The objective of this thesis is to evaluate the sources of the differences between the NO2 satellite retrieval products provided by the Royal Dutch Meteorological Institute (KNMI) and the National Aeronautics and Space Administration (NASA). Ground studies have shown that although both products use the same satellite, these products yield different observations for NO2 tropospheric columns concentrations. This study does not validate either retrieval product, but rather indentifies the main sources for the discrepancy. There are several parameters which allow successful retrieval of NO2 vertical columns. For this study, only the difference between the radiative models and the a priori NO2 chemical transport models were considered relevant. All other parameters, such as cloud properties, slant columns, stratospheric serration and their assumptions, were held constant. Here, the models are referred to by their proprietor's acronym: "TOMRAD" refers to the radiative model used by NASA, "DAK" refers to the radiative model used by KNMI, "TM4" refers to the a priori chemical transport model used by KNMI, and "REAM" refers to the a priori chemical transport model maintained by the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. Mixing these parameters creates four retrievals for comparison. Many significant differences were identified after comparing these four retrievals. First, there are viewing geometry biases between the port side and the starboard side of the satellite retrieval for each swath. These viewing geometry biases lead to artificial periodicities in the retrievals of NO2 tropospheric vertical columns over a specific coordinate or site, such as a city. Furthermore, there were significant differences found after using different a priori NO2 chemical transport models. The low horizontal resolution of TM4 and the satellite retrieval/TM4 coupling effect compared to REAM leads to considerable questioning of the near real time application of the KNMI NO2 retrieval product. Though the TM4 model performs poorly, TM4 retrievals do perform nearly as well as REAM retrievals at capturing day-to-day variability and the spatial variability of the cities used as examples here. The retrievals using TOMRAD outperformed the retrievals using DAK when compared to the high resolution, hourly REAM a priori chemical transport model. In sum, these findings should lead to better optimizations of both the KNMI and NASA retrievals, and thus make their publicly available data products more reliable and accurate for general use.

Knowledge of NOx (NO2 + NO) emissions is useful to understand processes affecting air quality and climate change. Emission inventories of surface NOx have high uncertainties. Satellite remote sensing has enabled measurements of trace gases in the atmosphere over a large regional and temporal scale. Inverse modeling of NO2 observations from satellites can be used to improve existing emissions inventories. This study seeks to understand the difference in two methods of inverse modeling: the mass balance approach and the adjoint approach using the GEOS-Chem chemical transport model and its adjoint. Using both synthetic satellite observations and those derived from the SCIAMACHY satellite instrument, this paper found that the performance of these two inversions was affected by pixel smearing and observational error. Smearing reduced the accuracy of the mass balance approach, while high observational error reduced the accuracy of the adjoint approach. However, both approaches improved the a priori emissions estimate.

South Africa has the largest economy in Africa, with significant mining and metallurgical activities. A large fraction of the mineral assets is concentrated in the Bushveld Igneous Complex (BIC), with the western limb being the most exploited. Although the western BIC is considered to be an air pollution hotspot, inadequate air quality data currently exists for this area. To partially address this knowledge gap, a comprehensive air quality monitoring station was operated for more than two years at Marikana in the western BIC. Basic meteorological parameters, precipitation, Photosynthetic Photon Flux Density (PPFD), trace gas concentrations (SO2, NO, NOx, O3, and CO), physical aerosol parameters (particle number and air ion size distributions, as well as aerosol light absorption) and total PM10 mass concentration were measured. Compared with South African and European ambient air quality standards, SO2, NO2 and CO concentrations were generally below the air quality standards, with average concentrations for the sampling period of 3.8ppb (9.9μg/m³), 8.5ppb (15.9μg/m³) and 230ppb (270μg/m³), respectively. The major source of SO2 was identified as high-stack industry emissions, while household combustion was identified as the predominant source of NO2 and CO. In contrast, O3 exceeded the eight-hour moving average standard (61ppb / 120μg/m³) 322 times per year. The main contributing factor was identified to be the influx of regional air masses, with high O3 precursor concentrations. PM10 exceeded the current South African 24-hour standard (120μg/m³) on average 6.6 times per year, the future 2015 standard (75μg/m³) 42.3 times per year and the European standard (50μg/m³) 120.2 times per year. The PM10 average concentration for the sampling period was 44μg/m³, which exceeded the current European and future (2015) South African annual average standard (40μg/m³), emphasising the PM pollution problem in the western BIC. The main source of PM10 was identified as household combustion. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012

A 10.6 ym C02 laser operating a power range S P 200 watts was used to pump some select vibrational transitions in the NO2 molecule while monitoring the rotational transitions (91/9—'100/10), (232f 22 ~~"*242,23> ' (402,38 "393,37) in the (0, 0, 0) vibrational level and the (8q,8—*"^1,7) rotational transition in the (0, 1, 0) vibrational level. These rotational transitions were monitored by microwave probing to determine how the population of states in the rotational manifolds were being altered by the laser. Coincidences between some components of the V3-V2 band of N02 and the C02 infrared laser lines in the 10 um region appeared to be responsible for the strong interaction between the continuous laser beams and the molecular states.

