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Particulate matter, mainly its finer fraction, is among the main atmospheric pollutants present in an urban environment. The relationship between the increase in the concentration of this pollutant and the harm to human health is well established. The main sources of particulate matter in urban areas are mobile sources, which includes the exhaust emission from light duty vehicles. In Brazil since its advent in 2003, there has been great penetration in the market for bi-fuel or "flex" vehicles, which use ethanol, gasoline or their mixtures as fuel. More recently, with the introduction of public policies that led to the adoption of improvements in the energy efficiency of vehicles, the use of direct fuel injection technology (GDI), as a trend in downsizing for improved fuel economy, gained prominence. This technology optimizes the burning process in the combustion chamber of the engines, making their use more efficient.

It is common the development of greenhouse gas (GHG) emissions inventories, by private and public organizations. They are used as starting point for policy makers in their efforts on the mitigation of greenhouse gas emissions. It has already been established that vehicle emissions contain methane (CH4), whose formation is strongly dependent on the type of emission control system used. In the transportation sector, methane emission can contribute significantly to the total GHG emissions, considering the lifecycle of the fuel used. Although there are plenty of data about the regulated emission from vehicles, for greenhouse gases such data tend to be scarce. For this reason it is usual to try to establish ratios between the regulated pollutants and greenhouse gases so that the latter can be estimated from the available data of the former. The most usual way to do that is to make such estimation based on a relation between CH4 and NMVOC (non-methane volatile organic compounds).