Non-dispersive ultra-violet spectroscopic detection of formaldehyde gas for indoor environments

We describe a simple method for detecting formaldehyde using low resolution non-dispersive UV absorption spectroscopy. A two channel sensor was developed, making use of a strong absorption peak at 339 nm and a neighbouring region of negligible absorption at 336 nm as a reference. Using a modulated UV LED as a light source and narrow laser-line filters to select the desired spectral bands, a simple detection system was constructed specifically targeted at formaldehyde. By paying particular attention to sources of noise, a minimum detectable absorbance of 5×10 -5 AU was demonstrated with a 20 s averaging period (as ΔI/I0). The system was tested with formaldehyde finding a limit of detection of 4.3 ppm for a 195 mm gas cell. As a consequence of the low gas flow rates used in our test system, a time period of over 8 min was used in further tests, which increased the minimum detectable absorbance to 2×10 -4 AU, 17 ppm of formaldehyde. The increase was the result of thermal drift caused by unwanted temperature variation of the UV LED and the filters, resulting in a zero uncertainty estimated at 560 ppm °C -1 and 100ppm °C -1 respectively

Impacts of Swiss needle cast on Douglas-fir tree-ring stable isotopes and tree carbohydrate reserves

Understanding the mechanisms of disease in forest pathology is a critical component to learning how to most efficiently manage tree diseases like Swiss needle cast (SNC). SNC is an economically important, fungal disease of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) that is prevalent in coastal areas of the Pacific Northwest. This thesis research provides two contributions to the greater understanding of the pathogenic impacts on plant physiological functioning, or pathophysiology, of SNC on Douglas-fir that will ultimately inform management decisions in Pacific Northwest forests affected by SNC. The primary objectives of this thesis research were: (1) to examine the effects of SNC on Douglas-fir tree-ring stable isotope discrimination of carbon (Δ¹³C) and oxygen (δ¹⁸O) and (2) to evaluate the impact of SNC on tree carbohydrate reserves. Thesis Objective 1- I used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla (Raf.) Sarg.) to evaluate their use as proxies for variation in past SNC infection, particularly in relation to potential explanatory climate factors. Trees were sampled from a site where a fungicide trial took place from 1996 to 2000, which enabled the comparison of years when disease was present and absent, relative to untreated trees which had the infection throughout. Tree-ring Δ¹³C of treated Douglas-fir increased during the treatment period, and was ~1.6 per mil greater than that of untreated Douglas-fir at the end of the years of the fungicide treatment. Both annual growth and tree-ring Δ¹³C increased with treatment such that treated Douglas-fir had values similar to co-occurring western hemlock during the treatment period, which suggests that the use of Δ¹³C in Douglas-fir tree-rings to track SNC disease history may be a practical approach provided a reference species is available to develop a parallel Δ¹³C chronology. There was no difference in tree-ring δ¹⁸O between treated and untreated Douglas-fir. Tree-ring Δ¹³C of diseased Douglas-fir was negatively correlated with relative humidity (RH) during the two previous summers, consistent with increased leaf colonization by SNC under high humidity conditions that then lead to greater disease severity in following years. Thesis Objective 2- The effects of SNC on Douglas-fir carbohydrate reserves were explored to evaluate the extent to which non-structural carbohydrate (NSC) can be mobilized under natural conditions of low water stress and restricted carbon supply in relation to potential demands for growth. Concentrations of starch, sucrose, glucose and fructose were analyzed in twig wood, foliage, and trunk sapwood of 15 Douglas-fir trees expressing a gradient of SNC symptom severity. There were significant negative relationships between disease severity and growth (mean basal area increment, BAI), as well as between disease severity and mean concentration of trunk NSC. The amount of NSC per unit growth (mean NSC/BAI), an index of the relative priority of storage versus growth, increased with disease severity in all three sampled tissues. These results suggest that under reduced carbon supply with SNC, Douglas-fir trees retain NSC at the expense of growth. The crown retains the most NSC, presumably to maintain foliage growth in the spring to compensate for SNC-induced rapid foliage loss in the summer and fall

