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Particulate
Matter
Evidence from community
studies links particulate exposure to premature death, increased
hospitalization, school absence, and lost work days due to respiratory and
cardiovascular diseases like asthma.
Particulate matter, which includes solid
particles as well as liquid droplets found in the air, can be described as
"haze." Breathing particulate matter can cause serious health
problems. Particulates also reduce visibility in many parts of the U.S. They can
also accelerate corrosion of metals and damage paints and building materials
such as concrete and limestone.
Particulate matter comes from a variety of
sources. Some particles are emitted directly from their sources such as
smokestacks and cars. In other cases, gases such as sulfur oxide, SO2,
NOx, and VOC interact with other compounds in the air to form particulate
matter. As a result, the chemical and physical composition of particles varies
widely. "Coarse" particles are larger than 2.5 micrometers and
generally come from sources such as vehicles traveling on unpaved roads,
materials handling, crushing and grinding operations such as cement
manufacturing, and combustion sources. Particles less than 2.5 micrometers
(0.0004 inch) in diameter are known as "fine" particles. Fine
particles result from fuel combustion in motor vehicles, power plants and
industrial facilities, residential fireplaces, woodstoves, wildfires, and
prescribed forest burning. Fine particles can also be formed in the atmosphere
from gases such as SO2, NOX, and
VOC.
Health & Environmental Effects
Particulate matter less than 10
micrometers in size, including fine particles less than 2.5 micrometers, can
penetrate deep into the lungs. On a smoggy day, one can inhale millions of
particles in a single breath. Tens of millions of Americans live in areas that
exceed the national health standards for particulates. In recent studies,
exposure to particulate pollution - either alone or with other air pollutants
- has been linked with premature death, difficult breathing, aggravated
asthma, increased hospital admissions and emergency room visits, and increased
respiratory symptoms in children. People most at risk from exposure to fine
particulate matter are children, the elderly, and people with chronic
respiratory problems.
Fine particles scatter and absorb light,
creating a haze that limits our ability to see distant objects. Some
particles, such as sulfates and nitrates, grow in size as humidity in the air
increases, which increases the amount of haze and reduces visibility. Particle
plumes of smoke, dust, and/or colored gases that are released to the air can
generally be traced to local sources such as industrial facilities or
agricultural burning. Regional haze is produced by many widely dispersed
sources, reducing visibility over large areas that may include several states.
Regional Haze
Chemical reactions of air pollutants and
weather conditions can create fine particles, which can remain in the air for
several days and be transported great distances. As a result, fine particles
transported from urban and industrial areas may contribute significantly to
impaired visibility in places, such as national parks, valued for their scenic
views and recreational opportunities.
Sources of regional haze vary from
region to region. In the eastern U.S., for example, sulfates from power plants
and other large industrial sources play a major role. In the western U.S.,
nitrates, sulfates, organic matter, soot, and dust emitted by power plants,
motor vehicles, petroleum and chemical industrial facilities, wildfires, and
forest-management burning, all contribute to reduced visibility.
Visibility conditions vary across the
country. With a few exceptions, much of the eastern U.S. has poorer visibility
than the western U.S. because of higher levels of particles from manmade and
natural sources, as well as the effect of higher humidity levels on those
particles. Visibility in the eastern U.S. should naturally be about 90 miles,
but air pollutants have reduced this range from 14 to 24 miles. In the western
U.S., visual range should be approximately 140 miles, while current conditions
limit it to 33 to 90 miles. Visibility also varies seasonally and is generally
worse during the summer months, when humidity is higher and the air is
stagnant.
The Clean Air Act established special
goals for visibility in some national parks and wilderness areas. In 1994, EPA
began developing a regional haze program that is intended to ensure that
continued progress is made toward the national visibility goal of "no
manmade impairment." Such control efforts would likely result in improved
public health protection and visibility in areas outside national parks as
well.
Examples of regional strategies for
reducing fine particulate levels include:
- reducing particulate emissions by
conserving energy and promoting renewable energy sources like solar-
and wind-powered energy
- controlling SO2 emissions
from power plants and industrial sources
- reducing particulate emissions from
diesel truck and bus exhaust
- reducing controlled burning to manage
undergrowth in forested areas.
EPA's "regional haze"
program is intended to ensure continued progress is made toward the national
visibility goal of "no manmade impairment."
U.S. Environmental Protection Agency
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