ozone levels in the Atlanta area.     

Ecological consequences of forest elephant declines for Afrotropical forests

Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant‐free tropical forest. Elephants are ecological engineers that create and maintain forest habitat; thus, their loss will have large consequences for the composition and structure of Afrotropical forests. Through a comprehensive literature review, we evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of their population declines. Loss of seed dispersal by elephants will favor tree species dispersed abiotically and by smaller dispersal agents, and tree species composition will depend on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density with release from browsing pressures. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees and thus increase homogeneity of forest structure and decrease carbon stocks. The loss of ecological services by forest elephants likely means Central African forests will be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long‐term conservation will require land‐use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging.     

Recommended pre-test counseling points for noninvasive prenatal testing using cell-free DNA: a 2015 perspective

Noninvasive prenatal testing (NIPT) using cell-free DNA is being offered to an increasing number of women. Comprehensive pre-test counseling is complicated by emerging information about the benefits and limitations of testing, as well as the potential to detect incidental findings. Genetic counselors are trained to facilitate informed decision-making; however, not all centers have access to these professionals. To aid in the informed consent process, we have summarized key points to be included in discussions with patients who are considering NIPT. © 2015 John Wiley & Sons, Ltd.     

Quantitative Determination of Formaldehyde in the Parts Per Hundred Million Concentration Level

A new method has been developed for the determination of trace quantities of formaldehyde and appears to be superior to existing methods. The procedure is based on a modification of Schiff’s test for aldehydes. A mixture of dichlorosulfitomercurate II complex and acid bleached pararosaniline hydrochloride is used as the reagent. In the presence of formaldehyde, a purple color is produced. The method is highly sensitive to formaldehyde and acetaldehyde, simple and does not require concentrated acids. When applied to air pollution studies, the method is virtually free of interferences from higher aldehydes. The paper describes the application of this method to spot sampling of the atmosphere and to continuous atmospheric analysis.