Aerosol-assisted CVD synthesis, characterisation and gas-sensing application of gold-functionalised tungsten oxide

Tungsten oxide nanoneedles (NNs) functionalised with gold nanoparticles (NPs) have been integrated with alumina gas-sensor platforms using a simple and effective co-deposition method via aerosol-assisted chemical vapour deposition (AACVD) utilising a novel gold precursor, (NH4)AuCl4. The gas-sensing results show that gold NP functionalisation of tungsten oxide NNs improves the sensitivity of response to ethanol, with sensitivity increasing and response time decreasing with increasing amount of gold

Development of Wind Alarm Systems for Road and Rail Vehicles: Presentation of the WEATHER project

The development of a new concept of wind alarm systems for road and rail transportation is presented. The alarm is funded on a risk assessment approach, taking into account wind modelling and prediction, aerodynamic forces, vehicle dynamics

The use of electrochemical sensors for monitoring urban air quality in low-cost, high-density networks

Measurements at appropriate spatial and temporal scales are essential for understanding and monitoring spatially heterogeneous environments with complex and highly variable emission sources, such as in urban areas. However, the costs and complexity of conventional air quality measurement methods means that measurement networks are generally extremely sparse. In this paper we show that miniature, low-cost electrochemical gas sensors, traditionally used for sensing at parts-per-million (ppm) mixing ratios can, when suitably configured and operated, be used for parts-per-billion (ppb) level studies for gases relevant to urban air quality. Sensor nodes, in this case consisting of multiple individual electrochemical sensors, can be low-cost and highly portable, thus allowing the deployment of scalable high-density air quality sensor networks at fine spatial and temporal scales, and in both static and mobile configurations.This work was supported by EPSRC (grant number EP/E002102/1) and the Department for Transport

Plant growth and development in relation to the microclimate of a sorghum/groundnut intercrop

An intercrop of one row of sorghum (Sorghum bicolor (L.) Moench) and three rows of groundnut (Arachis hypogaea (L.)) and sole crops of the two species were grown with limited water supply on an alfisol in central India. The faster growth rate of intercropped sorghum was the result of a greater fraction of light being intercepted rather than a higher efficiency () of conversion of light into dry matter. In intercropped groundnut, there was a strong correlation between the growth rate of each row and the fraction of light it intercepted, and although shading by the sorghum reduced the latter in comparison with the sole crop, was higher. Two patterns of response were evident in the intercropped groundnut. Those involving resource use (light and water) and dry matter production were lowest in the outer two rows and highest in the centre row, while those involving development (e.g. pod numbers) increased from the least shaded row to the most shaded. Competition for water by the more aggressive sorghum was thought to be responsible for the first response, and temperature and water potential gradients caused by differing degrees of shading for the second. The effect of the interaction of these two responses on the harvest index is discussed

A Nairobi experiment in using low cost air quality monitors

Many African cities have growing air quality problems, but few have air quality monitoring systems in place. Low cost air quality sensors have the potential to bridge this data gap. This study describes the experimental deployment of six low cost air quality monitors consisting of an optical particle counter Alphasense OPC-N2 for measuring PM1, PM2.5 and PM10, and Alphasense A-series electrochemical (amperometric) gas sensors: NO2-A43F, SO2-A4, NO-A4 for measuring NO2, NO and SO2 in four schools, the United Nations Environment Program (UNEP) headquarters and a community center in Nairobi. The monitors were deployed on May 1 2016 and are still logging data. This paper analyses the data from May 1 2016 to Jan 11 2017. By examining the data produced by these sensors, we illustrate the strengths, as well as the technical limitations of using low cost sensors for monitoring air quality. We show that despite technical limitations, sensors can provide indicative measurements of air quality that are valuable to local communities. It was also found that such a sensor network can play an important role in engaging citizens by raising awareness about the importance of addressing poor air quality. We conclude that these sensors are clearly a potentially important complement but not a substitute for high quality and reliable air quality monitoring systems as problems of calibration, certification, quality control and reporting remain to be solve

