Airborne measurements of peroxy radicals using the PERCA technique

The Peroxy Radical Chemical Amplifier (PERCA) technique is a proven method for measurement of ambient levels of peroxy radicals at ground level, but there are no published instances of the technique being used on an aerial platform. Here we describe deployment of a PERCA on the former UK Meteorological Office C-130 Hercules research aircraft. The instrument uses the established method of chemical amplification and conversion of peroxy radicals to nitrogen dioxide (NO2) by doping the sample air-flow matrix with CO and NO, subsequently measuring the NO2 yield with an improved 'Luminox' LMA-3 NO2 detector. NO2 from the amplification chemistry is distinguished from other sources of NO2 reaching the detector by periodically injecting CO approximately 1 s downstream of the NO injection point (termination mode). Chain lengths (CL's) for the amplification chemistry were typically approximately 260 (ground level) to approximately 200 (7,000 m). This variation with altitude is less than the variation associated with the 'age' of the PFA inlet material where the amplification chemistry occurs; CL's of approximately 200 with old tubing to approximately 300 with new clean tubing were typical (ground level values). The CL determinations were made in-flight using an onboard calibration unit based on the 254 nm photolysis of 7.5 to 10 parts per billion (by volume, ppbv) of CH3I in air, producing CH3O2 in a quantitative manner. The noise-equivalent detection limit for peroxy radicals (HO2 + RO2) is 2 parts per trillion (by volume, pptv) at 3,650 m when the background ambient ozone levels are stable, based on a 5 min average of five 30 s amplification cycles and five 30 s termination cycles. This detection limit is a function of several factors but is most seriously degraded when there is large variability in the ambient ozone concentration. This paper describes the instrument design, considers its performance and proposes design improvements. It concludes that the performance of an airborne PERCA in the free troposphere can be superior to that of ground-based instruments when similar sampling frequencies are compared.     

Modelling the initiation and spread of Infectious Pancreatic Necrosis Virus (IPNV) in the Irish salmon farming industry: The role of inputs

Observed emergence of IPNV in farmed Irish salmon is simulated using a model originally developed to analyse the spread of the virus in Scotland [Murray, A.G., 2006a. A model of the spread of infectious pancreatic necrosis virus in Scottish salmon farms 1996–2003. Ecol. Model. 199, 64–72]. IPNV appears to have become established relatively recently in Ireland and the model is altered to explicitly simulate the origin of the spread of the virus. Input to freshwater farms was key to initiation of infection, but modelling suggests that endogenous spread was responsible for much of the subsequent increase in prevalence of IPNV. From the modelling, it is unlikely that direct imports accounted for most IPNV cases. If this is the case, cessation of imports, without a substantial improvement in biosecurity, would be likely to be of only limited effect in controlling IPNV. Marine IPNV prevalence appears to be insensitive to direct interventions in the marine environment (as in the Scottish model). A multi-element control strategy, targeting both endogenous spread and external input of infection and prioritising freshwater sites, but extending to marine sites, would probably now be required to eradicate IPNV from Ireland.     

Do trans-Pacific air masses deliver PBDEs to coastal British Columbia, Canada?

In order to distinguish between ‘local’ and ‘background’ sources of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in coastal British Columbia (Canada) air, we collected samples from two sites: a remote site on western Vancouver Island, and a near-urban site in the Strait of Georgia. Seasonally-integrated samples of vapor, particulate, and rain were collected continuously during 365 days for analysis of 275 PCB and PBDE congeners. While deposition of the legacy PCBs was similar at both sampling sites, deposition of PBDEs at the remote site amounted to 42% (10.4 mg/ha/year) of that at the near-urban site. Additional research into atmospheric circulation in the NE Pacific Ocean will provide more insight into the transport and fate of priority pollutants in this region, but trans-Pacific delivery of PBDEs to the west coast of North America may underlie in part our observations. For example, approximately 40% of >12,000 ten-day back trajectories calculated for the remote site originated over Asia, compared to only 2% over North America.     

A field trial to assess the performance of CO2-supersaturated water injection for residual volatile LNAPL recovery

A pilot scale field trial was conducted to evaluate the recovery of volatile, light non-aqueous phase liquids (LNAPLs) using a novel remediation method termed supersaturated water injection (SWI). SWI uses a patented technology to efficiently dissolve high concentrations of CO₂ into water at elevated pressures. This water is injected into the subsurface resulting in the nucleation of CO₂ bubbles at and away from the injection point. The nucleating bubbles coalesce, rise and volatilize residual LNAPL ganglia. In this study, an LNAPL composed of 103 kg of volatile pentane and hexane, and 30 kg of non-volatile Soltrol was emplaced below the water table at residual saturation. The SWI technology removed 78% of the pentane and 50% of the less volatile hexane. Contaminant mass was still being removed when the system was shut down for practical reasons. The mass removed is comparable to that expected for air sparging but a much smaller volume of gas was injected using the SWI system.     

