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1. Should wildfires be stopped altogether to protect our forests, our air, and our health? 2. What is the Clean Air Act? 3. What are the epa and mpca doing about pm?1. What do “pm” and “pm.” mean? 2. Which of these particles are the most harmful?
3. How do fine particles cause health effects? 4. What groups are most vulnerable to fine particle air pollution?

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On a Clear Day You Can See Forever
David W. Kelley
Department of Geography
University of St. Thomas
Rebecca Helgesen
Minnesota Pollution Control Agency
Figure 1a. On a bright March  morning
with an Air Quality Index (AQI) reading of ,
downtown St. Paul and the Minneapolis skyline
are clear. Photo: mpca staff
Figure 1b. On a hot June  day with an AQI
of , a haze dims the St. Paul landscape and
Minneapolis disappears. Photo: mpca staff
Part I—It’s a Small, Small World
December , , dawned clear and cold in London, England. The air was damp and stagnant. Heavy
black smoke rose from chimneys as Londoners lit the coal they burned to cook and heat their homes. Fog
began to roll in. By dusk, the smoke-filled fog had turned an impenetrable yellowish black.
By the time the smoky fog lifted four days later, , Londoners were dead of heart and lung complications.
Another , died during the following two weeks, as the persistent health impacts of the five-day fog
continued. When researchers compiled statistics, they estimated that during the next two months, ,
more died of causes directly related to that deadly fog.
The culprit in London’s killer fog wasn’t the fog itself. It was thousands of tons of tiny particles that clung
to the stagnant fog and filled residents’ lungs. Thick soot from the city’s coal-burning home hearths, diesel
buses, and factories hung near the ground, trapped by a slow-moving temperature inversion. Black smoke
concentrations measured during those five days reached more than  times normal levels.
For hundreds of years, Londoners have experienced discomfort related to particles in smoky fog (dubbed
smog in ). Recently, it has become clear that those fine particles are more than uncomfortable.
The most serious effects of small particles are associated with aggravation of heart or lung disease. Numerous
studies have related particles in the air to increased hospital admissions, emergency room visits, and
mortality. Aggravation of lung diseases, including asthma attacks and acute bronchitis, has been correlated
with short-term exposure. In people with heart disease, particles have been linked to heart attacks and
irregular heart rhythms.
According to Dr. Joel Schwartz of the Harvard School of Public Health, it’s not a small problem. By one
estimate, , people in the U.S., primarily older adults, die prematurely each year when fine particle
pollution increases to unhealthy levels. “This,” says Schwartz, “is larger than the death rate from breast and
prostate cancer combined.”
Minnesota is a long way from the London of the s—or even the troubled cities of the industrial
northeast United States. It has its own unique problems with smoke-related pollution, however, as
documented in the following article.
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 1
The material on this page is excerpted from “Out of a Clear Blue Sky: Regional Haze Mars Scenic Vistas, Even in
Minnesota” by Ralph Pribble, Minnesota Environment, Summer 2003, Vol. 3(3), p. 10.
Air pollution affects not only urban areas, but
national parks and wilderness areas as well. On bad
days, “regional haze” cloaks some of the United
States’ most treasured “purple mountain majesties”
in brown or white gauze. Many of the  million
Americans who each year visit parks such as the
Grand Canyon or Glacier National Parks are
surprised to find they can’t get a clear view of the
scenic wonders they have come to see.
The cause might surprise outdoor enthusiasts. It
is fine particles similar to those that blight our
urban skies. Some haze is natural, part of prevailing
climate dynamics. After all, the Great Smoky
Mountains were known by that name long before
the mid-South industrialized. Dust, organic
compounds, smoke from forest fires, and humidity
figure into what is considered natural (unpolluted)
Figure 2. A Forest Service improve automated
monitoring station just outside the bwcaw shows
the distinct difference between a clear day (more
than  miles visibility, above) and a hazy one
(less than thirty, below). Photos: usda Forest
In pre-settlement days, the farthest a person could
expect to see on a clear day was between  to 
miles in the Western U.S., and  and  miles in
the East. Today, however, typical visual range in the
West is  to  miles. In the East, it’s only  to
 miles. The culprit in this deterioration appears
to be human activities.
