ADULTERATION OF THE FUEL SOLD AT GAS STATIONS IN TWO TOWNS IN THE EASTERN AMAZON REGION OF NORTHERN BRAZIL

Purpose: The aimed witch of this study was to verify the quality of the fuel sold by gas stations in the Amazonian towns of Bragança and Tracuateua (Brazil). Method : It were applied physicochemical analyses to verify the anhydrous ethyl alcohol content of samples of gasoline, as well as the specific mass of samples of diesel and gasoline. Result and conclusion: Just over a quarter (26.47%) of the samples of gasoline collected in Bragança contained more ethanol than permitted by Brazilian law and were thus classified as in non-conformity. Three (75%) of the four gasoline samples from Tracuateua were non-conformity. In addition, 11.76% of the gasoline samples collected in Bragança were less dense at 20 °C than specified by the Brazilian legislation, and were thus considered as in non-conformity. Based on this same criterion, half (50%) of the gasoline samples collected in Tracuateua were also non-conformity. Diesel was the only fuel that presented no alteration in specific mass in either town. Research implications: There is a lack of academic studies related to this serious problem in the surveyed sites. This pioneering study is of great importance because it will alert local authorities about the problem of marketing fuels that do not meet the current specifications of the Brazilian legislation and whose emission of gases causes atmospheric pollution besides being harmful to life and to the environment. Originality/value: This study indicated that both types of gasoline (regular and premium) may be subject to adulteration in both Amazonian towns (Pará, Brazil).


