Alcohol- and gasohol-fuels: a comparative chamber study of photochemical ozone formation

Abstract

Compostos orgânicos voláteis (COV) tem papel significativo no processo de formação do smog fotoquímico. Os fotooxidantes são formados na atmosfera quando os COV reagem com óxidos de nitrogênio em presença da luz solar e radicais OH. Em áreas urbanas, veículos são uma importante fonte de COV e NO x para a atmosfera, tanto pela queima quanto por evaporação de combustíveis. Neste trabalho são comparados dois tipos de combustível atualmente usados no Brasil -etanol hidratado (95% v/v) e gasool (uma mistura de 22-24% de etanol anidro em gasolina) -em termos de precursores na formação de ozônio na atmosfera de cidades urbanas. Os experimentos foram feitos durante a primavera e verão de 2001/2002 e, em cada um, foram preenchidas duas bolsas de Teflon com cada um dos combustíveis, respectivamente, e altas razões iniciais [COV]/ [NO], sendo a seguir as mesmas expostas à luz solar. Tanto a formação de ozônio quanto os perfis de concentração de NOx foram medidos diretamente com o uso de analisadores contínuos de ozônio e NO/NO 2 /NOx, respectivamente Os resultados mostraram que para os mesmos volumes iniciais de combustível em cada bolsa, as concentrações máximas de ozônio eram em média 28% maiores para o álcool do que para o gasool. Além disso, o processo de formação do ozônio iniciava-se antes para o gasool mas, uma vez iniciado em ambos os combustíveis, a taxa de formação tendia a ser duas vezes maior para o álcool, em comparação ao gasool. Tais observações indicam a necessidade de estudos mais detalhados, a respeito do papel das emissões derivadas de evaporação e combustível não queimado, nos processos de formação de oxidantes fotoquímicos na atmosfera, com atenção especial aos aspectos cinéticos. Isto é particularmente importante para o caso do Brasil, considerando-se a contribuição substancial dessas emissões para o inventário de hidrocarbonetos (HC) e COV, provenientes de fontes móveis em grandes cidades, e uma possível retomada do Programa Brasileiro de Biocombustíveis, a qual levaria a um aumento nas concentrações atmosféricas de etanol.Volatile organic compounds (VOC) play a significative role on the process of formation of photochemical smog. Photooxidants are formed in the atmosphere when VOC react with nitrogen oxides (NOx), in the presence of sunlight and OH radicals. In urban areas, vehicle fuels constitute an important source of VOC and NOx emissions to the atmosphere, either by burning or evaporative losses. This work is concerned with a comparative study of two types of light-duty vehicular fuels presently used in Brazil -namely gasohol (a mixture 22-24% of anhydrous ethanol in gasoline) and hydrated ethanol (95% v/v) -as potential precursors for ozone formation in the atmosphere of urban cities. The experiments were conducted during the spring and summer of 2001/2002. In each one, two Teflon chambers were filled, respectively, with each fuel, at high initial [VOC] to [NO] ratios and exposed to the sunlight. Ozone formation, as well as NOx concentration profiles were measured directly using ozone and NO/N...

Reduction in local ozone levels in urban São Paulo due to a shift from ethanol to gasoline use

“…33,[59][60][61] One such study, which adopts a smog chamber approach, finds that ethanol resulted in around 30% more ozone than gasoline E22-E24. 62 This study is supported by a recent detailed atmospheric chemistry modeling study, 60 which concludes that powering vehicles with ethanol E85 versus gasoline would increase ozone concentrations from 7 to 40 ppb for the conditions studied, and also increase ambient levels of formaldehyde, acetaldehyde, and peroxyacetyl nitrate. Such modeling studies 60,61 seem to be contradicted by other experimental observations that show decreases in ozone levels and the number of smog days when ethanol was added to fuels.…”

Biodiesel: an overview

“…In addition, the ozone formation process showed a tendency to start earlier for gasohol but, once started, its concentration increased up to two times faster than for alcohol fuel. 98 From a perspective of the air quality in large urban centres, especially those to which public transportation is largely dependent on heavy-duty diesel vehicles, as is the case of the majority of Brazilian cities, several studies have pointed to the fact that biodiesel burning, either pure or in mixtures with diesel, can reduce the emissions of carbon monoxide (CO), particulate matter (PM), total hydrocarbons (THC) and sulphur compounds, although quite different conclusions can also be found related to other substances, since an increase in NO x and SOF (soluble organic fractions) emissions is also reported. [99][100][101][102][103][104][105][106][107][108] Despite this, it is unquestionable that biodiesel has almost no sulphur and aromatics and, although CO 2 emissions could be almost at the same levels as those of mineral diesel, its renewable characteristics by cultivation of vegetal sources make it a sink for the atmospheric CO 2 .…”

Temperature measurements by oh lif and chemiluminescence kinetic modeling for ethanol flames

“…In addition, a photograph of the burner and its heating system used to generate the premixed ethanol flames ( Figure 1S), a scheme of experimental setup for temperature measurements by OH-LIF ( Figure 2S) and a plot of simulated temperature profiles after changes in the kinetic modeling ( Figure 3S) (3), (4), (7), (9), (12), (14), (24), (43), (82) …”

“…1,2 In Brazil, ethanol is extensively used such as gasoline additive and commonly direct as an automotive fuel in a large part of the national fleet. 3,4 Nowadays, the use of ethanol has been increasing due to the "Flex fuel motors", in which the automotives vehicles can run on gasoline or ethanol fuels in any fraction. Recently, ethanol has also been applied as a pure fuel in small aircraft for aerial spraying in agriculture.…”