HOx observations over West Africa during AMMA: impact of isoprene and NOx

Aircraft OH and HO2 measurements made over West Africa during the AMMA field campaign in summer 2006 have been investigated using a box model constrained to observations of long-lived species and physical parameters. "Good" agreement was found for HO2 (modelled to observed gradient of 1.23 ± 0.11). However, the model significantly overpredicts OH concentrations. The reasons for this are not clear, but may reflect instrumental instabilities affecting the OH measurements. Within the model, HOx concentrations in West Africa are controlled by relatively simple photochemistry, with production dominated by ozone photolysis and reaction of O(1D) with water vapour, and loss processes dominated by HO2 + HO2 and HO2 + RO2. Isoprene chemistry was found to influence forested regions. In contrast to several recent field studies in very low NOx and high isoprene environments, we do not observe any dependence of model success for HO2 on isoprene and attribute this to efficient recycling of HOx through RO2 + NO reactions under the moderate NOx concentrations (5–300 ppt NO in the boundary layer, median 76 ppt) encountered during AMMA. This suggests that some of the problems with understanding the impact of isoprene on atmospheric composition may be limited to the extreme low range of NOx concentrations

Solvent processing of PMMA and COC chips for bonding devices with optical quality surfaces

Many prototype microfluidic devices are manufactured by some form of micromachining or injection molding which often leaves poor quality surface. This work presents a simple method that both significantly reduces surface roughness of microfluidic chips and at the same time is used to bond devices. The method has been tested on devices made from poly(methyl methacrylate) (PMMA) and cyclic olefin copolymer (COC). The technique uses a solvent vapour exposure process which creates an irreversible bond between two substrates. It also re-flows the material, producing surfaces with optical quality

Autonomous microfluidic sensors for nutrient detection applied to nitrite, nitrate, phospate, manganese and iron

We present the design, fabrication, analysis and characterisation of autonomous high accuracy and sensitivity microfluidic nutrient sensors. A stand-alone sensor platform with integrated sub-systems is demonstrated, which is portable and capable of in-situ reagent-based nutrient analysis. The system is based on a low cost optical detection method, together with an automated microfluidic delivery system that is able to detect nitrite (e.g.) with a Limit of Detection (LOD) of 14nM. The platform was operated in-situ at Southampton Dockhead for 37 hours, performing 284 measurements

Emerging organic contaminants in groundwater

Emerging organic contaminants (ECs) are compounds now being found in groundwater from agricultural, urban sources that were previously not detectable, or thought to be significant. ECs include pesticides and degradates, pharmaceuticals, industrial compounds, personal care products, fragrances, water treatment by-products, flame retardants and surfactants, as well as ‘life-style’ compounds such as caffeine and nicotine. ECs may have adverse effects on aquatic ecosystems and human health. Frequently detected ECs include the anti-epileptic drug carbamazepine, the antibiotic sulfamethoxazole, the anti-inflammatories ibuprofen and diclofenac, and caffeine, as well as pesticide degradates. This means there will be challenges in the future in order to address these ECs and to minimise their impact on drinking water and ecosystems. In the coming decades, more ECs are likely to have environmental standards defined, and therefore a better understanding of environmental behaviour remains a priority

HO[subscript x] observations over West Africa during AMMA: impact of isoprene and NO[subscript x]

Aircraft OH and HO[subscript 2] measurements made over West Africa during the AMMA field campaign in summer 2006 have been investigated using a box model constrained to observations of long-lived species and physical parameters. "Good" agreement was found for HO[subscript 2] (modelled to observed gradient of 1.23 ± 0.11). However, the model significantly overpredicts OH concentrations. The reasons for this are not clear, but may reflect instrumental instabilities affecting the OH measurements. Within the model, HO[subscript x] concentrations in West Africa are controlled by relatively simple photochemistry, with production dominated by ozone photolysis and reaction of O([superscript 1]D) with water vapour, and loss processes dominated by HO[subscript 2] + HO[subscript 2] and HO[subscript 2] + RO[subscript 2]. Isoprene chemistry was found to influence forested regions. In contrast to several recent field studies in very low NO[subscript x] and high isoprene environments, we do not observe any dependence of model success for HO[subscript 2] on isoprene and attribute this to efficient recycling of HO[subscript x] through RO[subscript 2] + NO reactions under the moderate NO[subscript x] concentrations (5–300 ppt NO in the boundary layer, median 76 ppt) encountered during AMMA. This suggests that some of the problems with understanding the impact of isoprene on atmospheric composition may be limited to the extreme low range of NO[subscript x] concentrations

Probe Technology for the Direct Measurement and Sampling of Ellsworth Subglacial Lake

The direct measurement and sampling of Ellsworth Subglacial Lake is a multidisciplinary investigation of life in extreme environments and West Antarctic ice sheet history. The project's aims are (1) to determine whether, and in what form, microbial life exists in Antarctic subglacial lakes and (2) to reveal the post-Pliocene history of the West Antarctic Ice Sheet. A U.K. consortium has planned an extensive logistics and equipment development program that will deliver the necessary resources. This will include hot water drill technology for lake access through approximately 3.2 km of ice, a probe to make measurements with sensors and to collect water and sediment samples, and a percussion corer to acquire an ˜3–4 m sediment core. This chapter details the requirements and early stages of design and development of the probe system. This includes the instrumentation package, water samplers, and a mini gravity corer mounted on the front of the probe. Initial design concepts for supporting equipment required at the drill site to deploy and operate the probe are also described. A review of the literature describing relevant technology is presented. The project will implement environmental protection in line with principles set out by the Scientific Committee on Antarctic Research