Mobile devices for the personalized detection of health and environmental hazards are becoming the basis for futuristic sensing technologies. In recent decades, air and environmental pollution levels have risen globally. Therefore, environmental protection must be strengthened by developing sensors that detect pollutants. The monitoring of these pollutants with high spatial coverage requires inexpensive electronic gas sensors and self sustainable sensing systems that can be deployed everywhere. This dissertation reports on technological developments to provide solutions for inexpensive, compact, power efficient, and easily deployable toxic gas sensors and integrated systems using semiconducting metal-oxide thin-film transistors (TFTs). The first part of the dissertation introduces the fabrication and characterization of an amorphous indium gallium zinc oxide (IGZO) TFT as a toxic gas sensor. In contrast to existing metal-oxide gas sensors, which are active either with light activation or at high temperature, the developed IGZO TFT sensors are operable at room temperature and require only visible light activation to revive them after exposure to NO2. IGZO TFT sensors exhibited remarkable selectivity and sensitivity to low concentrations of nitrogen dioxide (NO2). The second part of the dissertation introduces the design and realization of the IGZO-based fully integrated gas detectors. Unlike existing gas-sensing systems, which have discrete hardware for signal conditioning, read-out, and data acquisition, the developed integrated detectors constitute thesemodules integrated using IGZO TFT technology. The integrated detectors detect ambient NO2 gas and generate a digital output that is proportional to the ambient gas concentrations. Two types of integrated gas detectors were developed that differ in their mode of operation and circuitry design. These detectors are scalable and pave the way for portable systems to realize various gas-sensing applications, including smart cities and sustainable ecosystems. The success of personalized monitoring devices relies on the following factors: minimum power consumption, selectivity, and stability under extreme conditions that determine overall performance. One of the best solutions to minimize power consumption in these devices is to have a complementary energy-harvesting feature. Hence, the dissertation concludes with the design of self-powered sensors, which are IGZO sensors with self-powering capabilities. Self-powered sensors are p-n heterojunction sensors, developed using IGZO and hybrid-perovskites.

