When it comes to air quality in major cities, the main villain is the fleet of automotive vehicles which release millions of tons of pollutants into the atmosphere every day. Among the main and best-known ones are carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), the hydrocarbons and particulate material, such as dust and smoke. These pollutants are regulated and there are precise limits for their emission by engines, right from when they are made, according to Proconve, the Control Program against Automotive Vehicle Air Pollution, launched by the federal government in 1986. However, vehicle exhaust systems release other pollutants, including the so-called polycyclic aromatic hydrocarbons, or PAHs, which are neither systematically controlled nor covered by environmental legislation. A recent study conducted at the School of Public Health of the University of Sao Paulo (FSP-USP) showed that these gases are found in the atmosphere in large amounts. The good news is that cars running on alcohol can reduce this problem by 92% as compared to cars running on gas.
“These substances are carcinogenic and must be equally controlled,” states chemical engineer and sanitation specialist João Vicente de Assunção, a professor and head of the FSP-USP Environmental Health Department, who coordinated the project that quantified the concentration of PAHs and other unregulated toxic pollutants in the city of Sao Paulo. The PAHs are a vast group of organic compounds whose main feature is that they have two or more aromatic rings in the chemical composition of their molecules. These rings consist of six carbon atoms and six hydrogen atoms; the main representative of this class of chemicals is benzene. Among the dozens of PAHs that exist, 16 are more important because they harm health: naphthalene, fluorene, phenanthrene and, most toxic of all, benzopyrene.
Besides being emitted by automobiles, PAHs are released when garbage is incinerated, in cigarette smoke and in the burning of coal or charcoal. “The problem with these compounds, as well as with the other ones that we have studied, such as dioxins and furans, is that they are highly toxic and generally soluble in fat. This means that several of them can accumulate in body fat. After they are fully metabolized in the organism and as the years go by, they can cause cancer, in particular of the lung and of the bladder,” explains Assunção.
Studies conducted by the researcher and his group followed three different lines. In the first, the objective was to analyze the concentration of PAHs in Sao Paulo air. In the second, the aim was to quantify the release of these compounds by alcohol or gasoline vehicles; and in the third one, the object of study was the emissions of diesel engines. To check the quality of Sao Paulo air, collection stations were set up at three points of the city: at the School of Public Health itself, in the district of Cerqueira Cesar, in the central part of the city; on the Marginal do Tiete beltway (in the district of Lapa, Western part of the city); and near Congonhas airport, in the South of the state capital. The air samples were collected in quartz microfiber filters and in polyurethane foam, from which they were subsequently extracted and analyzed with a mass spectrometer and a gas chromatograph. “The research showed that the concentration of benzopyrene in Sao Paulo is, on average, 1.09 nanograms per cubic meter of air. This is high when compared to European and American cities. It equals, for instance, four times the reference level of the United Kingdom, which is 0.25 nanograms per cubic meter, but the ideal is that it should only be found in the smallest possible concentrations, because even then it is still a health risk,” highlights Assunção.
The study of the emission of PAHs by vehicles was coordinated by the mechanical technologist Rui de Abrantes, who did his PhD at the USP School of Public Health and currently works for Cetesb, the Environmental Sanitation Technology Company. In these tests, conducted at Cetesb’s Vehicle Testing Laboratory, two types of cars, one with a flex-fuel or biofuel engine, running only on alcohol, and another with a gasoline-fuelled car. “For the vehicles to be representative of the São Paulo city fleet, we chose vehicles with 1.6 cc engines, with electronic injection and a catalyst,” Abrantes tells us. The gasoline car, a 1998 model, had done 67 thousand km, whereas the flex-fuel one, a 2004 model, had done 56 thousand km.
All in all, 15 different trials were carried out with these vehicles, 9 on the gasoline car and 6 on the flex-fuel one, with some parameters varying, such as the type of gasoline (regular, premium or adulterated), the type of engine oil (mineral or synthetic), alcohol quality (normal or adulterated), and whether or not there were additives – offered at gas stations – in the fuel. The gases were collected directly from the cars’ exhaust systems, simulating running conditions in an urban setting in the laboratory. “Once the analyses had been processed, we discovered that, on average, the alcohol cars emit 92% less PAHs than the gasoline ones,” says Abrantes.
