When we visit a national park or look at the skyline
of a city, often we do not enjoy a clear vista --
a white or brown haze hangs in the air and affects
the view. This haze is not natural. It is caused by
man-made air pollution, often carried by the wind
hundreds of miles from where it originated.
visual range in the eastern U.S. is 15 to 30 miles,
or about one-third of what it would be without manmade
air pollution. In the West, the typical visual range
is 60 to 90 miles, or about one-half of the visual
range under natural conditions. Haze diminishes the
natural visual range.
Haze is caused by fine particles that scatter and
absorb light before it reaches the observer. As the
number of fine particles increases, more light is
absorbed and scattered, resulting in less clarity,
color, and visual range.
types of fine particles contribute to haze: sulfates,
nitrates, organic carbon, elemental carbon, and crustal
material. The importance of each type of particle
varies across the U.S. and from season to season.
The typical importance of each particle type in the
eastern and western U.S. is shown in the figure to
the right. Details on each particle type are provided
below. (Note in the Class I areas in the upper Midwest,
the contributions from nitrates and organics are somewhat
greater and from sulfates somewhat less than indicated
in the figure for the eastern U.S.).
Contribution of Various Particulates to Haze
in the air from sulfur dioxide gas. Most of this gas is
released from coal-burning power plants and other industrial
sources, such as smelters, industrial boilers, and oil
refineries. Sulfates are the largest contributor to haze
in the eastern U.S., due to the region's large number
of coal-fired power plants. In humid environments, sulfate
particles grow rapidly to a size that are very efficient
at scattering light, thereby exacerbating the problem
in the East.
carbon particles are
emitted directly into the air and also form there as a
reaction of various gaseous hydrocarbons. Sources of direct
and indirect organic carbon particles include vehicle
exhaust, vehicle refueling, solvent evaporation (e.g.,
paints), food cooking, and various commercial and industrial
sources. Gaseous hydrocarbons are also emitted naturally
from trees and from fires.
form in the air from nitrogen oxide gas. This gas is released
from virtually all combustion activities, especially those
involving cars, trucks, off-road engines (e.g., construction
equipment, lawn mowers, and boats), power plants, and
other industrial sources. Like sulfates, nitrates scatter
more light in humid environments. Nitrate contributes
relatively more to particle light extinction in winter
than in summer because of its chemical properties (i.e.,
ammonium nitrate is more stable and less likely to dissociate
at lower temperatures than at higher temperatures).
are very similar to soot. They are smaller than most other
particles and tend to absorb rather than scatter light.
The "brown clouds" often seen in winter over urban areas
and in mountain valleys can be largely attributed to elemental
carbon. These particles are emitted directly into the
air from virtually all combustion activities, but are
especially prevalent in diesel exhaust and smoke from
the burning of wood and wastes.
is very similar to dust. It enters the air from dirt roads,
fields, and other open spaces as a result of wind, traffic,
and other surface activities. Whereas other types of particles
form from the condensation and growth of microscopic particles
and gasses, crustal material results from the crushing
and grinding of larger, earth-born material. Because it
is difficult to reduce this material to microscopic sizes,
crustal material tends to be larger than other particles
and tends to fall from the air sooner, contributing less
to the overall effect of haze.
generally appears either as uniform haze, layered haze,
uniform haze degrades visibility evenly across
the horizon and from the ground to a height
well above the highest features of the landscape.
Uniform haze often travels long distances
and covers large geographic areas, in which
case it is called a regional haze.
a layered haze, you can see the top edge of
the pollution layer. This is often the case
when pollution is trapped near the ground
beneath a temperature inversion.
result from local sources. Plumes and plume-like
layers of elevated pollution take their shape
under certain meteorological condition where
the air is stable or constrained.
of the pollutants that form haze have been linked to serious
health effects and environmental damage. Exposure to fine
particles in the air have been linked with increased respiratory
illness, decreased lung function, and premature death.
In addition, sulfate and nitrate particles contribute
to acid rain, which can damage forests, reduce fish populations,
and erode buildings, historical monuments, and even car
reduce haze we must reduce emissions of haze-forming pollutants
across broad areas of the country. Cars, trucks, and industries
are much cleaner than they were in the past, and several
programs are in place to maintain this progress over the
next several years. Nonetheless, these programs by themselves
are unlikely to restore visibility to its natural conditions
in may protected areas.
April 1999 the U.S. Environmental Protection Agency (EPA)
issued regulations to further reduce haze and protect
visibility across the country. Given the effect of regional
pollutant transport in contributing to haze in Class I
areas, USEPA encourages states to work together in regional
partnerships to develop and implement multi-state strategies
to reduce emissions of visibility-impairing fine particle
pollution. Five Regional Planning Organizations (RPOs)
were formed to implement the regional haze regulations.
The Midwest RPO is led by the States of Illinois, Indiana,
Michigan, Ohio, and Wisconsin, and the tribes located
in these states. Federal Land Managers, USEPA, and stakeholders
also participate in the regional planning process.
regional planning process will consist of three phases:
During the first year or so of regional planning, the
Midwest RPO has worked to "get organized"
and "get smart". This initial phase included
some preliminary work to build the technical foundation
for regional planning.
This phase, which is expected to take place over
the first five years or so, will involve collecting
and reviewing monitoring data, developing an emissions
inventory, and analyzing future year emissions reductions
scenarios using models or other appropriate methods.
These activities are designed to meet several objectives:
(a) develop an understanding of current pollution
levels, (b) identify the principal contributing
sources, (c) determine which states or areas contribute
to another states visibility problem, and
(d) estimate the impact of future strategies on
air quality, costs, and other factors.
This phase, which will take place after the technical
assessment phase is completed, will include the
development and submittal of the following SIP documents:
SIP (due 1 year after PM2.5 designations)
that emissions from your state contribute
to visibility impairment in Class I area in
another state (or emissions from another state
contribute to visibility impairment in Class
I area in your state)
regional planning process
of BART-eligible sources
to submit control strategy SIP by appropriate
Strategy SIP (due 3 years after PM2.5 designations)
reasonable progress goals to ensure improvement
for most impaired days and no degradation
for least impaired days
baseline and natural visibility conditions
for most and least impaired days
Reports (every 5 years)
progress toward reasonable progress goal;
reinitiate regional planning, if not "on
SIP Revision (every 10 years)
and reassess control strategy SIP
are challenged to do our part to help reduce air pollution.
To learn more about what you can do to reduce air pollution,
click on http://www.epa.gov/air/actions.