Modelled and measured concentrations of peroxy radicals and nitrate radical in the U.S. Gulf Coast region during TexAQS 2006

Measurements of total peroxy radicals (HO₂?+?RO₂) and nitrate radical (NO₃) were made on the NOAA research vessel R/V?Brown along the U.S. Gulf Coast during the TexAQS 2006 field campaign. The measurements were modelled using a constrained box-model based upon the Master Chemical Mechanism (MCM). The agreement between modelled and measured HO₂?+?RO₂ was typically within ??40% and, in the unpolluted regions, within 30%. The analysis of the model results suggests that the MCM might underestimate the concentrations of some acyl peroxy radicals and other small peroxy radicals. The model underestimated the measurements of NO₃ by 60?C70%, possibly because of rapid heterogeneous uptake of N₂O₅. The MCM model results were used to estimate the composition of the peroxy radical pool and to quantify the role of DMS, isoprene and alkenes in the formation of RO₂ in the different regions. The measurements of HO₂?+?RO₂ and NO₃ were also used to calculate the gas-phase budget of NO₃ and quantify the importance of organic peroxy radicals as NO₃ sinks. RO₂ accounted, on average, for 12?C28% of the total gas-phase NO₃ losses in the unpolluted regions and for 1?C2% of the total gas-phase NO₃ losses in the polluted regions.     

Short communications a modified design for lake-seston traps and a simple method for relocating them

A modified design of seston trap is described which has been used in Brotherswater, U.K. (Ordnance Survey NY 40 12). The trap was designed to collect larger quantities of seston than were found to collect in conventional types of seston trap. A simple concealed trap-location device is also described.     

Tangential discontinuities and the optical analogy for stationary fields. VII. Effects of resistivity

Abstract

The relatively large resistivity in the solar photosphere and chromosphere softens the ideal tangential discontinuities of magnetostatic equilibrium into continuous transitions in field direction over scales of 0.1–10 km. This softening is communicated upward at the Alfvén speed into the active solar corona. The degree of softening is a vital part of the theory of magnetic heat input to the active X-ray corona, because the very low resistivity of the coronal gas provides effective dissipation only if the current sheets are reduced to a thickness of 10^?2km.

A close examination of the problem shows that the Alfvén transit time up into the corona is large compared to the characteristic time of 1 sec in which the coronal tangential discontinutities are formed. It also shows that the principal effect of the resistivity is to create a thin surface layer of fluid on adjacent flux bundles, which causes a general drift of the flux but does not directly broaden the current sheets higher up in the field. In fact the motions of the surface layers do not extend upwards beyond the first winding pattern at each end of a coronal loop.

It appears that the photospheric and chromospheric resistivity is without striking consequences for magnetic heating in the corona.     

Comparison of Fiberglass and Other Polymeric Well Casings Part II. Sorption and Leaching of Trace-Level Organics

This paper contains the results of a laboratory study that was designed to compare sorption of low (mg/L) concentrations of 11 organic solutes by six polymeric materials (acrylonitrile butadiene styrene [ABS], fluorinated ethylene propylene [FEP], fiberglass-reinforced epoxy [FRE] and fiberglass-reinforced plastic [FRP], polyvinyl chloride [PVC], and poly-tetrafluoroethylene [PTFE]).
During this six-week study, ABS sorbed analytes much more rapidly and to a greater extent than did the other materials, and PVC and FRE sorbed analytes more slowly and to a lesser extent than the other materials tested.
As the study progressed, an increasing number of spurious peaks were found in the high performance liquid chromatography (HPLC) chromatograms of some of our samples, indicating that leaching of some consituents had occurred. By the end of the study, there were 11 additional peaks in the ABS samples, five in the FRP samples, and one in the FRE samples. Analysis by purge and trap gas chromatography/mass spectrometry (GC/MS) of those samples and of well water samples that were exposed to the casings for 500 hours revealed the identity of some of the leached constituents; acrylonitrile and styrene (components of ABS), chloroform and ethylbenzene (an intermediate in the production of styrene) from the ABS pipe, and toluene, 1,1,1-trichloroethane, and ethylbenzene from the FRP casing.     

Identification of Burrowing Shrimp Food Sources Along an Estuarine Gradient Using Fatty Acid Analysis and Stable Isotope Ratios

Two species of burrowing shrimp occur in high densities in US West Coast estuaries, the ghost shrimp, Neotrypaea californiensis, and the blue mud shrimp, Upogebia pugettensis. Both species of shrimp are considered ecosystem engineers as they bioturbate and irrigate extensive galleries within the sediment. While their burrows comprise a dominant habitat type in west coast estuaries, little is known about these shrimps’ diet and their role in estuarine food webs. The primary goals of this study were to identify major components of burrowing shrimp diets and detect variation in these diets along an estuarine gradient using combined fatty acid (FA) and stable isotope (SI) analyses. Shrimp and potential food sources including eelgrass blades, epiphytes, Ulva, sedimentary particulate organic matter (SPOM), burrow walls, and particulate organic material (POM) were sampled at different locations within Yaquina Bay, Oregon in August 2012. Both SI and FA analyses indicated differences in food resources assimilated by shrimp along the estuarine gradient. SI values showed that diets for U. pugettensis consisted of carbon sources derived primarily from POM and SPOM, while POM and epiphytes were primary carbon sources for N. californiensis. Shrimp from lower estuarine sites had high levels of 16:1ω7 and 20:5ω3 FAs suggesting their diet is enriched with marine diatoms. Shrimp from upriver showed greater proportion of FA associated with dinoflagellates and terrestrial sources as indicated by a high percentage of C₁₈ polyunsaturated FAs (PUFAs). This is the first study to evaluate diets of these two shrimp species using complimentary FA and SI approaches.