What is Particle Pollution?
The term Particle Pollution or Particulate Matter (PM) includes both solid particles and liquid droplets found in air. Many man-made and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as "fine" particles. Sources of fine particles include all types of combustion (motor vehicles, power plants, wood burning, etc.) and some industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse". Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.

In 1997 the Environmental Protection Agency (EPA) proposed a new standard of ozone and particle pollution levels in the atmosphere. The concentration of particles of up to 10 microns in diameter(PM₁₀) at each monitor within an area must not exceed 150 µg/m3, in one hour more than once per year, averaged over 3 years. The concentration of particles up to 2.5 microns in diameter (PM_2.5), must not exceed 15 micrograms per cubic meter (µg/m3) and 35 µg/m3, respectively, each year and 24-hour period.

However, a coalition of business and industry interests sued to have those standards blocked, claiming they were too expensive and ill-conceived. In 1999 a federal court agreed, issuing a ruling blocking implementation of the tougher standards. Changes were made again in February 2001, when the U.S. Supreme Court unanimously upheld the constitutionality of the Clean Air Act as EPA had interpreted it in setting health-protective air quality standards for ground-level ozone and particles. The Supreme Court also reaffirmed EPA's long-standing interpretation that it must set these standards based solely on public health considerations without consideration of costs.

However, the Supreme Court did find that the EPA's plans for implementing the rules were unreasonable, and it ordered the agency to develop new implementation policies. Industry opponents immediately promised to use this aspect of the ruling as the basis for new legal challenges to weaken implementation of the new standards. It remains to be seen if the new standards will truly take effect as legislated.

According to the EPA, the new ozone and particle pollution standards will have the following effects:

Reduced risk of significant decreases in children's lung functions. The new standards should provide approximately 1 million fewer incidences of difficulty of breathing or shortness of breath in children each year. These problems can limit a healthy child's activities or result in increased medication use, or medical treatment for children with asthma.

Reduced risk of moderate to severe respiratory symptoms in children. The new standards should result in hundreds of thousands of fewer incidences each year of symptoms such as aggravated coughing and difficult or painful breathing.

Reduced risk of hospital admissions and emergency room visits for respiratory causes. The new standards should result in thousands fewer admissions and visits for individuals with asthma.

Reduced risks of more frequent childhood illnesses and more subtle effects such as repeated inflammation of the lung, impairment of the lung's natural defense mechanisms, increased susceptibility to respiratory infection, and irreversible changes in lung structure. Such risks can lead to chronic respiratory illnesses such emphysema and chronic bronchitis later in life and/or premature aging of the lungs.

Reduce the yield loss of major agricultural crops, such as soybeans and wheat, and commercial forests by almost $500,000,000.

What are the health effects from Particle Pollution?
The Environmental Protection Agency has found that numerous health effects arise from both fine and coarse particles when they accumulate in the respiratory system. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Health effects have been associated with exposures to PM over both short (such as a day) and longer periods (a year or more).

• When exposed to even small levels of PM, people with existing heart or lung diseases-such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease-are at increased risk of premature death and or admission to hospitals or emergency rooms.
  
• The elderly are very sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases.
  
• Children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath when exposed to levels of PM.
  
• PM can increase the susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.
  

What Parents Need to Know About Diesel School Buses:
If your kids are riding a diesel bus to school, chances are they're being exposed to unacceptable levels of particle pollution. Visit the Natural Resource Defense Council website for more information.

Recommended links:
EPA website on particle pollution.
American Lung Association website on particle pollution.

For detailed information about real-time pollution levels in the U.S., visit the Environmental Protection Agency's Website.