Background: Air pollution has been associated with adverse health effects for all-cause and specific respiratory morbidity and mortality outcomes. Acute exacerbations of COPD (AE-COPD) accelerate the decline in pulmonary function and are associated with greater mortality, morbidity, health care utilization, and reduced quality of life. Since the 1970 Clean Air Act was implemented, important reductions in air pollution have been achieved, but no safe threshold has been identified. Objectives: The study was planned to evaluate associations between exposure to ambient concentrations of five criteria air pollutants (CO, SO2/, NO2/, ozone, PM2.5/) in Philadelphia, Pennsylvania, and visits to Temple University Hospital for AE-COPD, from January 1, 2005 through March 31, 2007. To identify subgroups with greater susceptibility to air pollution, associations were examined according to age, gender, race, residence, and antibiotic prescription. Methods: Average daily air pollutant concentrations were obtained from the EPA's Air Quality Services Data Mart. Air pollutant exposures were evaluated for the day of the visit (lag0), one and two days preceding the visit (lag1 and lag2), and the average concentration over three days (lag012). Poisson regression provided rate ratios (RRs) to estimate associations between air pollution exposures and AE-COPD hospital visits. Results: Of 1546 hospital visits for AE-COPD, 43% were from persons 65 years or older, 50% of each gender, and 90% from Philadelphia. In single pollutant models, increased RRs were present at all lags for NO2/ (e.g., RR = 2.27 [95%CI: 1.52, 3.38] at lag012) and SO2/ (e.g., RR = 1.70 [95%CI: 1.38, 2.08] at lag012). For PM2.5/, the direct effect was present only during the winter at lag1, lag2, and lag012 (RR = 1.79 [95%CI: 1.08, 2.96]). Inverse associations were present for ozone at all lags (e.g., RR = 0.64 [95%CI: 0.53, 0.76] at lag012). Compared to the cohort as a whole, those ≥ 65 years of age were at greater risk of an AE-COPD hospital visit associated with PM2.5/ and CO at lag012, with NO2/ and SO2/ at lag0 and lag012, but there was no difference in ozone effect. Conclusions: Primary gaseous air pollution exposures (SO2/, CO, NO2/) were associated with increased AE-COPD hospital visits among COPD patients at Temple University Hospital. The effects of SO2/, CO, NO2/, and PM2.5 were greater for the subgroup ≥ 65 years of age compared to the cohort as a whole. Inverse associations with ozone were consistent across subgroups. These results suggest that air quality during the study period was insufficient to protect the health of COPD patients, especially those ≥ 65 years old. Further study is needed to understand generalizability to other populations and to evaluate lower ranges of exposure from current levels of air pollution. / Public Health

<p> Exposure to traffic-related air pollutants has been found to be damaging to human health. Nitrogen dioxide (NO2) levels, commonly used to indicate traffic-related pollution levels, vary significantly over small areas with higher levels found near sources such as major roads and industrial areas. The temporal and spatial variability in NO2 levels is partly caused by fluctuations in meteorological variables, and better understanding of these: meteorological influences can be used to enhance exposure assessment in health effects models.</p> <p> In this study, the interaction between measured hourly NO2 concentrations and climate variables at 11 locations in the Toronto-Hamilton Urban Airshed (THUAS) is examined. Analysis of meteorological data shows that two large urban heat islands (UHI) are present in the THUAS, centred on the downtown areas of Toronto and Hamilton. Lake breezes are found to occur frequently in the region, on up to 50% of summer days at lakeshore locations. These temperature and wind patterns influence NO2 and pollutant distributions. NO2 concentrations are highest in the early morning and late evening. Mean concentrations are highest in winter, although individual 1-hour NO2 concentrations are found to be highest in summer because of higher production rates. Wind direction is the strongest control on hourly NO2 concentration, and temperature and wind speed also have an effect. Seasonal variations in meteorology and emissions mean that the degree of spatial variability in NO2 concentrations changes from season-to-season in the THUAS resulting in variable exposure of urban populations.</p> <p> An attempt to improve an existing Land Use Regression (LUR) model, used for predicting nitrogen dioxide (NO2) concentrations and estimating human exposure, was made by incorporating high resolution interpolated observed up- and downwind effects of wind transport on NO2 concentrations around major roadways. Incorporation of observed wind direction effects in the LUR model slightly improved the accuracy of NO2 concentration estimates in densely populated, high traffic, and industrial/business areas in both Toronto and Hamilton. However the short-term nature of initial NO2 concentration data limits the utility of the model in light of the significant seasonal variation in climate parameters in the THUAS and their influence on NO2 transport and distribution.</p> / Thesis / Master of Science (MSc)

