Microsensor technologies based on nitride semiconductor materials were developed as options for improved exhaust gas sensors in diesel exhaust systems. The main goals were to develop new sensors that can meet the requirements given by Peugeot PSA to meet upcoming EU emissions regulations for NO, NO2, and NH3 detection. Two different sensor technologies were developed based on Schottky junction and high electron mobility transistor (HEMT) devices. Novel materials such as BGaN and BGaN/GaN superlattice structures are explored. For each device, a comprehensive analytical model is developed and simulations are carried out to optimize and design the sensor devices. Materials growth is then conducted for the different semiconductor layers, followed by materials characterizations to ensure high quality materials. Device prototypes are fabricated using various materials and functional layer designs. For device testing, an experimental setup is developed. Our experimental results show excellent sensitivity; we also report selectivity between NO and NO2 for the first time for these types of devices. Finally, we modify our devices for other sensing applications such as the detection of other harmful gases and pollutants in liquid environments.

No description available.

The overall aim of this thesis was to validate diffusive samplers for measurements of nitrogen dioxide (NO2) and nitrogen oxides (NOx). The Willems badge was validated for NO2 measurements both in laboratory tests and in field tests (Paper I-II). The sampling rate was 40.0 mL/min for ambient air concentrations and 46.0 mL/min for higher concentrations. No effects of different factors on sampling rate were found except for a reduced sampling rate at low wind velocity. The results of the laboratory validation were confirmed in field tests in ambient air and with personal sampling. The correlation between diffusive samplers and the reference monitor was good for ambient measurements. In conclusion, the Willems badge performs well at wind velocities down to 0.3 m/s, and this makes it suitable for personal sampling but less suitable for measurements in indoor air where the wind velocity is lower. Paper III reports about the field validation of the Ogawa diffusive samplers. Absolute humidity and temperature were found to have the strongest effect on sampling rate with lower uptake rates at low absolute humidity or temperature. The sampling rates above 0 °C were 8.6 mL/min for NO2 and 9.9 mL/min for NOx. NO2 and NOx concentrations that were determined using the manufacturer’s protocol were either underestimated or overestimated. The agreement between concentrations measured by the Ogawa sampler and the reference monitor was improved when field-determined sampling rates were used to calculate concentrations. Paper IV is based on a study with the aim of assessing the exposure of the Swedish general population to NO2 and some carcinogenic substances. The surveys were performed in one of five Swedish cities every year. In each survey, personal measurements of NO2 and some carcinogenic substances were conducted on 40 randomly selected individuals. In the study presented in this thesis, the NO2 part of the study is in focus and results were available for eight surveys conducted across the five cities. The estimated arithmetic mean concentration for the general Swedish population was 14.1 μg/m3. The exposure level for NO2 was higher for smokers compared with non-smokers, and the NO2 exposure levels were higher for people who had gas stoves at home or who were exposed at their workplace. The exposure was lower for those who had oil heating in their houses.

In order to fulfil the requirements in the EURO VI standard, regulating emissions from heavy duty vehicles, the exhaust aftertreatment system needs to maintain its efficiency for at least seven years or 700 000 km. In diesel applications the diesel oxidation catalyst (DOC) is located closest to the engine and is thus the most vulnerable to poisoning contaminants, such as phosphorus originating from fuel and oil additives, which deactivates the catalyst. An idea to reduce the impact from phosphorus impurities (recently patented by Scania CV) is to place a low-cost sacrificial substrate, consisting of one or more pillared clay mineral (PILC) with high affinity for phosphorus, upstream the aftertreatment system in order to protect and thus increase the lifetime of the catalytic components which contain platinum group metals. In this work one commercially available and four custom made PILCs, comprising of two conventional type PILCs and two of the type porous clay heterostructures (PCH), were evaluated. The PILCs were exposed to a phosphorus-containing gaseous mixture using a lab-scale experimental setup in order to determine their phosphorus sorption potential. The PILC materials exhibit potential to function as sacrificial substrates for phosphorus in the intended application. It was indicated to be a correlation between increasing iron content (wt%) and increasing phosphorus sorption capability. The most promising material was the custom made Al,Fe-pillared saponite, which was up to twice as effective in trapping phosphorus as the DOC. The commercial sample, the Al-pillared montmorillonite, was only about as efficient as the DOC.