In , the U.S. Environmental Protection
Agency (epa) issued regulations designed to further
reduce haze and protect visibility, as well as specific
programs to reduce particle air pollution overall.
For example, the U.S. Department of Agriculture
National Forest Service’s improve (Interagency Monitoring of Protected Visual Environments) network
collects air samples and provides monitoring data on visibility and fine particulates at  Class I locations,
including Voyageurs National Park and the Boundary Waters Canoe Area Wilderness (bwcaw), both located
in northern Minnesota.
The equipment at improve sites includes automated samplers to measure airborne particles and particle mass,
along with light-monitoring equipment and a camera. According to Trent Wickman of the Forest Service’s
Duluth office, “The contributions of pollutants at the [bwcaw] are clear. A large portion is ammonium
sulfates, which are pretty clearly tied to coal combustion.” He added there’s not sufficient data yet to provide
trend analysis, but that “we’re getting to that point.”
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 2
Regardless of their source, trying to describe fine particles is like trying to describe animals to someone from
another planet. Just as animals can be large or small, feathered or furred, dangerous or benign, particles can
be varying sizes, solid pieces or liquid droplets, man-made or natural, dangerous or benign.
Some particles are emitted directly into the air, and some form in the air from chemical reactions of nitrogen
oxides, sulfur oxides, volatile organic compounds, and ammonia. Particles can cling to moisture droplets
or simply drift in the air. Scientists call particles “particulate matter,” abbreviated pm. Regulators generally
divide particulate matter into two categories on the basis of size: pm and pm..
1. What do “pm” and “pm.” mean?
2. Which of these particles are the most harmful?
3. How do fine particles cause health effects?
4. What groups are most vulnerable to fine particle air pollution?
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 3
Part II—Life’s Better at the Cabin
Particles are both urban and rural
Fine particle pollution is everywhere, as are the
combustion processes that create them. There is
no way to avoid it. The smokestacks and tailpipes
of cities and towns produce a large part of pm, but
sources exist in rural areas as well. Fine particles can
ride the wind to locations thousands of miles from
the original sources and stay in the air for a long
Even rural areas, including remote national parks,
are plagued by “regional haze,” a benign-sounding
term for fine particle pollution that has blown
in from elsewhere and obscures famous views. If
tourists at Arizona’s Grand Canyon, South Dakota’s
Badlands, and Tennessee’s Great Smoky Mountains
pick the wrong day to visit, they find the dramatic
scenery veiled by a gauzy haze. Although not as
badly affected as other areas, Minnesota’s Voyageurs
National Park also shows signs of regional haze.
Figure 3. Measurements based on one year of
monitoring at urban Minnesota sites.
One goal of the Clean Air Act is to restore the view of these national treasures to the clarity that onlookers
enjoyed before the advent of man-made air pollution. Class I areas, as defined in the Act, are  national
parks, monuments, and wilderness areas in the United States. Even remote, far-north Class I areas such as
Voyageurs and the bwcaw become hazy from transport of fine particles high in the atmosphere, where they
can be carried long distances.
Short-term exposure is enough
London’s  fog carried very high concentrations of fine particles. But can fine particles at elevated levels
really do so much damage so quickly? Recent research suggests that they can. Measurable changes in the
body may take place within hours of increased exposure, particularly in people with existing cardiovascular
or respiratory conditions.
The Health Effects Institute, an institution jointly funded by the epa and industry, commissioned a
nationwide study in the late s on the short-term effects of air pollution, the National Morbidity,
Mortality and Air Pollution Study (nmmaps). The study found strong evidence linking daily increases
in particle pollution to increases in mortality in the 90 largest U.S. cities (including the Twin Cities),
particularly from heart and lung diseases.
Re-analysis of the study due to a statistical problem did not change the basic conclusions:
• There is an association between short-term increases in particles and death, as well as hospital
admissions for heart diseases and chronic obstructive pulmonary disease.
• This association is strongest for respiratory and cardiovascular causes of death.
• The association was not attributed to other air pollutants.