The results also showed that using additives in gasoline cars causes an increase in the emission of naphthalene and phenanthrene, whereas in the cars tested with adulterated gasoline, with rubber solvents added, these two compounds were reduced. “Adulterated fuel uses rubber solvents that end up diluting the gasoline. If, on one hand, it emits fewer PAHs, on the other it may be releasing other unquantified toxic pollutants,” explains Abrantes. The use of synthetic rather than mineral oil, in gasoline vehicles, in turn, significantly contributes to reducing the emission of naphthalene and fluorene. Regarding ethanol-fuelled cars, the same types of oil were tested, but there were no statistically significant differences in the emission of PAHs. The study’s results were published in the January issue of the journal Atmospheric Environment.
Abrantes, from Cetesb, says that the law does not directly control the PAHs emitted by automotive vehicles because the tests required to detect these pollutants are expensive and would ultimately make cars more expensive. “As the PAHs are a hydrocarbon subgroup and are also found in particulate material, which are regulated pollutants, we can say that there is a measure of control over them, albeit indirect.”
The third front of the study – quantification of the emission of PAHs by diesel engines – was carried out in the lab of a manufacturer of such engines, taking into account the various PAH compounds. On average, the engines emitted 0.689 micrograms of benzopyrene equivalent toxicity per kilometer run. Because it is regarded as the most toxic of PAHs, benzopyrene is used as the yardstick for measuring the toxicity of these compounds: a factor 1 is ascribed to it, whereas the other ones have lower values.
Regarding gasoline cars, this index stood at 0.832 whereas in the ethanol cars, it was 0.016. However, one cannot make a direct comparison with the emissions of diesel engines, because the trial procedures are different. Additionally, the diesel engines tested were new, and therefore with lower PAH emissions, whereas the gasoline and alcohol vehicles belong to the fleet that is currently in use.
Chlorine and bromine
Besides investigating the emission of PAHs, Assunção and his collaborators also studied another two sets of toxic compounds released by vehicles, but overlooked by environmental legislation: the dioxins and furans. Both are organic compounds characterized by the presence of chlorine or bromine atoms in their composition. “We didn’t reach a definitive conclusion about the level of emissions of chlorinated furans and dioxins in diesel vehicles; but everything seems to indicate that it is just as significant, or even more so, than the emission in gasoline and alcohol cars,” he stresses.
The results of this research, which was financed by FAPESP, were presented in 2008 at the 28th International Conference on Persistent Organic Pollutants (POPs) (Dioxin 2008), in England, at the 16th International Conference on Modeling, Monitoring and Managing Air Pollution (Air Pollution 2008), in Greece, and at the 2007 meeting of the Inter-American Sanitation and Environmental Engineering Association, in Chile. “The United States, Japan and Europe have control programs and have been successful in reducing these three groups of substances (PAHs, dioxins and furans). We hope that our work will influence public policies that can lead to preventing and controlling these pollutants, which are so bad for human health,” stresses Assunção.
1. Characterization of dioxins, furans and polycyclic aromatic hydrocarbons in vehicle emissions and in an urban atmosphere(nº 04/02623-6); Type Regular Research Awards; Coordinator João Vicente de Assunção – USP; Investment R$ 213,044.00 and US$ 74,892.00 (FAPESP)
2. Study of the presence of dioxins and furans in the particulate material emitted by diesel engines (nº 02/00012-4); Type Regular Research Awards; Coordinator João Vicente de Assunção – USP; Investment R$ 13,557.71 (FAPESP)
ABRANTES, R. et al. Emission of polycyclic aromatic hydrocarbons from gasohol and ethanol vehicles. Atmospheric Environment. v. 43, p. 648-654, jan. 2009.