Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 204-209). Available also in a digital version from Dissertation Abstracts.

The present dissertation covers three research topics on catalytic environmental emissions control, including (1) aging and regeneration mechanisms of Rh- and Pd- model three-way catalysts (TWC) for gasoline automotive emission control, (2) catalytic methane emissions abatement from natural gas vehicles, and (3) scale-up of CO₂ capture and methanation using dual functional catalytic materials. The study resulted in two peer-reviewed publications, two future papers and one patent application which is currently under review. Modern TWC use supported two separate catalyst layers on a monolith containing one Pd and the other Rh for the emissions control of CO, HC and NOₓ. The rhodium (Rh) metallic component (active for NOₓ reduction) experiences the most severe oxidative thermal deactivation (forming inactive Rh³⁺) during fuel cutoff, an engine mode (e.g., at downhill coasting) used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by the reduction of the Rh³⁺ with H₂ generated through steam reforming catalyzed by residual Rh⁰ sites. The present thesis reports the effects of the deactivation and regeneration processes on the activity, stability and structural properties of 0.5% Rh/Al₂O₃ and 0.5% Rh/Ce_xO_y-ZrO₂ (CZO) as model catalysts. Both materials are used to varying extents in modern TWC. A very brief introduction of three-way catalysis and system considerations will be presented. During simulated fuel cutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al₂O₃. Catalyst characterization techniques including BET surface area, CO chemisorption, temperature programmed reduction, and x-ray photoelectron spectroscopy, transmission electron microscopy, scanning-electron microscopy, and x-ray diffraction measurements were applied to examine the role of metal-support interactions in each catalyst system. For Rh/Al₂O₃, strong metal-support interactions leading to the formation of a stable rhodium aluminate (Rh(AlO₂)_y) complex dominates during fuel cutoff, resulting in more difficult catalyst regeneration (reduction). For Rh/CZO, Rh sites were partially oxidized to Rh₂O₃ and were relatively easy to be reduced to active Rh⁰ during regeneration. Moderate Pd and support sintering of Pd-Ce_xO_y is experienced upon aging, but with a minimal effect on the catalyst activity. Cooling in air, following aging, was not able to reverse the metallic Pd sintering by re-dispersing to PdO. Unlike the aged Rh-TWCs, reduction via in situ steam reforming (SR) of exhaust HCs was not effective in reversing the deactivation of aged Pd/Al₂O₃, but did show a slight recovery of the Pd activity when CZO was the carrier. The Pd⁺/Pd⁰ and Ce³⁺/Ce⁴⁺ couples in Pd/CZO are reported to promote the catalytic SR by improving the redox efficiency during the regeneration, while no such promoting effect was observed for Pd/Al₂O₃. A suggestion is made for improving the catalyst performance. The use of natural gas for vehicle applications is growing in popularity due to advanced fracking technology. Exhaust methane has been excluded from regulations since it does not participate in photochemical reactions. New vehicle environmental regulations are expected for controlling methane emissions given their contribution to the greenhouse gas effects. Methane is extremely resistant to oxidation when the natural gas-fueled engine operates in the stoichiometric mode with a supported Rh-Pd three-way catalyst (TWC). Furthermore, vehicles will still operate with fuel cutoff (for enhanced fuel economy), resulting in thermal oxidative deactivation (1050 °C) of the Rh metal in TWC to inactive Rh³⁺, resulting in a loss of both NOₓ and methane abatement activity. When the engine returns to the slightly rich mode, H₂ generated by methane steam reforming does not readily occur to reduce and regenerate the Rh. We report a solution to methane emissions abatement by catalytic reforming of an injected aqueous solution of ethanol into the simulated exhaust stream in TWC mode, which generates sufficient H₂ to regenerate especially Rh by reducing Rh³⁺ to its metallic active state. Conventional CO₂ capture and sequestration (CCS) in aqueous alkaline solutions is a very energy-intensive process with relative unstable performance and low efficiency especially for power plant effluents, and therefore there is a need for new approaches to control green house gas emissions of CO₂. Here we report on progress with an advanced technology involving CO₂ adsorption from flue gas and synthetic natural gas production, via methanation, both performed at the same temperature with the addition of renewable H₂ and by using a dual functional material (DFM). The stored H₂ used is produced by water electrolysis during those times when solar, wind, and other alternative energies generate excess power out of phase with the direct use of the electricity. The DFM is composed of nano-dispersed CaO (or Na₂CO₃) and Ru metal supported on γAl₂O₃ carrier, respectively functioning as the CO₂ adsorbent and methanation catalyst. The present paper focuses on a laboratory scale-up study by using a simulated flue gas and 5%Ru,10%CaO/Al₂O₃ and 5% Ru,10%Na₂CO₃/Al₂O₃ DFM samples. The effects of DFM preparation methods, Al₂O₃ carrier materials (with different shapes and properties), and adsorption and methanation conditions (feed compositions, flow rates, reaction temperatures) on the DFM performance were examined. Samples were prepared using chloride precursor salts and showed stable performance under pseudo scale-up conditions, with SASOL TH100 Al₂O₃ (with the highest BET surface area and pore volume/radius among the support materials) exhibiting the best performance. Compared to Ru-CaO, Ru-Na₂CO₃ based DFM materials showed improved CO₂ utilization and methanation production. Reaction conditions were explored to find optimized CO₂ adsorption and methanation.

