Visual Air Quality
Big Bend National Park
Big Bend – A Land of Borders
Big Bend
Natl. Park
One of the largest and least-visited national parks, Big Bend encompasses over 800,000 acres
in southwest Texas. Situated on the northern banks of the Rio Grande it is the meeting place
of nations and cultures. Three states come together at Big Bend: Texas in the United States,
and Coahuila and Chihuahua in Mexico. Because of it’s unique character, Big Bend was
designated a Desert Biosphere Reserve in 1976.
Big Bend – A Land of Panoramic Views
South Rim View
Big Bend – A Land of Panoramic Views
Casa Grande
Big Bend – A Land of Panoramic Views
Juniper Canyon – The Boot
Big Bend – A Land of Panoramic Views
Sierra Del Carmen Mountains - Mexico
Big Bend – A Land of Panoramic Views
Chisos Basin
Visibility:
Defining the Problem
Big Bend – Air Pollution
Although remote, Big Bend is not immune to urban problems like air pollution.
Big Bend – Air Pollution
On many days, haze hangs over much of Big Bend’s landscape,
obscuring the panoramic views many visitors seek.
Big Bend – Air Pollution
On some days during the summer the park experiences
the worst visibility of any western national park.
It’s Hazy and Getting Hazier
Clear day
Views
throughout
the park are
impacted to
some degree
most of the
time.
Hazy day
It’s Hazy and Getting Hazier
Clear day
Most visitors
believe the
haze is
natural.
It’s not.
The primary
cause is
human
activity.
Hazy day
It’s Hazy and Getting Hazier
Clear day
Noticeable
changes in
air quality
appeared
around the
turn of the
century in
many areas
of the U.S.
Hazy day
It’s Hazy and Getting Hazier
Clear day
Park
managers
began
monitoring
the air at
Big Bend
in 1978.
Hazy day
It’s Hazy and Getting Hazier
After years of
data
collection
and analysis,
researchers
are beginning to
understand
what causes
the pollution
contributing
to the park’s
Clear day
visibility
problem and
consider the
sources both
near and
distant.
Hazy day
How Far Can You See?
Dagger Mountain
17 Miles
Good Day – over 100 miles
It’s this good or better 10% of the time.
Average Day – (65 –75) miles
Most visitors will see this.
Worst Days – 35 miles
It’s this bad or worse 10% of the time.
Visibility
Concepts
What is Visibility?
Visibility is
historically defined
as:
“the farthest
distance one can
see a large black
object against the
background sky.”
What is Visibility?
Molecules in the
earth’s
atmosphere scatter
light, limiting the
maximum distance
you can see even
under under
natural conditions.
The theoretical limit of visual range is 243 miles.
The scattering of
light by air
molecules is called
“blue sky” or
“Rayleigh”
scattering.
Visual Range
What is Visibility?
Visibility is more
than just how far
we can see. It is
better described as
how “well” we can
see and appreciate
the colors,
textures, forms,
and detail in
distant landscape
features.
Visual Range
Three Types of Haze
Visibility Impairment: generally associated with
Plume: Pollutants are constrained in a tight
discoloration, haziness, and loss of color and detail.
elevated layer that can often be traced to a nearby
source.
Uniform Haze: Pollutants are uniformly
Layered Haze: Pollutants are often trapped
distributed from the ground to a height well above
the highest terrain feature.
near the ground beneath a temperature inversion.
The top edge of the pollutant layer is visible.
How impairment manifests itself depends upon the extent
and distribution of particles and gases in the atmosphere.
How Pollutants Cause Haze
Particles and gases in
the atmosphere can
scatter or redirect
image-forming light as
it travels to the eye.
Through scattering,
some image-forming
light is removed from
the view path.
Scattering
In addition, extra light,
sunlight, and light
reflected from the
clouds and ground are
added to the sight path,
which interferes with
the ability to view the
scene.
Scattering in the Atmosphere
How Pollutants Cause Haze
Another cause of
visibility impairment is
absorption.
Particles and gases in
the atmosphere absorb
or remove imageforming light before it
ever reaches the
viewer’s eye.
Absorption
Although significant,
absorption usually is
less important than
scattering processes
when we talk about
visibility impairment.
Absorption in the Atmosphere
How Pollutants Cause Haze
Extinction is a visibility
metric used to describe
the combined effect of
scattering and
absorption. It is
proportional to the
total amount of light
removed as light passes
through the
atmosphere and is
related to the
concentration of
pollutants.
