Evaluating the categorical effect of vehicle characteristics on exhaust emissions

The study assessed the categorical effect of vehicle age, frequency of maintenance and emission technology on vehicle emissions. Concentrations of carbon dioxide, hydrocarbons, carbon monoxide, and nitrogen oxide samples were taken from one thousand and two (1002) light-duty gasoline vehicles at three vehicle inspection centers in the city of Accra. Vehicle age was positively related to CO and HC emissions. The use of emission technology was negatively related to CO and HC emissions, but positively related to NO_x. Vehicle maintenance had a significant negative relationship with HC but no significant relationship with CO, CO₂, or NO_x. Categorically, moderate and over-aged vehicles were positively related to CO and HC with over-aged vehicles being more so. Furthermore, 2-way and 3-way converter were negatively related to exhaust emissions, but 2-way converter was positively related to NO_x. However, the coefficient value of the significant relationship between 3-way converter and CO (β = −0.374) as well as HC (β = −0.460) emissions was higher than 2-way converter. Regular maintenance of vehicles showed significant negative relations with HC, with insignificant relation with CO, CO₂ and NO_x emissions. The findings suggest that vehicle age, regular maintenance and use of emission technology are critical factors to consider when reducing vehicle emissions.