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 4
Over  years ago, researchers at the Harvard School of Public Health released the results of a study
following , adults in six cities during a dozen years (Dockery et al., ). They found that people in
the city with the highest fine particle pollution had a  percent higher risk of death due to cardiopulmonary
causes than the residents of the least-polluted city.
Another study supports the Harvard findings. In the March th 2002 issue of the Journal of the American
Medical Association, Dr. George Thurston of the New York University School of Medicine and Brigham
Young University researcher C. Arden Pope reported on their landmark study that followed a half million
people in  U.S. cities for  years (Pope et al., ). Comparing health data to air pollution records,
they found that populations with prolonged exposure to particulate air pollution had significantly higher risk
of dying of lung cancer and other lung or heart diseases.
“Long-term exposure to air filled with fine particles carries almost the same risk of lung cancer and heart
disease as breathing secondhand smoke over a long period,” says Thurston. This wasn’t his only finding after
years of pm research.
“We also found that, if you are aged  and older, you have a considerably increased risk of having a heart
attack within two hours of a high fine particle episode,” says Thurston. “That risk doubles if you already have
heart or respiratory disease.”
But it isn’t only older adults who are at risk, says Thurston. He believes that babies from one month to one
year are also more at risk, for three reasons: they breathe more air per pound of weight; they tend to have a
high rate of respiratory ailments already, which leaves them more vulnerable; and they are developing rapidly.
As science zooms in on fine particles, we will learn more about their effect on us. But don’t expect the news
to get better. “Basically,” says Thurston, “everyone is at risk from air pollution—it’s just a question of how
The following material is excerpted from “Where There’s Smoke, There’s Smoke-Related Pollution” by Anne Perry
Moore, Minnesota Environment, Summer 2003, Vol. 3(3), pp. 7–9.
When wildfires burn, the smoke stops here
Smokey the Bear never said it would be like this. Kids of all ages know they are responsible for preventing
forest fires. What they may not know is that fire-related air pollution can have health consequences—for
people living both nearby and thousands of miles away.
Wind sent smoke from the  Colorado, Arizona, and Canadian mega-fires across whole states. The
blowdown area in the bwcaw remains a tinderbox. In the spring of , grass fires in Minnesota raced
across many communities, clouding the air with smoke. As summer heat and storms escalate, we can learn
what to do if weather conditions send harmful wildfire smoke in our direction.
Smoke gets in your eyes
Ninety percent of wildfire-related emissions are carbon dioxide (a major contributor to global climate
change) and water vapor. The rest includes particles in a range of sizes. Fine particles remain suspended in
the air from a few seconds to several months.
To help the general public and high-risk groups identify and reduce potential health problems related to
wildfires and smoke exposure, experts in several western state agencies offer easy-to-understand, visibilitybased guidance. (See an example at the Oregon Department of Environmental Quality at
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 5
wildfire-health.htm#using%20visibility.) The
bottom line: The more visible the smoke, the more
likely the health concern.
Though these visibility guides were developed for
local use, they apply far from active fires as well.
Air emissions travel: Airborne arsenic from Beijing
smelters turns up in Hawaii, U.S. factory pollutants
land in Europe, Saharan Desert dust falls in the
Caribbean. Wildfire pollution has the same airborne
transmission potential.
For example, during the - El Niño, smoke
from drought-related forest fires sent hundreds of
Malaysians, Indonesians, and Brazilians to local
clinics with respiratory complaints. The larger the
population downwind from any big fire, the greater
number of people potentially exposed.
Figure 4. During the summer of , powerful
storms ripped through the Boundary Waters Canoe
Area Wilderness, damaging nearly , acres of
timberland. Controlled burns will be used to lessen
the possibility of a massive fire. Photos: Superior
National Forest
The statistics are staggering. Each year forest fires
worldwide emit an estimated:
•  million tons of carbon dioxide
•  million tons of carbon monoxide
• . million tons of nitrogen oxides (a precursor
of ground-level ozone)
• particulate matter
• hydrocarbons (such as benzene)
• aldehydes (such as formaldehyde)
• trace minerals
In the United States, according to the National Interagency Fire Center
(, an estimated . million acres of wild land burned in
, costing federal agencies $. billion to suppress.