This paper critically analyzes the implementation of compressed natural gas and the ways in which it creates discourse in urban Bolivia. The rapidly developing nation is keen on making ubiquitous use of compressed natural gas a reality by issuing subsidies, citing increased mobility, savings, and environmental stewardship as the primary motives. Currently, eight out of every 10 public vehicles in Bolivia are powered by compressed natural gas. Through semi-structured interviews, questionnaires and secondary data collection, this paper elucidates the transitional process of building a natural gas-based transport network through discursive governance. This work draws on the critical discourse analysis literature to dissect disaggregated modal preference data, government documents, and news articles collected in Santa Cruz, Latin America's second fastest growing city. Moreover, this paper identifies and examines the ways in which the counter-discourse impacts the transformation of the country’s energy matrix. Results show that Bolivian automobile owners are reluctant to convert their automobiles, despite reduced transportation costs, stating that minimal compressed natural gas infrastructure exists outside of urban areas, and the conversion damages their vehicles’ motor. Additionally, the research reveals that automobile owners are currently the main beneficiaries, though respondents who do not posses an automobile speak more favorably of natural gas. Finally, this research illustrates that the compressed natural gas-oriented policies encourage personal automobile use that continues to drive socio-spatial segregation of Santa Cruz’s residents. Thus, the compressed natural gas discourse helps shape the urban landscape by persuading the public to consume domestically extracted and manufactured natural gas.

Over the past decade, public concerns have grown over America's energy use and production. Pushes towards more environmentally friendly and sustainable sources of energy have moved out of fringe politics and into mainstream political discourse. Advances in drilling technology and increased exploration of shale gas plays have made natural gas more available and accessible. The abundance of natural gas has led to its growing role in the U.S. electric production and has provided the United States with an opportunity to become a net exporter of energy in the near future. The availability of natural gas, coupled with uncertainty in the liquid petroleum market, has prompted stakeholders to search out additional uses for this low-cost energy source. The result has been a large-scale effort to encourage the use of natural gas-based fuel within the trucking industry. Commercial long-haul trucks and truck fleets are a v prime target of these efforts. The number of natural gas fueling stations around the country is increasing, and there are growing investments in new technologies and government incentives to retrofit and upgrade the nation's trucking fleet, making the logistics of a large-scale switch from a liquid petroleum-based fuel to natural gas much less complicated. Through a detailed analysis of natural gas trucks, fueling infrastructure, and case studies this report seeks to reach conclusions over the role natural gas vehicles (NGVs) should play in the future U.S. transportation system. Chapter 1 provides a brief introduction to natural gas. Chapter 2 discusses the current state of natural gas in the United States. Chapter 3 provides an overview of natural gas vehicle and infrastructure technology. Chapter 4 discusses marketplace NGV adoption factors. Chapter 5 deals with benefits of adoption and policy options for expansion of NGVs. Chapter 6 provides an overview of current federal, state and local policies and incentives. Chapter 7 discusses barriers and opportunities for NGV adoption. The report synthesizes and concludes that natural gas trucking offers the U.S. a cheaper alternative to liquid petroleum while promoting environmental sustainability and economic prosperity. / text