INTRODUCTION
The quality of fuels is fundamentally important to guarantee public health and the integrity of the environment, given that the performance of internal combustion engines and their emission of pollutants are determined by the characteristics of the fuel they burn. The quality of a fuel is not easily determined, especially by visual inspection (Ahlin et al., 2021), and a number of cheaper substitutes can be used to adulterate the fuels sold by gas stations.
The adulteration of fuels by suppliers is a worldwide problem. It is an illicit practise that affects the quality of the fuel, with negative consequences for the productive chain and distribution network, the collection of taxes, the environment, and, ultimately, the final consumer (Santos et al., 2019). Fuel may be adulterated in a number of different ways, such as mixing lower octane gasoline with higher octane fuel, and the addition of kerosene to diesel or solvents to gasoline (Ahlin et al., 2021;Al-Ghouti et al., 2008). The fraud is difficult to detect when the adulteration involves the addition of hydrocarbons or other components that are normally present in the fuel (Vempatapu & Kanaujia, 2017;Takeshita et al., 2008;Moreira et al., 2003).
Adulterated fuels may increase the quantity of substances emitted by vehicles, including water vapor, and oxides of carbon (CO, CO2), nitrogen (NO, NO2), and sulfur (SO2), which are pollutants that may be harmful to both living organisms and the air (Gediky & Uzun, 2015, Canales-Gutierrez et al., 2022. Adulteration may also affect the performance and longevity of an engine, as well as the other components of an automobile (Felix et al., 2015;Ehsan et al., 2010).
In Korea, Ahlin et al. (2021) investigated the principal circumstances that led fuel retailers to commit fuel fraud. They verified a database of 1,083 cases registered between January 2010 and May 2015, and found that 70% involved the sale of adulterated fuel or the unauthorized recalibration of the fuel pumps. In developing countries, the adulteration of automotive fuels (gasoline and diesel) is a widespread practice (Vempatapu & Kanaujia, 2017;Kulathunga & Mahanama, 2013).
When the characteristics of a fuel are not consistent with the parameters established under the pertinent legislation, this fuel is considered to be contaminated, although this contamination is not always the result of adulteration. Adulteration involves the illegal, deliberate addition of substances that are cheaper than the fuel itself, with the purpose of obtaining financial advantages, which may range from tax evasion to price-cutting. This practise may not only damage engines, but also impact the environment (Santos et al., 2019).
The addition of ethanol to gasoline is potentially beneficial, given that ethanol is a highoctane fuel, and may potentialize the octane rating of the fuel. At high (adulterated) concentrations, however, it may result in an increase in the emission of CO (Vempatapu & Kanaujia, 2017).
The quality of a fuel is typically assessed by its distillation temperature and physical parameters, such as its density, color, pH, and ignition point (Ré-Poppi et al., 2009). The physicochemical properties of a fuel can be quantified using techniques such as Chromatography, Spectrometry, Infrared Spectroscopy, 1 H Nuclear Magnetic Resonance Spectroscopy, colorimetric techniques, and other electro-analytical approaches (Santos et al., 2019;Vempatapu & Kanaujia, 2017;Neto et al., 2014;Mendes & Barbeira, 2013;Pereira et al., 2013;Silva et al., 2012;Bueno & Paixão, 2011;Kaiser et al., 2010). Al-Ghouti et al. (2008) evaluated the adulteration of samples of gasoline based on their density, distillation temperature, and infrared analyses by the Fourier transformation (FTIR), together with analyses of multivariate calibration. Zhao et al. (2021) quantified and classified different commercial brands of gasoline using a combination of direct analysis, based on Real-Time Mass Spectrometry (DART-MS), and a Principal Components Analysis (PCA) of the different parameters, including the gasoline to methanol ratio, helium heating temperature, the sample movement velocity, and the pressure of helium gas.
Data from the statistical yearbook of the Brazilian Petroleum, Natural Gas, and Biofuels Agency (ANP, 2022) indicate that 42,401 retail fuel outlets were registered officially in Brazil at the end of 2021. Approximately 8.27% of these outlets (3,505 gas stations) are located in northern Brazil, that is, the Amazon region, with 1372 stations (3.24% of the total) in the state of Pará alone. These figures do not include clandestine outlets, which may have a major impact on the environment.
The addition of organic solvents (light and heavy aliphatic, and aromatic hydrocarbons) to gasoline is a practise observed frequently in Brazil (Wiedemann et al., 2005). Brazilian federal resolution number 807/2020 (ANP, 2020) establishes the specifications of automotive gasoline sold in the country, and the obligations of retailers in terms of quality control.
The quality of the gasoline sold by Brazilian retailers is verified routinely by physicochemical analyses, following ANP regulations. The gasoline is considered to be adulterated when a certain concentration of hydrocarbon solvents is added deliberated to the fuel for profit (Kaiser et al., 2010).
In the present study, gas stations in two Brazilian towns, in the northern state of Pará, were surveyed using physicochemical testing to evaluate the quality of the fuel sold by the outlets. The results of these tests were used to determine whether the fuel sold at the gas stations was being adulterated.
Five gas stations (I-V) were monitored in Bragança, where samples were collected in December 2018, and in April, June, and November 2019. Samples of all three types of fuel (regular and premium gasoline, and diesel) were collected in all months from all five localities except gas station I, which did not sell premium gasoline. Regular gasoline was not available at station II in April, premium fuel was not sold by station IV in June, and diesel was unavailable at station I in November. Two gas stations (P1 and P2) were surveyed in Tracuateua in November 2019, with a sample of each type of fuel being obtained from each locality except for diesel, which was not available at station P2. Two tests were applied to analyze the quality of the fuels sold by the gas stations in Bragança and Tracuateuathe anhydrous ethyl alcohol (anhydrous ethanol) content and specific mass tests: • The anhydrous ethanol content test (ANP, 2017) separates the ethanol from the gasoline to determine the content of anhydrous ethyl alcohol in the fuel. The amount of ethanol removed from the gasoline, and the content (percentage) is compared with the parameters established by Brazilian law (Brasil, 2015); • The density test is applied to samples of both gasoline and diesel to determine the specific mass of these fuels, for comparison with the parameters established under Brazilian law (ANP, 2013;ANP, 2020). Fuel densities incompatible with these parameters indicate the addition of substances that alter the content of the fuel illegally. The density test was conducted using a digital densimeter, which is employed to measure the relative or absolute density of a substance using an oscillator. The oscillator is a hollow, U-shaped tube, which is filled with the test liquid and agitated harmonically by an electronic mechanism, with natural changes in frequency. The density is corrected using a table of standard values to adjust the reading according to the ambient temperature.