Extinction
Parameters Describing Visual Air Quality
Deciview is an index
of haziness that
expresses changes in
scene quality. It is
directly related to
perceived changes in
visibility. As haziness
increases, so does the
deciview value.
A one deciview
change represents a
10 percent change in
extinction. Most
people can perceive a
one deciview change.
1. Visual Range
2. Extinction
3. Deciview
Microscopic Airborne Particles
Particles fall into two size
categories:
1. Coarse Particles
greater than 2
micrometers and less than
10 micrometers
(These particles usually
deposit out of the air close
to their source.)
2. Fine Particles
2.5 micrometers and
smaller
(These particles can stay
suspended for weeks and are
transported far from
their source.)
Examples of particles that affect visibility
Particle Size Matters
Fine
particles
scatter light
more
efficiently,
and there
are a lot
more of
them. They
are most
important
when
assessing
visibility
impacts.
Base Case –
Clear atmosphere
Increasing the mass
of coarse particles
(dust) by a certain
amount has little
effect on visibility in
this scene.
Increasing the mass
of fine particles
(sulfur) by the same
amount has a much
bigger effect on
visibility in the
same scene.
Five Particle Types that Reduce Visibility
Although particulate matter is made up of
many chemical species, there are five key
contributors to visibility impairment.
Primary Pollutants are emitted directly
into the atmosphere, and include:
1.
2.
3.
4.
5.
Sulfur Dioxide
Nitrogen Oxides
Elemental Carbon
Organic Compounds
Soil or Dust
Secondary Pollutants form from
chemical reactions involving primary
gas emissions (precursors), and include:
1. Ammonium Sulfate
2. Ammonium Nitrate
3. Organic compounds
Secondary Particle Formation
Precursor emissions disperse in the atmosphere, convert into secondary
particles through complex atmospheric chemical reactions, then travel
long distances to deposit in remote areas far from their source.
Sulfate Formation and Growth
Ammonium Sulfate
forms from sulfur
dioxide gas emissions.
Oxidation of SO2 to
sulfate can be slow,
requiring 1 to 2 days
to convert about half
of the SO2. In the
presence of mist, fog,
or clouds,
transformation can
occur in a few hours
or in several minutes.
Nitrate particles are created in much the same way from nitrogen oxide gases.
Organic particles similarly evolve from gaseous emissions of hydrocarbon gases.
Relative Humidity Affects Visibility
Dagger Mtn.
10% RH
visual range = 35 mi.
Fine sulfate and nitrate particles
are hygroscopic. They readily
attract and absorb water
molecules. Under high relative
humidity conditions, they
quickly grow to a size that is
very efficient at scattering light.
The fine sulfur levels in all views
is the same (20 g/m3). The
relative humidity changes from
10% to 50% to 90%.
Dagger Mtn.
50% RH
visual range = 27 mi.
Dagger Mtn.
90% RH
visual range = 10 mi.
Sources of Visibility-Reducing Pollutants
Policies Aimed at
Improving Visibility
National Park Service Organic Act
August 26, 1916
“… to conserve the scenery and the
natural and historic objects and
the wildlife therein and to provide
for the enjoyment of the same in
such manner and by such means
as will leave them unimpaired for
the enjoyment of future
generations.”
Big Bend National Park
Authorized by Congressional Act
June 20, 1935
“…lands…as necessary for
recreational park
purposes...are hereby
established, dedicated, and set
apart as a public park for the
benefit and enjoyment of the
people.”
Clean Air Act
1970 Act
Established special goals for visibility in national parks,
wilderness areas, and international parks.
1977 Amendments
Set a goal to achieve natural visibility conditions: the prevention of
any future, and the remedying of any existing, visibility impairment
in mandatory Class I federal areas in which impairment results
from man-made air pollution.
The Amendments required the EPA to issue regulations to assure
“reasonable progress” toward meeting the national goal of no
human-caused emissions.
1990 Amendments
Expanded the focus to include mitigating regional haze, an issue
encompassing multiple sources located within multiple jurisdictions
and under the purview of multiple institutions.
Regional Haze Rule
April 1999
Addresses visibility impairment
in the form of “regional haze”
The rule calls for states to work together to improve
visibility in all mandatory Class I national parks and
wilderness areas. States are encouraged to work
together in regional partnerships to develop and
implement multi-state strategies to reduce emissions of
visibility-impairing fine particle pollution.