This dissertation consists of three essays. The first essay estimates a demand function for compressed natural gas as a fuel substitute to diesel fuel for firms with hybrid fleets. The data is from the Energy Information Administration, for the years 1989 to 2009, for 47 states. Results show that an increase of $0.10 in the price of diesel fuel will increase compressed natural gas demand by 5.59%. The second essay focuses on regional trade agreements (RTAs). A number of studies have found that RTAs significantly increase members' trade flows. While recent studies have begun to explore the reasons for this, none have examined whether the RTA trade effect varies systematically with the number and type of policy areas covered by the agreement. While the empirical trade literature has shed considerable light on the trade-creating ability of RTAs (Grant and Lambert, 2008), much less is known about why these agreements are so successful. In this study, we draw on a new database from the World Trade Organization of trade policy areas covered by RTAs to examine whether the degree of trade liberalization is an important determinant of the RTA trade effect. An augmented, theoretically consistent gravity equation is developed to explore the effects of RTAs on trade, conditional on the policy areas they include. In particular, we investigate two policy areas that are particularly important for agricultural trade, sanitary and phytosanitary measures (SPS) and technical barriers to trade (TBT). The results suggest that harmonization of non-tariff measures inside RTAs matters: Agreements that liberalize these policies increase members' agricultural trade by an additional 62 percent compared to agreements that do not. We conclude that studying the components of RTAs -- in particular, the policy areas covered by these agreements -- is important when analyzing the determinants of RTA trade effects. The third essay uses Bayesian Model Averaging (BMA) to study the effect of membership in the General Agreement on Tariffs and Trade (GATT), the predecessor to the World Trade Organization (WTO), and the WTO on trade flows. Existing GATT/WTO literature is not univocal as to whether membership in the GATT/WTO increases trade flows. In this study, Bayesian model averaging (BMA) is used in the presence of theoretical uncertainty to address whether membership in the GATT/WTO plays a role in the gravity model. Several datasets are examined: a dataset from a previous study; and two datasets compiled for this study, world trade and agricultural trade. Results show, for all three sets of data, that membership in the GATT/WTO does belong in the gravity equation and increases trade flows. / Ph. D.

No description available.

This paper analyses the purchase and operation of vehicles on compressed natural gas. It contains a definition of Compressed Natural Gas (CNG) and discusses the various phases of its use in transport. It indicates the differences of this alternative fuel compared to traditional fuel such as gasoline or diesel. Then it focuses on the main reasons to support the use of compressed natural gas transport and talks about the legislation which has a major role in the development of alternative fuels. Then it specifies the disadvantages which can be associated with its use in transport. The last section includes an analysis on the specific example of the RWE CZ Group, which compares the different costs for compressed natural gas vehicles and vehicles which run on conventional fuel. Specifically the cost per kilometer of vehicle, CO2 emission and purchase price are given for comparison.

Esta dissertação desenvolveu duas análises de natureza diferente, mas complementares, uma vez que são unidas por uma mesma questão. Esta questão diz respeito à utilização do gás natural veicular em substituição ao óleo diesel em ônibus urbanos. O autor argumenta que, devido a suas características técnicas, o gás natural pode contribuir para a promoção de um transporte mais sustentável, mesmo que o gás natural seja um combustível igualmente não renovável, como o óleo diesel. Na primeira análise desenvolvida, utiliza-se uma metodologia bottom-up para demonstrar os ganhos ambientais que podem ser alcançados ao se substituir o óleo diesel por gás natural em ônibus urbanos. Adota-se a cidade de São Paulo como estudo de caso. Esses ganhos ambientais manifestam-se tanto na redução das emissões de poluentes locais, como material particulado, monóxido de carbono e óxidos de enxofre, conduzindo a melhoras importantes na qualidade de vida das pessoas que sofrem os efeitos nocivos dessas emissões (usuários ou não do transporte público urbano), como, também, no declínio das emissões de gases de efeito estufa, especialmente o dióxido de carbono, levando a benefícios ambientais globais. Os resultados amparam o uso do gás natural em ônibus como uma estratégia de maior sustentabilidade no plano ambiental. Já, na segunda análise desenvolvida, a pesquisa levanta as questões seguintes: Quais outros parâmetros influenciam a decisão de se promover a substituição de combustíveis em ônibus urbanos? Quais critérios explicam as escolhas por distintos