Effects of Grades and Other Loads on On-Road Emissions of Hydrocarbons and Carbon Monoxide

ABSTRACT

This project was developed to assess driving patterns that promote high emissions episodes, also known as emission excursions, particularly while driving on roads with grade. An instrumented vehicle was equipped to record driving conditions such as speed and grade, as well as measure emission rates of total hydrocarbons and carbon monoxide. Controlled runs with predetermined cruise speeds between 35 and 55 mph and accelerations less than 3.3 mph/second were conducted on flat terrain and on hills with grades ranging from 0 to 7%. The hills were located in metropolitan Los Angeles, both along freeways and arterial roads. For hydrocarbons, the increase in emissions was about 0.04 g/mile for each 1% grade increment. For carbon monoxide (CO), the increase was more dramatic: 3.0 g/mile for each 1% grade increment. For a fully occupied vehicle with four passengers on a 4.5% grade, emissions increased by 0.07 g/mile for hydrocarbons and 10.2 g/mile for CO. Air conditioning operation, at full setting, further increased emissions while driving on hills (4.5 and 6.7% grades) by 0.07 g/ mile for hydrocarbons and 31.9 g/mile for CO.