The development of multimode absorption spectroscopy (MUMAS) for multi-species detec- tion and its potential for process control or environmental monitoring is reported. The simultaneous detection of CO and CO2 is demonstrated in a proof-of-principle experiment for applications in industrially relevant gas species monitoring. The technique of MUMAS is extended to the near infrared in order to detect these and other industrially relevant species. A laser was designed and constructed to emit a multimode spectrum in the region of 1.57um to take advantage of the spectral overlap of the second vibrational overtone of CO and the combination band 3ν1 + ν3 of CO2. The laser consisted of a semi-confocal cavity employing an Er:Yb glass chip as the gain medium. The laser was pumped by a 1W laser diode at 980nm and emitted up to 30mW in a bandwidth of 180GHz. The laser emitted between 6-10 modes depending upon the selective cavity length. Mode spacings varied between 18GHz to 33GHz with an individual mode linewidth of less than 8MHz. The laser modes were simultaneously scanned using a piezo-electric transducer (PZT) in order to modulate the cavity length at frequencies between 1Hz and 10Hz. A system for linearizing the MUMAS spectra with respect to frequency was devised based on a transmission spectra of a confocal Fabry-Perot etalon. Refinements to the MUMAS fitting code were developed to improve the computational efficiency. An initial demonstration of MUMAS on a known gas mixture of CO and CO2 was per- formed. The ratio of CO:CO2 concentrations in the gas mixture was measured with an accuracy of 0.4% which was within the supplier’s quoted uncertainty. MUMAS is then applied to the detection of CO and CO2 concentrations in exhaust gas produced by a 1.3 litre 4-cylinder turbo-charged spark ignition engine. Relative and absolute concentrations were derived from MUMAS signals and values compared to measurements using a 4-gas analyser. Concentrations of CO and CO2 were measured using MUMAS to a precision of 0.17% and 0.23% respectively compared to less than 0.1% for the 4-gas analyser. Ratios of CO and CO2 were determined with a precision of 0.28 using MUMAS compared to 0.11 with the 4-gas analyser. The detection limit of CO was found to be 1486ppm in these circumstances. Finally a discussion is presented of potential improvements arising from wavelength mod- ulation spectroscopy and cavity enhancement techniques.

Student Number : 9900051W - MSc dissertation - School of Chemical and Metallurgical Engineering - Faculty of Engineering and the Built Environment / When specifying materials for use in exhaust systems, it is imperative that they exhibit sufficient corrosion resistance for the specific conditionsto which exhaust components are exposed, since up to 80% of all failures is attributed to corrosion and oxidation. It is therefore neccesary to establish the corrosion behaviour of the materials in conditions and environments to which the exhausts would typically come into contact with. Most car manufacturers, exhaust manufacturers and material providers have specific corrosion testing methods which they use to determine the corrosion resistance of candidate materials, but there appears to be no standard procedure. A summary comparing all the existing systems is given in section 2.7. The corrosion testing methods utilise a wide range of conditions, testing temperatures and stages. However, careful investigation of the tests show some similarities, and it was possible to identify eleven key tests, that cover internal corrosion, external corrosion and oxidation for both diesel and petrol engines. Eight of these tests were used to rank the corrosion and oxidation resistance of selected stainless steels, namely AISI type 304, 321, 409, 434 and DIN 1.4509. It appears that the austenitic stainless steels perform better in the cold end conditions, while the ferritic types are more resistant in the hot end high temperature conditions. Of all the eight test performed, only the electrochemical tests for external corrosion of cold end components did not give reproducible results. The rest of the tests could be used to screen materials for exhaust system applications. In the internal condition of the cold end, the results of the elctrochemical tests indicated that they can be used as a possible replacement for the long exposure tests. The key tests also highlighted the the presence of NH4+ ions in an exhaust gas is benificial to the corrosion resistance od stainless steels in internal cold end application. Its inhibiting effect was more pronounced for the ferritic stainless steels. The project indicated that external corrosion due to salt environments is not the major cause of the failure of cold end components, but rather that internal corrosion due to the condensate is the most detrimental.

