Ozone Formation - Reactivity Emission Factors of Light Duty Vehicles Using Gasoline and Ethanol 2014-36-0252

The secondary pollutants formation in the atmosphere, such as ozone (O₃), comes from the reactions between volatile organic compounds (VOCs) and the photochemical oxidants in the presence of oxygen and nitrogen oxides (NO_x). The understanding of VOCs reactivity emitted by light duty vehicles is very important to construct reactivity scales regarding ozone formation.

In 2003, flex-fuel vehicles were released in the Brazilian market and nowadays, they represent over 50% of the total light duty vehicle fleet in the country. In 2007, new tailpipe emission limits were implemented for Non-Methane Hydrocarbons (NMHC), a group of pollutants included in VOCs. The new NMHC limit became a challenge to homologate some flex-fuel models, when fueled with ethanol. To deal with this issue, other legislation allowed the subtraction of the unburned ethanol emission from the NMHC value. In 2010, a local environmental agency published a study mentioning the need to revise this subtraction, since the unburned ethanol can also contributes to ozone formation. To better understand this issue, it was created, in 2012, a working group in Brazil, to discuss about vehicle exhaust gases reactivities to form ozone.

This paper presents theoretical concepts and a calculation methodology to estimate the potential reactivity of the VOCs to form ozone. It also includes emission experimental results for different vehicles using gasoline, ethanol and Compressed Natural Gas (CNG).