Additionally, states must determine whether or how
much emissions from sources in a given area affect
visibility in a downwind Class I area.
What is the
Park Doing?
IMPROVE
Interagency Monitoring of Protected Visual
Environments
The park’s goal is
to develop a
sound visibility
database in order
to establish
current visibility
levels, examine
trends, and
compare
visibility at Big
Bend to other
remote areas of
the United States.
Big Bend has been part of the IMPROVE national monitoring program since 1981.
Visibility Monitoring - Optical
Transmissometers
and nephelometers
are used to record
the optical
characteristics of the
atmosphere –
measuring the
amount of light
transmitted over a
specific viewing
path.
Transmissometers measure extinction.
Nephelometers measure
scattering.
Visibility Monitoring - Aerosol
Aerosols are microscopic solid and liquid
particles suspended in the air. Measurements of
these particles help to identify which particles
are reducing visibility.
Particles are collected on filters in various size
ranges. A profile of particle types, sizes, and
concentrations can be obtained.
IMPROVE fine particle monitor
Visibility Monitoring - View
Big Bend operated a 35 mm
camera from 1981–1985.
Photographs were taken 3
times a day. 8 mm time-lapse
movies recorded dynamic
scene changes for several
years.
Big Bend now operates two web
cameras that transmit data and
live pictures of current visibility
conditions to the web. The view
of the Sierra Del Carmens
updates every 15 minutes, while
the view from the Chisos Basin
updates every 30 minutes. View
the website at:
www2.nature.nps.gov/air/webcams/parks/bibecam/bibecam.htm
Photography documents the changing appearance of a scene as visibility levels vary,
documenting changes in haze levels, lighting conditions, vegetative cover, & cloud effects.
Other Air Quality Monitoring
Ozone is measured in
the atmosphere on a
continuous basis.
A dry
deposition
monitor
measures
nitrates,
sulfates,
ammonium,
sulfur
dioxide,
and nitric
acid in the
atmosphere.
Rainfall chemistry analysis
began in 1980 and is part of
a nationwide system that
monitors changes in
chemistry and acid content
of precipitation.
A UV spectrophotometer
measures UVB radiation to
assess the effects of
environmental stressors on
ecological systems.
Monitoring
Results
National Visibility Trends, 1990–1999
20% Clearest Days -- Best Visibility Conditions
Over a 10-year period most parks show
some improvement in average haze levels
on the clearest days. Big Bend is one of
three parks that shows continued
degradation on these days.
20% Haziest Days -- Worst Visibility Conditions
Most parks show some degradation (or
worsening) of visual conditions on hazy
days over the same period. Note that
visibility degradation in the southwest is
particularly significant and that Big Bend
is one of three parks where haze is getting
worse.
Annual Aerosol Extinction, 1996–1998
Inner Mountain
West
Big Bend has some
of the worst haze in
the western United
States.
Compare:
Big Bend
(28 Mm-1)
Big Bend
To:
Inner Mountain
West (15 Mm-1)
Extinction is proportional to image-forming light lost over a unit of distance.
Higher light extinction levels correspond to hazier conditions.
Fine Mass
Big
Bend
Particulate
matter
observed
during BRAVO
and supported
by long-term
IMPROVE
monitoring
indicates that
visibility is
dominated by
fine particles,
but at times
there are
significant
contributions
from coarse
dust particles.
Fine particles sampled at Big Bend consist mainly of ammoniated sulfate and organic
carbon with black carbon, soil dust, and nitrate particles as minor factors.
Sulfate Mass
Sulfate Fraction of Fine Mass
On an annual average, sulfates
account for between 40 and 50%
of the fine mass at Big Bend.
Sulfate compounds result from direct
emissions of sulfur dioxide and generally
contribute more to haze than any other
individual pollutant. The oxidation of
SO2 to sulfate depends on the oxidative
capacity of the atmosphere which is
influenced by NOx and volatile organic
carbon emissions.
Organic Mass
Organic Fraction of Fine Mass
On an annual average
organics constitute 20–30% of
the fine particles creating Big
Bend haze.
Carbonaceous particles, organic
compounds, and light-absorbing carbon
(LAC) generally constitute the second
largest individual component
contributing to haze at Big Bend.
Soil Mass
Soil Fraction of Fine Mass
On an annual average dust
contributes about 20–30% to
haze-causing particles at Big
Bend.
Dust – a combination of fine soil and
coarse mass – contributes significantly
to haze during the springtime months
of March and April. Dust is
transported from both local and
international sources.