Objectif : Ce travail s’inscrit dans le cadre d’une recherche étiologique sur les leucémies aigues (LA) de l’enfant, pathologies dont les facteurs de risque sont peu connus. Plusieurs hypothèses ont été testées : 1) le rôle protecteur d’une supplémentation maternelle en acide folique avant et pendant la grossesse et l’investigation par une approche gène-candidat du rôle de polymorphismes communs rs1801133 et 1801131 de MTHFR et rs1801394 et rs1532268 de MTRR supposés modifier le métabolisme des folates, 2) l’association entre la profession et des expositions professionnelles maternelles lors de la grossesse, 3) l’existence d’un lien positif avec l’exposition des enfants au trafic routier. Matériel et méthodes : Les données analysées proviennent d’une étude cas-témoins française, ESCALE, basée sur le Registre National des Hémopathies malignes de l’Enfant et réalisée en population générale sur la période 2003-2004. L’échantillon comportait 648 cas de leucémie aiguë lymphoblastique [LAL], 116 cas de leucémie aiguë non lymphoblastique [LANL], et 1681 témoins de moins de 15 ans. L’échantillonnage a été stratifié sur l’âge et le sexe. Les données ont été recueillies auprès des mères à l’aide d’un questionnaire téléphonique standardisé, identique pour les cas et les témoins. Les génotypes ont été obtenus par génotypage à haut débit, pangénomique pour les cas et à façon pour les témoins, et par imputation pour les polymorphismes non génotypés. Le géocodage des adresses et des indicateurs dérivés de données d’émission de trafic ont permis d’estimer l’exposition des enfants au trafic routier. Les odds ratios (OR) ont été estimés à l’aide de modèles de régression logistique non conditionnelle, incluant les facteurs de confusion potentiels. Résultats : Le risque de LA était significativement inversement associé à une supplémentation maternelle en acide folique avant ou pendant la grossesse (OR=0.4 [0.3-0.6]). Aucun des polymorphismes génétiques de MTHFR et de MTRR n’était associé au risque de LA. Cependant, le fait d’être à la fois porteur homozygote des allèles variants de l’un des polymorphismes de MTHFR, et porteur de deux allèles variants des polymorphismes de MTRR était positivement associé au risque de LA (OR=1.6 [0.9-3.1]). Nous n’observions pas d’interaction entre MTHFR, MTRR et une supplémentation maternelle en acide folique. Des associations positives et significatives on été mises en évidence entre le risque de LA et des expositions auto-déclarées professionnelles maternelles pendant la grossesse, aux teintures de cheveux (OR=3.0 [1.7-5.2]), à des peintures ou vernis et/ou colles (OR=1.5 [1.1-2.2]), et à des rayonnements ionisants (OR=2.4 [1.3-4.6]). Cependant, ces associations étaient limitées aux fréquences d’exposition de moins d’1 heure par semaine et peuvent refléter une sur-déclaration chez les cas. L’exposition maternelle professionnelle aux pesticides n’était pas associée aux LA dans notre étude.Les LA étaient significativement associées à des concentrations élevées de NO2 de fond liées au trafic estimées au lieu de résidence (OR=1.2 [1.0-1.5]) et avec la présence de routes à fort trafic dans un rayon de 500 m centré sur ce lieu (OR=2.0 [1.0-3.6]). Nous observions une association significative entre les LA et une densité élevée de routes à fort trafic dans un rayon de 500 m (OR=2.2 [1.1-4.2]), avec une tendance linéaire positive significative de l’association des LAL avec la longueur totale de routes à fort trafic dans un rayon de 500 m.Conclusion : Cette thèse apporte des arguments en faveur du rôle protecteur d’une supplémentation maternelle périconceptionnelle en acide folique. Elle suggère également un rôle des polymorphismes de MTHFR et MTRR dans le risque des LA, sans interaction toutefois avec la supplémentation. Enfin, elle renforce l’hypothèse que vivre près de routes à fort trafic pourrait augmenter le risque de LA. / Objectives: This work investigated three hypotheses related to the etiology of childhood acute leukemia (AL):1) maternal folic acid supplementation before or during pregnancy reduces AL risk, accounting for the SNPs rs1801133 (C677T) and rs1801131 (A1298C) in