**1. Introduction**

The research field on alternative fuels has been developed in order to reduce the current dependence on petroleum derivatives and to improve air quality. Since the transportation sector represents one of the largest contributions to greenhouse gas (GHG) and other gas pollutants inventories, increasing the use of renewable fuel potentially reduces GHG emis‐ sions, such as carbon dioxide (CO2), which contribute to global warming and climate change [1, 2]. Brazil is an important scenario for the study of environmental impact from the largescale use of biofuels because a significant fraction of the vehicular fuels is derived from biomass (ethanol and biodiesel). In Brazil, anhydrous ethanol (maximum water mass content 0.7%) is added as an anti-knock additive to regular gasoline at a concentration ranging from 20% to 25% (known as gasohol or Gasoline C, E20, or E25 in Europe). Hydrous ethanol (maximum water concentration of 7.4%) is also used as a fuel in light-duty vehicles (LDV). Additionally, Brazil has experienced the use of biodiesel as additive to regular diesel since 2008. The minimum biodiesel content was set to 2% in 2008 and this content has been increasing, reaching 10% in 2015.

### **1.1. Bioethanol and biodiesel: The main biofuels in Brazil**

Ethanol biofuel has characteristics that favor cleaner combustion, therefore reducing the emission of air pollutants. Ethanol is produced from the fermentation of agricultural products

such as sugar cane, corn, wheat, beet, and cassava. The vast majority of ethanol produced worldwide is from sugar cane, mainly in Brazil [3]. Biodiesel consists of long-chain fatty acids esters mixture, which is produced by transesterification reaction of triglycerides present in vegetable oils or animal fats with short-chain alcohols in the presence of a catalyst (normally a base such as sodium (NaOH) or potassium (KOH) hydroxide) [4]. Figure 1 shows transes‐ terification reactions of triglycerides for biodiesel production. 23

Figure 1 Transesterification reaction of triglycerides for biodiesel production. **Figure 1.** Transesterification reaction of triglycerides for biodiesel production.

Biodiesel use has been stimulated as an environmentally favorable alternative, since many studies have shown that biodiesel blends reduce particulate matter (PM), carbon monoxide (CO), and total unburned hydrocarbon (THC) emissions compared to diesel fuel [1, 5-8]. Biodiesel blends have been shown to reduce the overall life cycle emissions of CO2, when evaluated using a total carbon life cycle analysis [1, 9], although this can depend on a variety of factors, such as land use change and transportation [10, 11]. A drawback in using biodiesel blends, however, is the potential to increase nitrogen oxide (NOx) emissions compared to ultralow sulfur diesel fuel [5-7, 9, 12].

The Brazilian specification for biofuel is similar to the European and American, with some flexibility to meet the characteristics of domestic raw materials. The Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) is the governmental agency that regulates fuels sold in Brazil through resolutions and technical specifications. The ANP resolution Nº 42 [13] provides a biodiesel specification (B100) according to the provisions contained in the Technical Regulation No. 4/2004. ANP Resolution Nº7 provides a specification for bioethanol (anhydrous and hydrous ethanol) according to the provisions contained in the Technical Regulation Nº 3/2011. Acceptable values or ranges for physical and chemical properties of both Brazilian biofuels, the respective analytical methods, and the importance of each analysis can be found on specialized literature [4, 14-16].

Biofuel analysis should be performed on a representative sample obtained according to the same methods described on ABNT NBR 14883 - Petroleum and petroleum products - Manual sampling or ASTM D 4057 - Practice for Sampling Petroleum and Liquid Petroleum Products (Practice for Manual Sampling of Petroleum and Petroleum Products) or ISO 5555 (Animal and vegetable fats and oils - Sampling). The monitoring of metals in bioethanol, such as iron and copper, is recommended by ANP as well as European and American norms, but not in biodiesel. Trace metals in biodiesel can catalyze oxidation processes which lead to the degradation of biodiesel and therefore this should be a parameter included in controlling parameters [15]. Inorganic anions such as chloride and sulfate in bioethanol can induce corrosion inside engine and storage tanks. Additionally, the monitoring of residual glycerol in biodiesel is related to the possible formation of acrolein, a pollutant known to cause severe adverse human health effects, from the burning of biodiesel containing glycerol. Glycerol is the main co-product formed during the production of biodiesel (Figure 1). Other impurities can be found in biodiesel such as residual alcohol, catalysts, and free fatty acids [17, 18].

Fuel quality, improvements in the technology applied to the engine, and the maintenance conditions are the main factors that influence the issuance of vehicle pollutants. To reduce emissions considerably, it is necessary to develop advanced combustion technologies and control devices, as well as environmentally clean fuels (with low pollution potential). Although many efforts have been done to develop environmentally friendly technologies and "clean fuels" to reduce environment pollution, vehicular emissions are still the main pollution source in many countries due to the increase in the urbanization and in the necessity of daily increase of displacements. Therefore, the development of public policies to reduce the contribution from this sector to air pollution becomes the priority for several urban areas. In the following, the historic overview of Brazilian biofuel uses and public programs of vehicular emissions control are addressed.