Monitoring Trends
at Big Bend
National Park
Trends in Extinction
at Big Bend from 1990–2002
Trends in Sulfur Dioxide Emissions
and Measured Sulfate
70
Particulate Bext (1/Mm)
60
Worst haze days
visibility 37–47 mi.
16 1/Mm / 10 yr
50
40
Average haze days
visibility 65–69 mi.
4.3 1/Mm /10 yr
30
20
10
Insignificant
0
90
92
94
Clearest days
visibility 91–118 mi.
96
98
00
02
Year
The open symbols are annual values and
the closed symbols are a 5-year moving
average. The number of very hazy days
has steadily increased over the last decade
and the bad days are getting worse.
Sulfate concentrations and sulfur dioxide
emission trends closely track each other.
Emission rates in Texas and bordering states
show significantly increasing trends. Between
1991 and 1999 there was a steady increase in
sulfate of about 15% and a corresponding 15%
increase in sulfur dioxide emissions over the
region. Big Bend data shows a 37% increasing
trend in measured sulfates. It is one of the few
parks where both sulfates and haze are
increasing.
Big Bend Extinction Budget, 1998–2002
Particle Extinction Mm-1
Par
tic
ula
te
Ext
inc
tio
n
(M
m1)
50
Spring Peak (April-June)
45
Fall Peak (August-October)
40
35
30
25
20
15
10
5
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Big Bend sulfate compounds
contribute more to haze
than any other component.
Carbonaceous matter
(organic compounds and
light-absorbing carbon
(LAC)) constitute the
second largest component of
haze.
Information from other
studies shows that biomass
burning in Mexico and
Central America
(Mm-1)
contributes to carbonaceous
Soil
Coarse
Amm. Nitrate
Organics
Amm. Sulfate
LAC
Amm.
Amm.
Organics
LAC
Soil Coarse matter in late spring. Dust
Sulfate
Nitrate
(a combination of fine soil
and coarse mass)
There are two periods of high haze at Big Bend National Park:
contributes significantly to
spring (when sulfate and carbonaceous compounds contribute
haze during March and
similar amounts to haze), and late summer/fall (when particulate
sulfate compounds are the largest contributors to haze). 63% of the April.
haziest days occur in the 2nd and 3rd quarters.
Big Bend Extinction Budget, 1998–2002
All Days
1/5 haziest Days
15%
17%
5%
Coarse
6%
Sulfate
6%
48%
Organics
Coarse
5%
Organics
4%
5%
Ext = 28.8 Mm-1
Nitrate
53%
18%
18%
Sulfate
Sulfate
Organics
LAC
Soil
Sulfate
LAC Soil
Ext =Organics
54.4 Mm-1
Nitrate
Coarse Mass
Coarse Mass
Fine particles sampled in the Big Bend NP region are mainly ammoniated sulfate
and organic carbon with black carbon, soil dust, and nitrates forming minor
contributions. Coarse particles appear to be mainly soil dust.
Sulfate is the single largest contributor to haze at Big Bend. Particulate sulfate contributes
more to extinction on the haziest days than on average days.
Special
Study
BRAVO Study, July–October, 1999
Big Bend
Regional
Aerosol &
Visibility
Observational Study
Because sulfates are the major
chemical component of visibility
reducing particles, the study focused
on sulfate production mechanisms
and the relative contribution SO2
sources to visibility impairment in
Big Bend National Park. It should be
acknowledged that organic carbon
and coarse particles also play a role
in visibility reduction.
BRAVO Study Objectives
• Understand the long-range trans-boundary transport of
haze from regional sources in the U.S. and Mexico
– Determine the role of meteorology on Big Bend haze
– Identify the most likely pollutant transport corridors associated
with Big Bend haze
• Quantify (model) the contribution of specific U.S. and
Mexican source regions and source types responsible for
Big Bend’s haze
– Mexican Carbón I/II power plants
– Industrial source areas on the Texas gulf coast and in Monterrey
and Tula, Mexico
– Coal-fired power plants and refineries in Texas (Lignite Belt)
– Large SO2 source regions in the southeastern and midwestern U.S.
Potential Source Areas of Haze at Big Bend
Carbón I - Mexico
Carbón II - Mexico
A terrain map of Texas and Mexico showing some major cites and potential source areas of
haze that could be contributing to haze at Big Bend National Park
BRAVO Network Configuration
Tracer Release and Monitoring Sites
To track pollutants, tracers were released from
specific source regions in Texas and Mexico.