Fire starter
Dry twigs, needles, and moss can combust if they connect with an electrical spark, a discarded cigarette or
an abandoned campfire. High winds can fan flames over larger twigs and brush, followed by branches and
logs—a perfect recipe for a very hot, very intense, multi-day burn.
Living forests are not exempt: they are vulnerable to severe fires during the growing season if two weeks pass
without rain. Mother Nature “sets” fires, too: Lightning strikes are a significant cause of wildfires, particularly
in late summer when the ground is dry.
Large forest fires scorch the soil and send burning embers up to five miles away. Once a forest canopy or
large pile of logs is engulfed, a thick “plume” of pollutant-filled smoke rises into the atmosphere. In the
best case, winds disperse the smoke. In the worst, wind transports the smoke to populated areas, then a
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Page 6
temperature inversion prevents it from vertical
mixing. Wind and weather conditions can be
predicted only up to  hours; after that, it’s
anybody’s guess which way the wind, fire, and
related pollutants will blow.
To better understand fire movement, near-real-time
global fire mapping is helping scientists anticipate
a wildfire event—and prepare for its impacts.
Satellites originally designed to collect weather data
can now observe and monitor dry areas, active
fires, fire hot spots, burned areas, and air emissions
(see the National Oceanic and Atmospheric
Administration Web site for satellite photos at
More than , U.S. weather stations collect and
assess current wildfire conditions, produce fire
danger maps, and make fire weather observations
and next-day forecasts. State and federal agencies
compile data into larger fire-assessment tools and
cooperate with fire watchers worldwide.
Figure 5. Smoke from an Alberta, Canada wildfire
in May  blows southward across the Great
Lakes (seen in the lower right of this satellite
photo), hiding much of Lake Superior from view.
Photo: The Seawifs Project, nasa/Goddard Space
Flight Center and orbimage
Measuring PM in Minnesota
So, as an example, what is being done about it in
the land of , lakes and numerous forests,
located downwind from other particulate sources?
Special pm. monitors are currently measuring
the concentration of fine particles in the ambient
outdoor air. The Minnesota Pollution Control
Agency (mpca) operates pm. monitors in Duluth,
Rochester, St. Cloud, and several Twin Cities
locations. Plans are in the works for monitors in
other regions of Minnesota as well.
“We’ve already learned something interesting from
this monitoring,” says Rick Strassman, supervisor
of the mpca’s air monitoring unit. “Unlike some
other air pollutants, fine particle concentrations rise
and fall rapidly throughout the day and night. This
makes it a challenge to get timely word out to the
public if they need to act.”
In Minnesota, sulfate is an important component
of haze. Nitrate and organic carbon are significant
in winter and summer, respectively. Since some
fine particle pollution blows into Minnesota from
“On a Clear Day You Can See Forever” by Kelley & Helgesen
Figure 6. This composite photo of the St. Paul
skyline provides a visual comparison of two
different levels of fine particles—pm. levels
of µg/m (left) to µg/m (right). Notice the
difficulty in seeing buildings in downtown St. Paul
on the right half of the picture. The daily standard
for pm. is µg/m (micrograms of particles per
cubic meter of air). Photo: Midwest Hazecam
Page 7
other states and some is homegrown, monitors help the mpca learn where particles are coming from, when,
and where they are headed. Imported and homegrown air pollution sometimes combine to create even less
healthy concentrations.
So far, says Strassman, pm. rises to concentrations considered unhealthy for sensitive people (people with
heart or lung disease, older adults and children) no more than a few days a year. “And, knock on wood, we’ve
seen only one day when pm. has risen to the next category, unhealthy for everyone.”
Now that regional pm. monitors are connected to the mpca’s web site (this occurred in summer ),
citizens in each monitored community are able to check local air quality by going to the mpca’s Air Quality
Index (aqi) web page ( The aqi signals if the air quality could adversely
affect you or your family.
The mpca also sends out e-mail Air Pollution Health Alerts when pm. or ozone (at ground level, another
air pollutant) rises to unhealthy levels. Since accumulation of pm. is not dependent upon summer …
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