Review of low-cost sensors for indoor air quality: Features and applications

Humans spend the majority of their time indoors, where they are potentially exposed to hazardous pollutants. Within this context, over the past few years, there has been an upsurge of low-cost sensors (LCS) for the measurement of indoor air pollutants, motivated both by recent technological advances and by increased awareness of indoor air quality (IAQ) and its potential negative health impacts. Although not meeting the performance requirements for reference regulatory-equivalent monitoring indoors, LCS can provide informative measurements, offering an opportunity for high-resolution monitoring, emission source identification, exposure mitigation and managing IAQ and energy efficiency, among others. This article discusses the strengths and limitations that LCS offer for applications in the field of IAQ monitoring; it provides an overview of existing sensor technologies and gives recommendations for different indoor applications, considering their performance in the complex indoor environment and discussing future trends

Tree-ring stable isotopes record the impact of a foliar fungal pathogen on CO₂ assimilation and growth in Douglas-fir

Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC infection, particularly in relation to potential explanatory climate factors. We sampled trees from an Oregon site where a fungicide trial took place from 1996 to 2000, which enabled the comparison of stable isotope values between trees with and without disease. Carbon stable isotope discrimination (Δ¹³C) of treated Douglas-fir tree-rings was greater than that of untreated Douglas-fir tree-rings during the fungicide treatment period. Both annual growth and tree-ring Δ¹³C increased with treatment such that treated Douglas-fir had values similar to co-occurring western hemlock during the treatment period. There was no difference in the tree-ring oxygen stable isotope ratio between treated and untreated Douglas-fir. Tree-ring Δ¹³C of diseased Douglas-fir was negatively correlated with relative humidity during the two previous summers, consistent with increased leaf colonization by SNC under high humidity conditions that leads to greater disease severity in following years.Keywords: Swiss needle cast, Stable isotopes, Phaeocryptopus gaeumannii, Pseudotsuga menziesii, Tree-ring

Seasonal carbohydrate dynamics and growth in Douglas-fir trees experiencing chronic, fungal-mediated reduction in functional leaf area

Stored non-structural carbohydrates (NSCs) could play an important role in tree survival in the face of a changing climate and associated stress-related mortality. We explored the effects of the stomata-blocking and defoliating fungal disease called Swiss needle cast on Douglas-fir carbohydrate reserves and growth to evaluate the extent to which NSCs can be mobilized under natural conditions of low water stress and restricted carbon supply in relation to potential demands for growth. We analyzed the concentrations of starch, sucrose, glucose and fructose in foliage, twig wood and trunk sapwood of 15 co-occurring Douglas-fir trees expressing a gradient of Swiss needle cast symptom severity quantified as previous-year functional foliage mass. Growth (mean basal area increment, BAI) decreased by ~80% and trunk NSC concentration decreased by 60% with decreasing functional foliage mass. The ratio of relative changes in NSC concentration and BAI, an index of the relative priority of storage versus growth, more than doubled with increasing disease severity. In contrast, twig and foliage NSC concentrations remained nearly constant with decreasing functional foliage mass. These results suggest that under disease-induced reductions in carbon supply, Douglas-fir trees retain NSCs (either actively or due to sequestration) at the expense of trunk radial growth. The crown retains the highest concentrations of NSC, presumably to maintain foliage growth and shoot extension in the spring, partially compensating for rapid foliage loss in the summer and fall.Keywords: Non-structural carbohydrates, Swiss needle cast, Phaeocryptopus gaeumannii, Growth limitation, Pseudotsuga menziesiiKeywords: Non-structural carbohydrates, Swiss needle cast, Phaeocryptopus gaeumannii, Growth limitation, Pseudotsuga menziesi