BRAVO Network Configuration
Gas and Aerosol Sampling Locations
Measurements were made at 37 sites over a 4-month
period followed by 4 years of data analysis.
BRAVO Study Site at KBar
Measurements were made of speciated fine particles, gases,
light scattering and absorption, particle size distributions,
meteorological parameters, and tracer concentrations.
BRAVO Emissions Inventory, U.S. / Mexico
SO2 sources include power plants
along the Ohio River Valley in the
eastern U.S. and eastern Texas.
Sources in Texas include coalfired power plants, oil refineries,
and carbon black producers.
More power plants are located
near a lignite belt running from
northeast Texas towards the
Mexican state of Coahuila. There
are also several large point
sources in northern Mexico (250
km from the park), including
coal-fired power plants, fuel oil
refining and combustion
operations. The Carbón I &II
power plants, near the U.S.Mexico border, are the largest
coal combustion facilities in
Mexico.
BRAVO Emissions By Source Region
SO2 Emissions by Source Region
1.9E+07
2.0E+07
area
point
total
1.8E+07
1.5E+07
1.4E+07
SO2 Emissions [Mg/yr]
1.6E+07
1.4E+07
1.2E+07
1.2E+07
1.0E+07
8.0E+06
6.0E+06
4.0E+06
2.5E+06
4.0E+06
1.0E+06
1.7E+06
2.5E+06
2.0E+06
9.2E+05
0.0E+00
1.8E+06
total
1.2E+06
8.5E+05
ALL
EMISSIONS
1.3E+05
EASTERN
US
point
5.1E+05
area
MEXICO
TEXAS
Region
WESTERN
US
Numerous methods were used to identify source types and source regions
that contribute to sulfate haze at Big Bend. SO2 sources are defined as either
elevated point sources (coal-fired power generation) or area sources (diesel
combustion from mobile sources).
Newly Built and Proposed
New Power Plants in Texas
Local, Regional, & International Transport
Transport of Los
Alamos smoke in
elevated dry layer
NAAPS Simulation of
Los Alamos Smoke Plume,
May 12, 2001
Transport of
Central American
smoke in low-level
moist layer
Asian Dust Plume
Central
Texas
Smoke
Impact
A large dust
storm on
Coarse
April 6–7,
Sulfate
2001, then
Organics
swept across
East Asia, the
Pacific, and
North
America
Smoke and dust is a regional issue with distant sources contributing
to the haze in Big Bend. Pollutants generally remain in the air for
3 to 7 days and can be carried thousands of kilometers by the winds.
Models: Linking Emissions to Measured Pollutants
Source models start with known emissions and try to predict where pollutants will go
and how they will change during the journey to a park (or receptor). Receptor models
venture backward in time by measuring pollutants at the receptor and simulating the
path the air mass took to get there.
Receptor
Concentration
=
Dilution
*
Chemistry/
Removal
*
Emissions
Source contribution to
receptor concentration
Pollutants are emitted from a source, transformed in the atmosphere, and transported
with the winds. Along the way they become diluted
or may deposit out as dry particles, or in rain, fog, or snow.
Models: Transport Pathways
(Mm-1)
Click on map to play/stop movie
Computer models used National Weather Service wind data to look at airflows over North
America on days preceding high sulfur episodes at Big Bend National Park.
Simulated Tracer Release
Regional transport results in the mixing
of emissions from distant sources which
can be more than 1000 km apart. The
highest concentrations from a single
source region often occur under
stagnant winds which allow the
emissions to accumulate near the
sources. Re-circulating transport
patterns and flow reversals also allow
for the accumulation and mixing of
emissions from multiple source regions.
Pollutants can then be transported to
downwind receptor sites, resulting in
elevated pollutant concentrations.
Big Bend NP
Click on map to
play/stop movie
This animation illustrates the transport
and diffusion of plumes from four Texas
source regions. This event
demonstrates how southerly flow
transports the plumes north, mixing
them together. The flow reverses,
passing over the sources again and
allowing the pollutants to
accumulate. The pollutants are then
transported to Big Bend National Park.
Modeled Big Bend Source Attribution
The sulfur oxide sources of influence on visibility at Big Bend NP are highly variable during
the year. The BRAVO study found that under easterly wind conditions the eastern U.S. and
sources along the northeastern border of Mexico often contribute to haze. Texas also
contributes part of the time, and the Carbons’ contributions were larger than any other
single SO2 emissions facility.
