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Particulate Matter
What is Particulate
Matter?
Health
and Environmental Effects
How Big Are These Particles?
What
is EPA Doing about Particulate Matter?
Opacity
Thick, black smoke belching out of the exhaust pipes of trucks. White smoke that comes from burning leaves or burning wood in the fireplace. A hazy brown layer in the morning sky. Visible material (other than steam) puffing out of smoke stacks. Swirls of dust stirred up by a car on a dirt road. These are all examples of particulate matter.
Particulate matter arises both from direct emissions from many types of sources and from atmospheric reactions of gaseous pollutants. The examples above are direct emission sources. Particles originating from atmospheric reactions arise from the same process as acid rain. As the most important examples, sulfur dioxide and nitrogen oxides are emitted into the atmosphere, where they undergo chemical reactions that result in formation of sulfate and nitrate particles.
Particles generated by stirring up dust or by crushing or grinding operations tend to consist of more large particles than small particles. Particles generated by combustion and high temperature metallurgy are predominantly small particles. Particles that originate from atmospheric reactions are generally very small. Consequently, particles from combustion, from metallurgy, and from atmospheric reactions generally have greater health impacts than particles from stirred up dust.
Health and Environmental Effects
Numerous recent studies have shown that airborne particles (either solid or liquid) cause serious health problems. EPA has estimated that airborne particles cause over 15,000 premature deaths in the United States per year. Scientists have correlated exposure to airborne particles with increased hospitalizations for asthma attacks, worsening of lung disease, chronic bronchitis, and heart damage. A March 2002 study suggests furthermore that airborne particles can cause lung cancer. In addition to these human health effects, particulate matter is the main cause of haze which decreases visibility. Particulate is eventually settles on land or water which can acidify lakes, deplete the nutrients in soil, and damage sensitive forests and crops.
Particulate matter is present in many different sizes. The smaller the particle, the more dangerous, because it can travel deeper into the lungs.
Particulate matter comes in a range of sizes. Particles that remain airborne are generally below a nominal aerodynamic diameter of about 75 micrometers (μm). Some particles are as small as large molecules, below 0.1 μm. However, particles in the upper end of this size range are mostly trapped in the nose or upper respiratory system. More serious health effects result from breathing particles below 10 μm, especially from particulate matter below 2.5 μm in size. Particulate matter of 10 μm and smaller is called PM10 and particulate matter of 2.5 μm and under is known as PM2.5 or fine particle.
How long is a micrometer? A micrometer is one millionth
of a meter. A micrometer is sometimes also called a micron. This
small distance translates to about 1/25000 of an inch. Common comparisons
are to an average human hair, which is about 70 μm. So, a 10 μm
particle would thus be about 1/7 the diameter of an average human hair,
and a 2.5 μm particle would be about 1/30 the diameter of an average
human hair.
"Nominal aerodynamic diameter" refers to a favored choice of various
ways of defining size for real world particles with irregular shapes and various
densities. A particle with a nominal aerodynamic diameter of 2.5 μm
is a particle that has the same aerodynamic characteristics as a spherical
particle with a 2.5 μm diameter with a density equal to that of water. Thus
it would similarly penetrate deep into a lung. EPA is interested in how
deeply a particle penetrates into the lung, using the nominal aerodynamic diameter
is our method of assessing size of non-spherical particles. A particle's
nominal aerodynamic diameter is generally similar to its conventional, nominal
physical diameter.
What Is EPA Doing about Particulate Matter?
EPA has set the
following primary (health-related) and secondary (welfare-related) National
Ambient Air Quality Standards (NAAQS) for particulate matter:
| PM 2.5 (particles
with diameters of 2.5 micrometers or less . annual arithmetic mean of 15 µg/m3 . 24-hour average of 65 µg/m3 |
PM 10 (particles
with diameters of 10 micrometers or less) • annual arithmetic mean of 50 µg/m3 • 24-hour average of 150 µg/m3 |
The particulate matter NAAQS are currently under periodic review. EPA uses the results of the latest studies on the health and welfareeffects of fine particulate pollution to determine if the standards should be revised or if additional standards are needed. Proposed revisions to the PM2.5 standard, PM10 standard, and a new course particulate standard were issued on December 20, 2005. The particulate matter regulatory action web site has the latest information on the proposed revisions.
EPA designated areas for PM2.5 on December 17, 2004. The 15 non-attainment areas in Region 5 encompass 63 counties in 4 states. A list and map of the current non-attainment areas can be found on EPA's Green Book website. The states are being required to take action to reduce the emissions causing excessive fine particulate concentrations. EPA and the states will evaluate the types of sources that contribute most significantly to the problem and can be most readily controlled. The states will also be required to establish emission limits for sources and engage in other programs to reduce emissions sufficient to remedy the violations.
There are no PM10 non-attainment areas in Region 5 now. EPA
evaluates revisions to PM10 limits so that areas will remain in attainment
of the PM10 standards.
EPA is also taking action itself to reduce emissions. EPA is administering
the acid rain program that Congress enacted as part of the Clean Air Act
Amendments of 1990. Despite the significant reductions in emissions
that have occurred over the last 30 years, we now know that more needs to
be done to protect the public health from the effects of particulate matter. EPA
has issued the Clean Air Interstate Rule which will cut sulfur dioxide and
nitrogen oxide emissions from power plants. New clean diesel rules
will dramatically reduce fine particulate emissions from heavy trucks and
other diesel powered equipment. The Clean Air Visibility Rule will
reduce haze in National Parks and other pristine areas by limiting PM2.5
emissions along with PM2.5 precursors such as sulfur dioxide and nitrogen
oxides.
Click here for a discussion of the role of opacity in EPA's particulate matter program, especially in enforcing compliance with emission limitations.