combustíveis substitutos? As respostas a essas questões são obtidas através de uma Análise Qualitativa Comparativa (AQC). A pesquisa comparou 39 cidades em todo o mundo, que adotaram combustíveis substitutos ao óleo diesel em ônibus urbanos, incluindo o gás natural, biocombustíveis, eletricidade e hidrogênio. Os resultados atestam que as cidades de fato utilizam-se da substituição de combustíveis para tornar o transporte mais sustentável. Observa-se que a opção pelo gás natural é acolhida na maioria dos casos analisados como uma opção com vantagens ambientais e economicamente mais atrativa. A principal razão para sua eventual não adoção identifica-se com a insegurança energética. Algumas cidades receiam depender de um combustível que, assim como o petróleo (do qual o óleo diesel é um derivado), também está afeito a importantes suscetibilidades geopolíticas. A conclusão do trabalho reforça a importância do gás natural como um combustível ambientalmente mais amigável, e que pode contribuir na busca das cidades por sistemas de transporte público mais sustentáveis, especialmente em grandes áreas metropolitanas. Olhando, especificamente, o caso da cidade de São Paulo, com desdobramentos para o Brasil como um todo, a pesquisa enfatiza a necessidade de se superar barreiras regulatórias, e de se comprovar vantagens econômicas e de segurança de suprimento energético, para que o gás natural possa confirmar-se atrativo e mais sustentável aos olhares dos gestores dos sistemas de transporte público urbanos. Esses temas não podem ser deslembrados ao se propor uma política mais racional de combustíveis para o transporte público das grandes cidades brasileiras. / This work has developed two analyzes of different kinds, but complementary, since they are united by the same issue. This issue relates to the use of compressed natural gas to replace diesel fuel in city buses. The author argues that, due to its technical characteristics, natural gas can contribute to the promotion of more sustainable transport, even though the gas is a non-renewable fuel, such as diesel oil. In the first in-depth analysis, a bottom-up methodology is used in order to demonstrate the environmental benefits that can be achieved by replacing the diesel oil with natural gas in urban buses. The city of São Paulo is adopted as a case study. These environmental gains are manifested both in reducing emissions of local pollutants such as particulate matter, carbon monoxide and sulfur oxides, leading to significant improvements in quality of life of people suffering the harmful effects of the emissions (both public urban transport users and non-users), and also in the decline of emissions of greenhouse gases, especially carbon dioxide, leading to global environmental benefits. The results bolster the use of natural gas buses as a more sustainable strategy in environmental terms. In the second developed analysis, the research raises the following questions: What other parameters influence the decision to encourage the substitution of urban buses in fuels? What criteria explain the choices for different substitute fuels? The answers to these questions are obtained from a Qualitative Comparative Analysis (QCA). The study compared 39 cities across the world that have adopted fuel substitutes to diesel fuel in urban buses, including natural gas, biofuels, electricity and hydrogen. The results show that in fact, cities are use fuel shifting as a way to turn its transport system more sustainable. It is observed that the option for natural gas is considered, in most analyzed cases, as an option with environmental advantages and economically more attractive. The main reason for natural gas non-adoption was identified as energy insecurity. Some cities fear depending on a fuel that, like petroleum (of which diesel oil is a derivative), is also sensitive to relevant geopolitical issues. The conclusion of the work reinforces the importance of natural gas as a more environmentally friendly fuel, and can contribute to the promotion more sustainable public transport systems in cities, especially in large metropolitan areas. Looking specifically at the case of the city of São Paulo, as well as considering Brazil as a whole, the research emphasizes the need to overcome regulatory barriers, and to prove economic benefits and energy supply security, so that the natural gas can confirm is attractive and more sustainable to the eyes of managers of urban public transport systems. These issues cannot be forgotten in order to propose a more rational policy of fuel for public transport in large Brazilian cities.