MTHFR and rs1801394 (A66G) and rs1532268 (C524T) in MTRR, assumed to modify folate metabolism, 2) maternal occupation and occupational exposure during pregnancy may be link to LA 3) traffic is a source of environmental exposures, including benzene, which may be related to childhood leukemia. Methods: The data were obtained from the national registry-based case-control study ESCALE, carried out in France in 2003-2004. The ESCALE study included 764 cases and 1681 controls less than 15 years old and the controls were frequency matched with the cases on age and gender. The data were collected by a standardized telephone interview of the mothers. Various indicators of exposure to traffic and pollution were determined using the geocoded addresses at the time of diagnosis for the cases and of interview for the controls. The genotypes were obtained using high-throughput platforms and imputation for untyped polymorphisms. CITP-68 classification was used to classify maternal occupation during pregnancy. Indicators of the distance from, and density of, main roads and background traffic NO2 concentrations data were used. Odds ratio (OR) were estimated using unconditional regression models adjusted for potential confounders. Results: AL was significantly inversely associated with maternal folic acid supplementation before and during pregnancy (OR=0.4 [0.3–0.6]). MTHFR and MTRR genetic polymorphisms were not associated with AL. However, AL was positively associated with homozygosity for any of the MTHFR polymorphisms and carriership of both MTRR variant alleles (OR=1.6 [0.9–3.1]). No interaction was observed between MTHFR, MTRR, and maternal folate supplementation. Significant positive associations were observed between childhood AL and self-reported maternal occupational exposures during pregnancy to hair dye (OR=3.0 [1.7-5.2]), to paints or polishs and/or glues (OR=1.5 [1.1-2.2]), and to ionising radiations (OR=2.4 [1.3-4.6]). However, these associations were limited to exposure frequencies of less than 1 hour by week. Maternal occupational exposure to pesticides during pregnancy was not related to AL. AL was significantly associated with high estimates of traffic NO2 concentration at the place of residence(OR=1.2 [1.0-1.5]) and with the presence of a heavy-traffic road within 500 meters compared to the absence of a heavy-traffic road in the same area (OR=2.0 [1.0-3.6]). There was a significant association between AL and a high density of heavy-traffic roads within 500 meters in comparison to the reference category with no heavy-traffic road within 500 meters (OR=2.2 [1.1-4.2]), with a significant positive linear trend of the association of AL with the total length of heavy-traffic road within 500m. Conclusion: The study findings support the hypothesis that maternal folic acid supplementation may reduce the risk of childhood AL. The findings also suggest that the homozygous genotype for any of the MTHFR variants and carrying both MTRR variants could be a risk factor for AL. Finally, the results support the hypothesis that living close to heavy-traffic roads may increase the risk of childhood leukemia.

Au cours des dernières années, les efforts de recherche et de développement pour les capteurs de gaz se sont orientés vers l'intégration de nanomatériaux afin d'améliorer les performances des dispositifs. Ces nouvelles générations promettent de nombreux avantages notamment en matière de miniaturisation et de réduction de la consommation énergétique. Par ailleurs, la détection sous gaz (sensibilité, seuil de détection, temps de réponse, ...) s'en retrouve améliorée à cause de l'augmentation du ratio surface/volume de la partie sensible. Ainsi, de tels capteurs peuvent être intégrés dans des systèmes de détections ultrasensibles, autonomes, compactes et transportables. Dans cette thèse, nous proposons d'utiliser des réseaux verticaux de nanofils semi-conducteurs pour créer des dispositifs de détection de gaz hautement sensibles, sélectifs, avec une faible limite de détection (de l'ordre du ppb) et intégrable dans des technologies CMOS, tout en étant générique et adaptable à plusieurs types de matériaux afin de discriminer plusieurs gaz. Une première partie expose la mise au point d'un procédé grande échelle, reproductible, compatible avec l'industrie actuelle des semi-conducteurs (CMOS), pour obtenir un capteur basé sur une architecture 3D à nanofils. Le dispositif est composé de deux contacts symétriques en aluminium à chaque extrémité des nanofils, dont l'un est obtenu par l'approche dite du " pont à air ", permettant la définition d'un contact tridimensionnel au sommet du nanofil. La seconde partie présente les performances sous gaz des dispositifs développés