On top of looming tougher pollution rules for sport utility vehicles and other popular vehicles, an environmental engineer here now has devised a new measurement that is likely to have a future impact on air pollution measures and standards nationwide.
It's called ppvm -- pollutant per vehicle mile -- and it measures the total particulate-matter emissions a vehicle makes per mile traveled.
Jay R. Turner, D.Sc., assistant professor of chemical engineering and civil engineering and director of the University's Air Quality Laboratory, has performed an ambitious study of vehicular emissions in the St. Louis region, measuring particles smaller than 2.5 micrometers in diameter.
Results from an urban interstate site and a nearby rural Illinois site that Turner surveyed indicate that an average urban vehicle, whether a motorcycle or diesel truck, emits between 30 and 40 milligrams of particulate matter per mile traveled; an average rural vehicle emits between 200 and 300 milligrams ppvm traveled.
So much for fresh country air.
"We think there is much more heavy diesel traffic outside the city, and there are greater road dust emissions in rural areas because of the proximity to open land, and those account for higher rural readings," Turner explained.
Road dust is more than the simple dirt a vehicle stirs up as it moves along the road. Besides dirt from soil, road dust also contains the suspended fine particulate matter created from tail pipe emissions. It is a major component of vehicular air pollution and a matter of serious concern to the U.S. Environmental Protection Agency (EPA) and the medical profession. Upper respiratory illnesses, cardiovascular diseases such as arrhythmia, and cancer increasingly are being linked to road dust and other vehicular particulate matter. The acidity of the matter, its heavy metal composition and the sheer volume of minuscule particles suspended in the air all make your automobile particulate-matter air pollution a potential public health threat.
Turner and his students used particulate matter samplers that pull air through filters, measuring the mass of the filters before and after the sampling. They concentrated on Interstate 40, which runs through the heart of St. Louis, and Interstate 55 in Madison County, Ill., some 30 miles northeast of St. Louis.
Periodically, from January to April 1998, the team painstakingly counted and classified vehicles at both sites during six- to eight-hour time spans, taking five-minute readings every 15 minutes while they collected the particulate-matter samples. They determined that the rural site averaged about 1,300 vehicles per hour; the urban location varied widely from 7,500 to 10,000 vehicles per hour.
The results of the study, which was funded in part by the EPA, were published in the Journal of Air and Waste Management Association. The data he has collected, plus his analysis of U.S. EPA mathematical models that predict air particulate-matter emission rates, will help environmental agencies and municipalities better sample their roads and address their particulate-matter air quality challenges.
"The numbers indicate that a single vehicle stirs up a considerable amount of particulate matter, more so than what people might think," Turner said. "When you then consider that you can multiply this daily value by the many thousands of miles vehicles travel on the roads each day, you get a clearer view of what role the automobile potentially plays in air pollution."