Esta dissertação desenvolveu duas análises de natureza diferente, mas complementares, uma vez que são unidas por uma mesma questão. Esta questão diz respeito à utilização do gás natural veicular em substituição ao óleo diesel em ônibus urbanos. O autor argumenta que, devido a suas características técnicas, o gás natural pode contribuir para a promoção de um transporte mais sustentável, mesmo que o gás natural seja um combustível igualmente não renovável, como o óleo diesel. Na primeira análise desenvolvida, utiliza-se uma metodologia bottom-up para demonstrar os ganhos ambientais que podem ser alcançados ao se substituir o óleo diesel por gás natural em ônibus urbanos. Adota-se a cidade de São Paulo como estudo de caso. Esses ganhos ambientais manifestam-se tanto na redução das emissões de poluentes locais, como material particulado, monóxido de carbono e óxidos de enxofre, conduzindo a melhoras importantes na qualidade de vida das pessoas que sofrem os efeitos nocivos dessas emissões (usuários ou não do transporte público urbano), como, também, no declínio das emissões de gases de efeito estufa, especialmente o dióxido de carbono, levando a benefícios ambientais globais. Os resultados amparam o uso do gás natural em ônibus como uma estratégia de maior sustentabilidade no plano ambiental. Já, na segunda análise desenvolvida, a pesquisa levanta as questões seguintes: Quais outros parâmetros influenciam a decisão de se promover a substituição de combustíveis em ônibus urbanos? Quais critérios explicam as escolhas por distintos combustíveis substitutos? As respostas a essas questões são obtidas através de uma Análise Qualitativa Comparativa (AQC). A pesquisa comparou 39 cidades em todo o mundo, que adotaram combustíveis substitutos ao óleo diesel em ônibus urbanos, incluindo o gás natural, biocombustíveis, eletricidade e hidrogênio. Os resultados atestam que as cidades de fato utilizam-se da substituição de combustíveis para tornar o transporte mais sustentável. Observa-se que a opção pelo gás natural é acolhida na maioria dos casos analisados como uma opção com vantagens ambientais e economicamente mais atrativa. A principal razão para sua eventual não adoção identifica-se com a insegurança energética. Algumas cidades receiam depender de um combustível que, assim como o petróleo (do qual o óleo diesel é um derivado), também está afeito a importantes suscetibilidades geopolíticas. A conclusão do trabalho reforça a importância do gás natural como um combustível ambientalmente mais amigável, e que pode contribuir na busca das cidades por sistemas de transporte público mais sustentáveis, especialmente em grandes áreas metropolitanas. Olhando, especificamente, o caso da cidade de São Paulo, com desdobramentos para o Brasil como um todo, a pesquisa enfatiza a necessidade de se superar barreiras regulatórias, e de se comprovar vantagens econômicas e de segurança de suprimento energético, para que o gás natural possa confirmar-se atrativo e mais sustentável aos olhares dos gestores dos sistemas de transporte público urbanos. Esses temas não podem ser deslembrados ao se propor uma política mais racional de combustíveis para o transporte público das grandes cidades brasileiras. / This work has developed two analyzes of different kinds, but complementary, since they are united by the same issue. This issue relates to the use of compressed natural gas to replace diesel fuel in city buses. The author argues that, due to its technical characteristics, natural gas can contribute to the promotion of more sustainable transport, even though the gas is a non-renewable fuel, such as diesel oil. In the first in-depth analysis, a bottom-up methodology is used in order to demonstrate the environmental benefits that can be achieved by replacing the diesel oil with natural gas in urban buses. The city of São Paulo is adopted as a case study. These environmental gains are manifested both in reducing emissions of local pollutants such as particulate matter, carbon monoxide and sulfur oxides, leading to significant improvements in quality of life of people suffering the harmful effects of the emissions (both public urban transport users and non-users), and also in the decline of emissions of greenhouse gases, especially carbon dioxide, leading to global environmental benefits. The results bolster the use of natural gas buses as a more sustainable strategy in environmental terms. In the second developed analysis, the research raises the following questions: What other parameters influence the decision to encourage the substitution of urban buses in fuels? What criteria explain the choices for different substitute fuels? The answers to these questions are obtained from a Qualitative Comparative Analysis (QCA). The study compared 39 cities across the world that have adopted fuel substitutes to diesel fuel in urban buses, including natural gas, biofuels, electricity and hydrogen. The results show that in fact, cities are use fuel shifting as a way to turn its transport system more sustainable. It is observed that the option for natural gas is considered, in most analyzed cases, as an option with environmental advantages and economically more attractive. The main reason for natural gas non-adoption was identified as energy insecurity. Some cities fear depending on a fuel that, like petroleum (of which diesel oil is a derivative), is also sensitive to relevant geopolitical issues. The conclusion of the work reinforces the importance of natural gas as a more environmentally friendly fuel, and can contribute to the promotion more sustainable public transport systems in cities, especially in large metropolitan areas. Looking specifically at the case of the city of São Paulo, as well as considering Brazil as a whole, the research emphasizes the need to overcome regulatory barriers, and to prove economic benefits and energy supply security, so that the natural gas can confirm is attractive and more sustainable to the eyes of managers of urban public transport systems. These issues cannot be forgotten in order to propose a more rational policy of fuel for public transport in large Brazilian cities.

