-
 |
Washtenaw County has been designated by EPA as “out of attainment” with the PM2.5 National Ambient Air Quality Standard. High levels of particulate matter are associated with human health concerns.
Source: Michigan Department of Environmental Quality (pdf)
Last updated: July 2009 |
What is particulate matter?
"Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. ( EPA)
How does particulate matter affect the environment?
Particulate matter is strongly linked to human health concerns. The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. EPA groups particle pollution into two categories:
- "Inhalable coarse particles," such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.
- "Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.
Most particulates come from sources other than vehicles, however diesel particulates have some of the highest health impacts. One important strategy is to reduce the number of diesel buses or ensure that the diesel buses remaining have the latest catalyzed particulate filters on them. Because of the close proximity of buses to people, they have disproportionate heath impacts. Hybrid buses also are a significant improvement , even without particulate traps, because they reduce the load on the diesel engine during acceleration when particulate emissions are the highest. Another effective strategy is to retrofit existing diesel engines with particulate traps. This is very effective, but also very expensive. California has a lot of experience with this. Simply requiring exhaust stacks on diesel vehicles helps a great deal in reducing exposure to the emissions, because the stacks elevate the emissions above ground level.
Gasoline engines do not emit much particulates, except under two conditions. One is a malfunctioning vehicle - especially one that is burning oil - and the other is during cold starts. Gasoline engines do emit significant particulate emission when they are running with a rich air/fuel ratio, which occurs during warmup (especially at colder temperatures) and with many malfunctions. An I/M program would help with malfunctions (but is extremely unpopular) and block heaters would help with cold start emissions.
More information
|
-
Find out how YOU can help improve the State of Our Environment.
|
|
