Air pollution caused by vehicle emissions has long been a concern in our society. Each year, the number of ozone alerts increases, indicating the quality of our air continues to decline due in part to the emissions of automobiles.
Dr. Chris Frey uses a first-of-its-kind instrument to measure automobile emissions in real-traffic conditions. The data he gathers will help determine how traffic patterns influence pollution.
At NC State, researchers are working to find ways to reduce automobile emissions. Using a newly developed machine, engineers are analyzing emissions produced by a variety of gasoline-powered automobiles. Dr. Christopher Frey, associate professor of civil engineering, and Dr. Nagui M. Rouphail, professor of civil engineering, and their team of researchers will use the information collected by the instrument to create computer models that show the effects of driving patterns and traffic signals on automobile emissions.
"We are the first to use this particular instrument for research. As a matter of fact, this is the first instrument of its kind," says Frey. "It offers an easily portable, on-board analysis of what air pollutants a vehicle is actually producing during operation."
The instrument, developed by CleanAir Technologies International Inc., offers low-cost, portable emissions analysis. NC State received the first machine produced, and the research team has worked with the company to refine and modify the instrument.
The unique ability to measure the actual emissions produced by a particular vehicle during start up and driving allows Frey and Rouphail to use real-world data instead of the generalizations based on laboratory-produced data currently used to predict emissions.
"What makes this instrument perfect for this research is that it can be set up easily in any vehicle," says Frey. "In the past, these analysis instruments for on-board testing were expensive and bulky."
While the team has only been testing vehicles for a few months (the instrument arrived on campus in early July), the data collected is already producing new information about what causes high emissions. Some of the results have been surprising.
"A common belief based on laboratory emissions data is that idling produces high emissions," says Frey. "However, based on what we have collected so far, idle emissions are much lower than expected. Acceleration is the dominant producer of high emissions, indicating that changing traffic patterns to allow fewer stops with longer delays may reduce emissions."
Although it is commonly believed that high speed driving can produce very high emissions, results from the research team's measurements so far indicate that high speed emissions can be relatively low as long as driving is at a constant speed and on a level road. On the other hand, emissions can increase substantially when changing speeds to make lane changes or when accelerating rapidly to high speed.
The team is working with officials from the North Carolina Department of Transportation to better understand the relationship between traffic signal timing and emissions. The team is conducting on-road measurements before and after traffic signal timing is changed on a number of corridors in the Research Triangle region. The results of this project will provide a basis for predicting the effect of new traffic signal timing on vehicle emissions during real-world driving. The researchers hope that improving the timing of traffic signals can have a significant effect on pollution in high traffic areas.
The team will also create a list of driving habits that can be modified to reduce emissions. The driving tips will be posted on their Web site, www4.ncsu.edu/~frey/emissions/ .
Photos by Roger Winstead
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