Made available in DSpace on 2016-03-15T19:26:25Z (GMT). No. of bitstreams: 1 Barbara Susana Barbosa de Araujoprot.pdf: 2856714 bytes, checksum: 2d649f4e75619acdc07f8887a5c9bb99 (MD5) Previous issue date: 2015-02-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The starting point for the construction of this study was the perception that the current societal behavior and business management models do not provide the balance needed for the continuation of environmental resources essential to human survival. The challenges to achieve the widespread sustainable development are immense and, for many, utopian. This research was conducted after admitting that the production of knowledge is one of the guiding pillars of the advancement of the discussions which enable a boost in understanding and engagement within society in favor of a less unsustainable future. This study sought to understand to what extent there is a relationship between the environmental awareness of taxi drivers in São Paulo and the use of natural gas for their vehicles, compared to the survey of the factors that stimulate and discourage the use of this fuel considered less pollutant. The choice of researching on the use of Natural Gas Vehicles (NGV) as an energy source was due to the fact that in Brazil the use of other clean energy sources in the transport sector is extremely incipient. We sought to identify which in practice, are perceived as attributes that encourage and / or inhibit drivers to use NGV. In addition, we sought to understand whether taxi drivers, apart from the technical and economic developments, were also motivated by an environmental concern to collaborate or reinforce the choice of a less polluting fuel than traditional ethanol and gasoline. The results obtained by our descriptive quantitative research, with 73 taxi drivers in São Paulo, preceded by a qualitative exploratory study. Factors related to the financial benefits of the use of CNG were confirmed as the main attractions for using this type of fuel; whereas the necessary investment to adapt the vehicle to the supply of natural gas was appointed as the main to its use. When analyzing the results, it can be concluded that, because there is no evidence that environmental awareness is an important attribute in the decision of taxi drivers to use cleaner fuel, it is necessary to have a greater incentive to use this power source, or any other offering less potential offensive worsening of urban pollution and consequent respiratory diseases, to which the population is subject to. The stimuli may be a result of, among others, tax exemptions, already practiced in some Brazilian municipalities. / A percepção de que os modelos atuais de comportamento da sociedade e de gestão de negócios não proporcionam o equilíbrio necessário para continuidade dos recursos ambientais essenciais à sobrevivência humana foi o ponto de partida para construção deste estudo. Os desafios para se atingir o tão difundido desenvolvimento sustentável, são imensos e, para muitos, utópicos. Essa pesquisa foi concebida por admitir-se que a produção do conhecimento é um dos pilares norteadores para o avanço dos debates capazes de impulsionar a compreensão e o engajamento da sociedade em prol de um futuro menos insustentável. Objetivou-se compreender em que medida existe relação entre a consciência ambiental dos taxistas do município de São Paulo e a utilização do gás natural em seus veículos, face ao levantamento dos fatores que estimulam e dos que desestimulam a utilização desse combustível tido como menos poluente. A escolha pela utilização do gás natural veicular (GNV) como fonte de energia pesquisada se deu pelo fato de que no Brasil a utilização de outras fontes de energia limpa no setor de transporte é extremamente incipiente. Buscou-se identificar o que na prática é percebido como atributos que incentivam e/ou inibem os motoristas a usarem o GNV. Além disso, buscou-se entender se, afora as motivações de cunho técnico-econômico havia, entre os taxistas, preocupação ambientais que colaborassem ou reforçassem a escolha por um combustível menos poluente do que os tradicionais etanol e gasolina. Os resultados foram fruto de uma pesquisa quantitativa descritiva realizada com 73 motorista de táxis do município de São Paulo, precedida de um estudo qualitativo exploratório. Os fatores relacionados às vantagens financeiras decorrentes do uso do GNV foram confirmados como os maiores atrativos para uso desse tipo de combustível; ao passo que, o investimento para a adaptação dos veículos ao abastecimento do GNV, foi apontado como o principal obstáculo a sua utilização. Através da análise dos resultados, pode-se concluir que, por não haver evidências de que a consciência ambiental é um atributo relevante na decisão dos taxistas pela utilização de um combustível menos poluente, faz-se necessário que haja maior estímulo ao uso dessa fonte de energia, ou de qualquer outra que ofereça menor potencial ofensivo ao agravamento da poluição urbana e das consequentes doenças respiratórias, as quais a população está sujeita. Os estímulos podem ser fruto, entre outros, da isenção de impostos, já praticada em alguns municípios brasileiros.