et les mécanismes de fonctionnement. Le capteur démontre des performances record en matière de détection du dioxyde d'azote (30% à 50 ppb) en comparaison à l'état de l'art (25% à 200 ppb). De plus, cette approche permet de mesurer de très faibles concentrations de ce gaz (< 1 ppb) de manière sélective, dans des conditions proches des conditions réelles : humidité (testé jusqu'à 70% d'humidité) et mélange avec d'autres gaz plus concentrés et la réversibilité du capteur est naturelle et se fait à température ambiante sans nécessité des conditions particulières. / In recent years, efforts of research and development for gas sensors converged to use nanomaterials to optimize performance. This new generation promises many advantages especially in miniaturization and reduction of energy consumption. Furthermore, the gas detection parameters (sensitivity, detection limit, response time ...) are improved due to the high surface/volume ratio of the sensitive part. Thus, this sensors can be integrated in ultrasensitive detection systems, autonomous, compact and transportable. In this thesis, we propose to use 3D semiconductor nanowires networks to create highly sensitive and selective gas sensors. The objective of this work is to provide a highly sensitive sensor, featuring a low detection limit (in the ppb range) and embeddable in CMOS devices. In addition process is generic and adaptable to many types of materials to discriminate several gas and converge to electronic nose. The first part of the dissertation is based on development of a large scale, reproducible, compatible with Si processing industry and conventional tools (CMOS), to obtain a sensor based on a 3D nanowire architecture. The device is composed by two symmetrical aluminum contacts at each extremity of the nanowires, including a top contact done by air bridge approach. The second part of this work presents the gas performances of components and working mechanisms associated. A very high response (30%) is obtained at 50 ppb of NO2, compare to the state of the art, 25% reached for 200 ppb. This approach can measure selectively very low concentrations of gas (<1 ppb) in real working conditions: moisture (tested up to 70% moisture) and mixing with other more concentrated gas (interfering gas). In addition, the reversibility of the sensor is natural and occurs at room temperature without requiring specific conditions.

Yttria stabilized Zirconia (8YSZ) is an extensively used solid electrolyte, which finds applications in electrochemical sensors, solid oxide fuel cells and gate oxide in MOSFETs. Recent studies report that YSZ thin films are better performers than their bulk counterparts, in terms of ionic conductivity even at moderate temperatures. YSZ thin films also attract attention with the scope of device miniaturization. However, most of the studies available in the literature on YSZ thin films focus mainly on their electrical characterization. In this work, YSZ thin films were deposited, characterized and possible use of sensors were evaluated. In the present work, 8 mol% yttria stabilized zirconia thin films were deposited using RF magnetron reactive sputtering under different deposition conditions. Films with thicknesses ranging from few tens to few hundreds of nanometres were deposited. The deposited films were subjected to morphological, structural, compositional and electrical characterizations. Deposition and annealing conditions were optimized to obtain dense, stoichiometric and crystalline YSZ thin films. The ionic conductivity of 200 nm nanocrystal line thin film was found to be two orders of magnitude higher than the bulk. The ionic conductivity increased with the decrease in film thickness. Compositional analyses of a set of YSZ thin films revealed free surface yttrium segregation. The free surface segregation of dopants can locally alter the surface chemistry and influence the oxygen transfer kinetics across the electrode-electrolyte interface. Although number of reports are available on the segregation characteristics in YSZ bulk, no reports are available on yttria segregation in YSZ thin film. Hence, this work reports detailed investigations on the free surface yttria segregation in YSZ thin films using angle resolved X-ray photoelectron spectroscopy (XPS). Influence of annealing temperature, film thickness, annealing time, and purity on the segregation concentration was determined. It was found that the most important factor that determines the segregation was found to be the target purity. The segregation depth profile analysis showed that the segregation layer depth was proportional to segregation concentration. Free surface segregation reduced the ionic conductivity