<p> </p><p>Introduction:<strong> </strong>Significant changes in the global ecosystem, together with a potential shortfall in oil resources, have stimulated intense interest in the development of other sources of energy, and most particularly biofuels since these are basically considered to be less harmful to human health than petroleum-based fuels. However, information about the impact of biofuel-derived vehicle emissions on human health is limited and incomplete<strong>. </strong></p><p> </p><p>Aim of the study:<em><strong> </strong></em>To identify those biofuels that are less detrimental to human health on the basis of published results from toxicological and chemical studies of vehicle emission products.</p><p> </p><p>Tasks of the study: To review systematically all conventional and alternative fuels used in internal combustion engines, to identify all known toxic emission products formed by such fuels, to review their toxic effects on human health, and to analyse the data collected in order to develop conclusions concerning the possible health benefits deriving from the use of alternative fuels.</p><p> </p><p>Materials and methods: In order to fulfil the requirements of a complete, comprehensive and up-to-date review of the toxic effects of automotive exhaust, an extensive search of official scientific data sources has been performed. Relevant publications were retrieved from public domain databases with a toxicological focus such as Toxcenter and CAplus, as well as from the websites of the US<em> </em><em><em>Environmental Protection Agency</em></em><em> </em>and the US <em><em>Agency for Toxic Substances and Disease Registry</em></em><em><strong>.</strong></em><strong> </strong>Keywords<strong> </strong>employed in the literature search were: petrol, gasoline, diesel exhaust, emission, biofuel, biogas, biodiesel, bioethanol, bioalcohol, toxicity, methanol and ethanol. A total of 295 references were initially selected relating to the period 1962 to 2008, and 142 of these presented titles and abstracts that met the main inclusion criteria, i.e. describing toxicological and epidemiological studies in humans. In cases where eligible studies relating to the goals and tasks of the review were limited or not available, some <em>in vitro</em> or <em>in vivo</em> toxicological studies involving animal models were included.</p><p> </p><p>Results:<strong> </strong>In comparison with petroleum diesel, the emissions derived from biodiesel contain less particulate matter, carbon monoxide, total hydrocarbons and other toxic compounds including vapour-phase C1-C12 hydrocarbons, aldehydes and ketones (up to C8), selected semi-volatile and particle-phase polycyclic aromatic hydrocarbons (PAHs). Whilst sulphur-containing compounds appear to be undetectable in biodiesel, nitrogen oxide and a soluble organic fraction comprising unregulated pollutants including the “aggregated toxics” (i.e., formaldehyde, acetaldehyde, acrolein, benzene, 1,3-butadiene, ethylbenzene, <em>n</em>-hexane, naphthalene, styrene, toluene and xylene) are present at elevated levels. Toxicological studies have shown that the mutagenicity of exhaust particles from biodiesel is normally lower than those obtained from petroleum diesel, however, rapeseed oil-derived biodiesel exhibits toxic effects that are 4-fold greater than petroleum diesel. Such enhanced toxicity is probably caused by the presence of carbonyl compounds and unburnt fuel. The toxicity of highly volatile components of biofuel exhaust has not yet been evaluated accurately. A substantial portion of these compounds was apparently lost in the process of preparing the test samples used for the assays (during the evaporation). The overall recoveries of these compounds have not been evaluated and the accuracy of the sample preparation method has not been validated. Hence, it could be that the cytotoxic effect of biodiesel exhaust is higher than that reported. Moreover, compared with fossil diesel, fuel derived from rapeseed oil emits particulate matter with increased mutagenic effects. Epidemiological investigations of the effects of biofuels on humans are very sparse but have revealed dose-dependent respiratory symptoms following exposure to rapeseed oil biodiesel, although the observed differences between this fuel and petroleum diesel are not significant. Such data, however, give rise to serious concerns about the future usage of this plant material as a replacement for established diesel fuels. Combustion of alcohol-based fuels leads to a reduced formation of photochemical smog in comparison with gasoline or diesel, however, the emission of aldehydes (officially classified as carcinogenic or potentially carcinogenic) is several times higher. The toxicity of the exhaust emissions of gasoline-fuelled engines is generally significantly greater than that of alcohol-burning engines. However, some harmful effects from ethanol blends might be expected, such as enhanced emissions of carcinogenic PAHs and increased ozone-related toxicity associated with the high level of aldehydes emitted. The use of ethanol–diesel fuel blends gives rise to increases in regulated exhaust emissions and, possibly, to greater emissions of aldehydes and unburnt hydrocarbons. The most promising fuels, in terms of reduced toxicity and genotoxicity of exhaust emissions, are methanol-containing blends. However, the emission from these fuels still contains formaldehyde, which is a carcinogen. The use of biogas can significantly reduce emissions of total PAHs and formaldehyde and, consequently, the risk of lung toxicity. On the other hand, the emissions of particulate matter by compressed natural gas, and the mutagenic potencies of the exhaust, are similar to those associated with gasoline and diesel fuels<strong>. </strong></p><p> </p><p>Conclusions: The use of biofuel is currently viewed very favourably and there are suggestions that the exhaust emissions from such fuel are less likely to present risks to human health in comparison with gasoline and diesel emissions. However, the expectation of a reduction in health effects based on the chemical composition of biodiesel exhaust is far from reality. Thus, although toxicological evidence relating to the effects of biofuels on humans is sparse, it is already apparent that emissions from the combustion of biofuel and blends thereof with petroleum-based fuels are toxic. In addition to the regulated toxic compounds, such as total hydrocarbons, carbon monoxide, nitrogen oxides, particulate matter and polycyclic aromatic hydrocarbons, biofuel emissions contain significant amounts of various other harmful substances that are not regulated, e.g. carbonyls (including formaldehyde, acetaldehyde, benzene, 3-butadiene, acrolein, etc.). Whilst biofuels may be potentially less damaging to human health than petroleum fuels, considerable harmful effects must still be expected. Substitution of conventional fuel by biofuel decreases the concentration of regulated toxic pollutants in vehicle exhaust, but increases the concentration of some unregulated toxic pollutants emitted from on-road engines. Generally, the toxicity of biofuels decreases in the order biodiesel>biogas>ethanol>=methanol. In this respect, methanol produced by the oxidation of biogas appears to represent an alternative fuel that exhibits the least potential for damage to human health, however, this alcohol represents a source of formaldehyde pollution and is carcinogenic.</p><p>.</p><p> </p>

