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Among the types used in Brazil is alcohol. “As it already has oxygen in its composition, its combustion is easier and, therefore, releases less pollutants”, says chemist Ernesto Gonzalez, from the University of São Paulo (USP). This does not mean, however, that it is harmless – in fact, all fuels release the following poisons into the air: carbon monoxide (CO), nitrous oxides (NO and NO2) and hydrocarbons (compounds of hydrogen and carbon). The most polluting of all is diesel. The fact that it is formed by long chains of carbon makes its combustion incomplete, making it release soot (that dangerous black smoke), in addition to nitrous oxides that cause lung problems. Worse: when the fuel is impure, burning produces sulfur dioxide (SO2), a gas that forms acid rain and irritates the respiratory system. Gasoline is also made up of carbon atoms, but in smaller chains than diesel.
Therefore, it pollutes less, but also releases CO – which causes nausea and decreases the oxygen transport capacity in the blood – and hydrocarbons, which can be carcinogenic agents. The alcohol engine has the advantage of releasing little CO and hydrocarbons. However, on average for new and used cars in circulation, gasoline rates are better. “That’s because, in the 1990s, the fleet of gasoline vehicles was modernized and incorporated technologies that reduce pollution. The ethanol fleet continues to age”, says engineer Manoel Paulo de Toledo, from the Environmental Sanitation Technology Company (Cetesb), in São Paulo.