of the YSZ thin films roughly about a factor. However, segregation did not affect the film’s morphology, grain size, crystallinity and activation energy. The difference in ionic conductivity observed in the segregated and clean YSZ films suggests that dopant free surface segregation could also be one of the reasons for the variable ionic conductivity reported in the literature. For using YSZ in miniaturized devices, micro-structuring of YSZ is important. It has been reported that the wet etching techniques available for YSZ were not repeatable and do not etch annealed YSZ samples. Reactive ion etching (RIE) is better suited for YSZ patterning due to its capability to offer high resolution, easy control and tenable anisotropic/isotropic pattern transfer for batch processing. Although reports are available on the dry etching of zirconia and yttria thin films, no studies were reported on the dry etching of YSZ thin films. In this work, inductively coupled reactive ion etching (ICP-RIE) using fluorine and chlorine chemistries were employed to etch YSZ thin films. Optimized etching conditions were identified by varying different process parameters like, type of gas, gas flow rate, RF power, ICP power, chamber pressure and carrier wafer in the ICP-RIE process. Optimized conditions were chosen by examining the etch depth, composition analyses before and after etch using XPS, selectivity towards SiO2 (which is the most common buffer layer) and surface roughness. Etch chemistries involved in a particular plasma (SF6, Cl2 and BCl3) were discussed with the help of surface composition and etch thicknesses. The results showed that etching YSZ with BCl3 plasma at optimized conditions yielded best results through oxygen-scavenging mechanism. A maximum etch rate of 53 nm/min was obtained in BCl3 plasma using PECVD Si3N4 carrier wafer at an ICP power of 1500 W, RF power of 100 W, chamber pressure of 5 mTorr with 30 sccm BCl3 flow. Sensing devices were designed by employing YSZ thin film as solid electrolyte and nickel oxide and gold thin film as sensing and reference electrodes, respectively to evaluate the possible use of YSZ thin film in miniaturized NO2 sensor. The electrodes were deposited in inter-digitated pattern. Two types of electrodes were designed with different number of fingers in symmetric and asymmetric configurations. The NO2 sensing was performed in the concentration range of 25 to 2000 ppm at three different temperatures, 673, 773 and 873 K in mixed potential and impedance metric modes. The mixed potential type measurements were carried out only for asymmetric cell in two different electrode configurations. The impedance metric type measurements were carried out for both symmetric and asymmetric cells in two different electrode configurations. Preliminary NO2 sensing experiments in both the types of measurements revealed that in devices with electrodes having more fingers were better in performance. In mixed potential type sensors, sensitivity was measured as the amount of voltage generated when the sensor was exposed to a test gas. The generated voltage was found to be proportional to the logarithm of NO2 concentration in the entire measurement range (50 to 2000 ppm) with the regression fitting parameter, adj.R2 around 0.97 to 0.99 in all the cases. A maximum potential of 271 mV was measured with 2000 ppm NO2 at 873 K. The response and recovery times of the sensors were sensitive to the operating temperature. In impedance metric mode, the sensitivities were measured as the variation in the low frequency phase angle (∆ φ) when the gas concentration is changed. The frequency range of the measurement was from 0.01 Hz to100 kHz. The response time in the impedance metric sensors was comparable to that of mixed potential sensors. But the recovery time in impedance metric sensors was much was slower than the mixed potential type for all the concentrations. The sensors showed linear response only in a narrow range of 50 to 500 ppm with regression fitting value, R2 around 0.98 in all the cases. Above 500 ppm, the sensitivity value was observed to be saturated. From the gas sensing studies performed on the miniaturized sensors, it was found that the mixed potential type sensing mode is better than the impedance metric type in YSZ thin film based devices. However detailed interference gas studies were needed before drawing any conclusion. In summary, the studies presented in the work have contributed to the understanding of free surface yttria segregation behaviour in YSZ thin films. Micromachining conditions were optimized for both pristine and annealed YSZ thin films. Suitability of YSZ thin film based miniaturized NO2 gas sensor was evaluated.