A system intended to detect, classify, and track radioactive sources in moving vehicle traffic is under development at Lawrence Livermore National Laboratory (LLNL). This system will fuse information from a network of sensor suites to provide real time tracking of the location of vehicles emitting gamma and/or neutron radiation. This work examined aspects of the source terms of interest and applicable gamma detection technologies for passive detection of emitted gamma radiation. The severe restriction placed on the length of count due to motion of the source is presented. Legitimate gamma sources expected in traffic are discussed. The requirement to accurately classify and discriminate against these "nuisance" sources and cost restraints dictate the choice of NaI(Tl) detectors for this application. The development of a capability to automatically analyze short duration, low signal-to-noise NaI(Tl) spectra collected from vehicles passing a large, stationary detector is reported. The analysis must reliably discriminate between sources commonly transported in motor vehicles and alert on the presence of sources of interest. A library of NaI(Tl) spectra for 33 gamma emitting sources was generated with MCNP4B Monte Carlo modeling. These simulated spectra were used as parent distributions, from which multiple realizations of short duration spectra were sampled. Principal component analysis (PCA) of this data set yielded eigenvectors that enable the conversion of unknown spectra into principal component space (PCS). An algorithm using least squares fitting of the positions of library sources in PCS as basis functions, capable of identifying library nuclides in unidentified spectra, is reported. Analysis results for experimental spectra are compared against those achieved using simulated spectra. A valuable characteristic of this method is its ability to identify sources despite unknown shielding geometries. The successful identification of radionuclides and false identification rates found were excellent for the signal levels involved. For many of the sources, identification performance against experimental spectra was somewhat poorer than found using simulated spectra. The results demonstrate that the PCA-based algorithm is capable of high success rates in identifying sources in short duration, low signal-to-noise NaI(Tl) spectra. / Graduation date: 2001

Biomass-fed cogeneration units and waste incinerators have the advantages of producing efficiently heat and power and of reducing the amount of CO2 emitted per produced energy. However, they produce toxic polychlorinated VOCs (dioxins), CO and NOx. This thesis aims at developing a catalytic system for the total oxidation of chlorinated VOCs that: i) convert efficiently chlorinated VOCs below 250 °C and ii) resist to the exhaust co-pollutants (H2O, CO, NOx). Moreover, this thesis aims at having a complete understanding of the catalytic mechanism. Part I demonstrated that VOx/TiO2 based catalysts are very efficient in the total oxidation of chlorobenzene (taken as a model molecule). In particular, they proved to be highly resistant against deactivation. Moreover, Part I established that the addition of secondary phases producing VOx-WOx/TiO2 or VOx-MoOx/TiO2 induces a synergetic effect that improves the performances. Furthermore, the replacement of a classical TiO2 by a sulfated one improves the catalytic activity. In Part II, the investigation of the co-pollutants influence on the catalysts performances demonstrated their quite good resistance. Indeed, the presence of CO does not induce any deactivation of the catalysts while NOx induces a huge improvement of the catalysts ability to destroy chlorinated VOCs. This beneficial effect is explained by the in situ production of a strong oxidant (NO2) that speeds up the reoxidation of the reduced VOx sites. Nevertheless, H2O vapor can affect negatively the catalyst activity when present in a high concentration. Part III, by revisiting catalytic and characterization results exposed in Part I and II, demonstrated that the catalytic mechanism proceeds in four steps: i) adsorption of chlorinated VOCs on Brønsted sites, ii) VOx redox sites give some of their lattice oxygen atoms to oxidize the aromatic ring producing H2O and COx, iii) reoxidation of the VOx reduced sites thanks to the gas stream oxidant (O2) and iv) retrieving of the chlorine from the surface. The second and third steps compose a Mars and van Krevelen mechanism and the third one is the mechanism rate limiting step. Our work shows that the performances can be improved by tuning the redox properties of the VOx phases: i) improvement of the reducibility and ii) stabilization of the vanadium oxidation level above a limit value, estimated around 4.87.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xiii, 112 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 107-112).