Reactive uptake of ozone at simulated leaf surfaces: Implications for ‘non-stomatal’ ozone flux

The reaction of ozone (O₃) with α-pinene has been studied as a function of temperature and relative humidity and in the presence of wax surfaces that simulate a leaf surface. The objective was to determine whether the presence of a wax surface, in which α-pinene could dissolve and form a high surface concentration, would lead to enhanced reaction with O₃. The reaction of O₃ itself with the empty stainless steel reactor and with aluminium and wax surfaces demonstrated an apparent activation energy of around 30 kJ mol^?1 for all the surfaces, similar to that observed in long-term field measurements of O₃ fluxes to vegetation. However, the absolute reaction rate was 14 times greater for aluminium foil and saturated hydrocarbon wax surfaces than for stainless steel, and a further 5 times greater for beeswax than hydrocarbon wax. There was no systematic dependence on either relative or absolute humidity for these surface reactions over the range studied (20–100% RH). Reaction of O₃ with α-pinene occurred at rates close to those predicted for the homogeneous gas-phase reaction, and was similar for both the empty reactor and in the presence of wax surfaces. The hypothesis of enhanced reaction at leaf surfaces caused by enhanced surface concentrations of α-pinene was therefore rejected. Comparison of surface decomposition reactions on different surfaces as reported in the literature with the results obtained here demonstrates that the loss of ozone at the earth's surface by decomposition to molecular oxygen (i.e. without oxidative reaction with a substrate) can account for measured ‘non-stomatal’ deposition velocities of a few mm s^?1. In order to quantify such removal, the effective molecular surface area of the vegetation/soil canopy must be known. Such knowledge, combined with the observed temperature-dependence, provides necessary input to global-scale models of O₃ removal from the troposphere at the earth's surface.     

Trace element pollution records in some UK lake sediments, their history, influence factors and regional differences

Sediment cores were taken from six sites across the UK. Apart from Banbury Reservoir in London, all the other sites are relatively remote lakes. Trace elements Pb, Zn, Cu, Cd, Cr, Ni, Sn, As and V, major elements such as Fe, Mn, Ti and Al were analysed, and organic content measured as loss-on-ignition was determined in all of these cores. The result shows that these relatively remote sites have experienced enhanced atmospheric deposition of anthropogenically derived trace elements for over 100 years, and the contamination might start before industrialisation. Trace metal contamination remains the highest level at Banbury Reservoir showing "pollution source" influence. Despite the considerable reduction in atmospheric deposition in recent years, although some of the element concentrations in the surface sediments have declined, they are still much higher than their natural background values. In these sites, trace element pollution records have been influenced by many different factors. Redox condition could affect As distribution in the sediments. Sediment matrix could also affect trace element pollution signal. Apart from direct atmospheric deposition, the distributions of trace elements in the sediments have been affected by forestry activities and catchment erosion, and more contaminated soil in-wash could increase sediment pollution whilst less contaminated soil could dilute sediment pollution. In some sites, data suggest that catchment in-wash is an important source of elements for the lakes.     

Less-invasive autopsy for early pregnancy loss

Autopsy investigations provide valuable information regarding fetal death that can assist in the parental bereavement process, and influence future pregnancies, but conventional autopsy is often declined by parents because of its invasive approach. This has led to the development of less-invasive autopsy investigations based on imaging technology to provide a more accessible and acceptable choice for parents when investigating their loss. Whilst the development and use of more conventional clinical imaging techniques (radiographs, CT, MRI, US) are well described in the literature for fetuses over 20 weeks of gestational age, these investigations have limited diagnostic accuracy in imaging smaller fetuses. Techniques such as ultra-high-field MRI (>3T) and micro-focus computed tomography have been shown to have higher diagnostic accuracy whilst still being acceptable to parents. By further developing and increasing the availability of these more innovative imaging techniques, parents will be provided with a greater choice of acceptable options to investigate their loss, which may in turn increase their uptake. We provide a narrative review focussing on the development of high-resolution, non-invasive imaging techniques to evaluate early gestational pregnancy loss.