Steps in the Anhydrous Ethanol Content Test
The anhydrous ethanol content test involves the following steps: • A 50-ml aliquot of the sample is placed in a 100 ml test tube. • Sodium chloride (25 gweighed on a semi-analytical balance) is transferred to a 100 ml beaker, to which 50 ml of distilled water is added. Once the salt is dissolved completely, the solution is transferred to the 100 ml test tube. • The test tube is capped and inverted at least 10 times, to avoid excessive agitation, resulting in the complete extraction of the ethanol to the aqueous phase. • The test tube is set aside for at least 15 minutes or until the complete separation of the two layers. • The percentage of anhydrous ethanol in the gasoline is calculated using the formula (Equation 1): Where V = the percentage of anhydrous ethyl alcohol in the gasoline, A = the increase in the aqueous layer.

Brazilian Legislation on the Anhydrous Ethyl Alcohol (Anhydrous Ethanol) Content of Gasoline
These analyses were run according to the NBR-13992 protocol of the Brazilian Association of Technical Norms (ABNT). The ethanol content of the gasoline sold by gas stations in Brazil is defined by the Environment Ministry, which was previously known as the Ministry of Agriculture, Livestock, and Logistics, through ordinance MAPA number 75, issued on March 5th 2015 (Brasil, 2015). This legislation fixes the ethyl alcohol content of gasoline at 27%, with a tolerable margin of 1%.

Legal Limits in Brazil for the Density of Regular and Premium Gasoline at 20 °C
The density (specific mass at 20 °C) of gasoline (regular and premium) established by Brazilian legislation (ANP, 2020) for is 715 kg/m³. The analyses of the specific mass at 20 °C of the gasoline and diesel samples were run following protocol NBR-14065 of the ABNT.

Legal Limits in Brazil for the Density of Diesel at 20 °C
The protocol for the density test of the samples of diesel is the same as that of the gasoline (ANP, 2013). The only difference is the standard density, which is 815-850 kg/m³ in the case of diesel fuel.

RESULTS AND DISCUSSIONS
Four of the samples of regular gasoline collected in Bragança (Table 1) had an ethanol content that exceeded the parameters established by the Brazilian legislation (26-28%), i.e., they were non-conformity. Two of the values, from station gas V in December 2018 and April 2019, were in fact below the minimum threshold, while the April 2019 sample from gas station IV and the November 2019 sample from locality I exceeded the upper threshold.
While sample P1 from Tracuateua was conformity (anhydrous ethyl alcohol content = 28%), sample P2 was non-conformity (30%) ( Table 1). This sample was thus considered to be adulterated. June 2019 was thus the only month in which the anhydrous ethyl alcohol content of all the samples of regular gasoline from Bragança was according to the legal specifications ( Figure  2). Overall, 78.9% of the samples of regular gasoline from Bragança satisfied the legal specifications, and were thus considered to be normal. While fewer samples of premium gasoline were collected during the present study, a larger number exceeded the parameters established by the Brazilian legislation (26-28%). In Bragança ( Table 2), five of the 15 samples collected were non-conformity, including samples from gas stations II (29% in December 2018), III (11% in December 2018, 30% in November 2019), and IV (39.3% in April, 29% in November 2019). Once again, it appears that all these samples were adulterated.
Both samples from Tracuateua were non-conformity (ethyl alcohol content: P1 = 29%; P2 = 30%) ( Table 2). In this case, then, all (100%) the samples were considered to be adulterated. Once again, June 2019 was the only month in which the ethyl alcohol content of all the samples of premium gasoline from Bragança was according to specifications (Figure 3). Overall, one-part (66.7%) of the samples of premium gasoline from Bragança satisfied the legal specifications, and were thus considered to be normal. Variations in the ethanol content of gasoline are one of the parameters that may affect the emission of gases by Otto-cycle engines (Ribeiro et al., 2018;Chen et al., 2011;Ghazikhani et al., 2013;Yao et al., 2013;Pereira & Pasa, 2005). Chen et al. (2011) concluded that the greater the quantity of ethanol in the air-fuel mix, the cleaner the firing, with the emissions of HC and CO being reduced significantly when the ethanol content exceeds 20%.
The gasoline-ethanol blend is used as one of the measures of air quality (Yao et al., 2013) and greenhouse gases. These authors also refer to a number of studies about the effects of this blend on the emission of air pollutants.
The density of three of the samples of regular gasoline from Bragança (Table 3) was below the minimum threshold established by the Brazilian legislation (715 kg/m³). These cases included the April 2019 sample from gas station I (712.5 kg/m³) and the November 2019 samples from gas stations II (707.5 kg/m³) and IV (711.9 kg/m³). All three samples were thus considered to have been adulterated.
While sample P1 from Tracuateua was conformity (specific mass = 737.9 kg/m 3 ), sample P2 was non-conformity (711.4 kg/m 3 ) (Table 3). Half (50%) of the samples were thus considered to be adulterated. In this analysis, all of the samples of regular gasoline from Bragança were considered to have been normal in December 2018 and June 2019 (Figure 4). Overall, 84.2% of the samples of regular gasoline from Bragança satisfied the legal specifications, and were thus considered to be normal. Only one of the samples of premium gasoline from Bragança was below the legal specific mass threshold (Table 4). This was the sample from gas station IV in November 2019 (712.0 kg/m³), which was considered to have been adulterated. None of the samples from any of the other months were non-conformity, and 93.33% of all the samples tested were considered to be conformity. At Tracuateua, while the sample from gas station P1 was normal (specific mass = 732.5 kg/m 3 ), sample P2 was non-conformity (711.4 kg/m 3 ) (Table 4). This means that, once again, half (50%) of the samples from this town were considered to be adulterated.
All the samples of diesel from both Bragança and Tracuateua were above the minimum specific mass threshold established by ANP resolution 50/2013 (Table 5). The anhydrous ethanol content test used in the present study has been applied successfully by other authors. Petri Jr. et al. (2022) used this test to analyze the quality of samples of regular gasoline collected from 15 gas stations in the Brazilian town of Lavras, in Minas Gerais state, in 2018, 2019 and 2020. In this study, initially 73.33% of the gas stations were out of specification, and, in 2020, 13.33% exceeded the permitted range, concluding that there was an improvement in the quality of gasoline over the three-year period. In the town of Picuí, in the Brazilian state of Paraiba, gasoline samples were analyzed from four gas stations. The results of these analyses indicated that the content of all the samples was within the parameters established by the current Brazilian legislation (Firmino & Ferreira, 2022).
In 2021, the Brazilian Petroleum, Natural Gas, and Biofuels Agency (ANP, 2022) collected 75,672 samples of fuel (28.09% hydrated ethanol, 37.01% regular gasoline, and 34.90% diesel) in Brazil, 0.1% more than in 2020. Overall, 2.65% of these samples presented some type of non-conformity. A total of 513 gasoline samples were non-conformity, which was due to the anhydrous ethanol content in almost half (48%) of the cases. In the case of diesel, 1336 samples were non-conformity.

FINAL CONSIDERATIONS
In the present study, in two towns in northeastern Pará (Brazil), the anhydrous ethyl alcohol content of 31.58% of gasoline (regular and premium) samples collected was nonconformity in accordance with the parameters established under Brazilian legislation. The nonconformity was recorded, in varying proportions, in all two towns. Overall, 26.47% of the samples collected in Bragança was non-conformity, and Tracuateua (75% of the samples).
In terms of the specific mass (density at 20 o C) of the gasoline samples, 15.79% was non-conformity. 11.76% of gasoline samples from Bragança were non-conformity according to the parameters established by the Brazilian legislation, while half (50%) of those from Tracuateua were also found to be below the minimum threshold for this parameter. Diesel was the only fuel found to be within specifications in all samples.
Overall, then, the content of samples of both regular and premium gasoline obtained from retail outlets in both towns exceeded the parameters established by the current Brazilian legislation.