Total Haze Attribution (1/Mm)
Big Bend’s Sulfate Haze Source Attribution
100
80
Organics + LAC + Nitrates +
Fine Soil + Coarse
Sulfate Haze Source Attribution
Carbón
Other Mexico
Texas
Eastern US
Western US
Other
Rayleigh
60
40
20
0
July 9
August 9
September 9
October 9
Eastern US
Mexico
Total Haze Attribution
Texas
100%
90% Rayleigh
80%
70%
60%
50%
40%
30%
20%
10%
0%
July 9
Scatter: Haze due to scattering by pollutant-free air
August 9
Mexico
September 9
October 9
Western US
Mexico’s contribution
to Big Bend sulfate was
relatively high during
times when average
sulfate concentrations
were lower than
average.
The Texas and eastern
U.S. sources tended to
contribute to Big Bend
during the highest
sulfate concentrations.
Low sulfate days were
dominated by
contributions from
Mexico in July-Sept.
At the end of Sept. and
Oct., the western U.S.
was also a major
contributor on low
sulfate days.
Contribution to Big Bend’s Haze - BRAVO
Western
US 2 %
Percent contributions to particulate haze are in parentheses
• Sulfate contributes 21% of the haze on clear days (Mexico: 10%, U.S.: 8%).
• Sulfate contributes 47% of the haze on hazy days (Mexico: 14%, U.S.: 31%).
The relative contributions to light extinction by eastern U.S. and Texas sources of
particulate sulfate at Big Bend increase by factors of about 4 and 5, respectively, on the
haziest days compared to the least hazy days of the study period.
Clear Day – Pollution Free
Average Low Haze Day - BRAVO
On average low haze days, sulfates contribute 22% of the haze.
Mexican sources contribute about half the measured sulfates.
Average High Haze Day - BRAVO
On average high haze days, sulfates again contribute 44% of the haze. Sources in Mexico
and the eastern U.S. are the largest contributors to sulfates at Big Bend NP.
What is Causing Big Bend’s Haze?
Shipping –
Harbor
Activity
Railroads – Diesel Emissions
Urban Activity
Power Plants –
Especially Coal-Fired
Plants
Refining and
Industrial Manufacturing
Power Plant Emissions –
Transport from Mexico
What is Causing Big Bend’s Haze?
• Sulfate is the single largest contributor to haze at Big Bend NP.
• Big Bend is one of the only national parks where sulfates are increasing.
• Some of the highest haze episodes during the spring season are caused by
international transport of dust and smoke.
Common Transport Pathways...
• Throughout the year air masses en route to Big Bend frequently reside
over Mexico, particularly northern Mexico.
• Airflow from eastern Texas and the eastern U.S. is most frequent during
late summer and fall months, during the period with the greatest
contribution to haze by sulfate particles.
• Airflow from the western U.S. to Big Bend is greatest in the winter
months when haze levels at the park are lowest.
• The highest sulfate haze periods during BRAVO were associated with
low speed and low level transport from the the eastern U.S., eastern
Texas, and northeastern Mexico.
• The lowest sulfate haze periods during BRAVO were associated with
higher speed transport from the Gulf of Mexico up along the
Mexican/Texas border to Big Bend and from the western U.S.
that Bring Pollutants to Big Bend Natl. Park
Where Does the Sulfate Haze Come From…
• At any given time, over half of the sulfate haze can come from either
the eastern U.S., eastern Texas, or Mexico.
• During the BRAVO study period, the eastern U.S. and eastern Texas
are responsible for ~50% on average and more on the high sulfate days
of Big Bend’s sulfate haze during the BRAVO study period.
• At 20%, the Carbón power plant is the single largest contributor to Big
Bend’s sulfate haze, during the BRAVO study period.
• On the clear days, Mexico and the western U.S. are the largest
contributors.
at Big Bend National Park?
How Can Visibility be Improved…
• Control SO2 emissions from the Carbón power plants.
• Significantly reduce SO2 emissions in both east Texas and the eastern
U.S.
• Reductions in SO2 emissions in northern Mexico and the western U.S.
can significantly improve Big Bend’s clear days.
• To address the U.S. regional haze rule, Texas will need to seek
agreements for sulfur oxide reductions regionally within the U.S. and
with Mexico in addition to achieving SO2 reductions within the state.
As SO2 emissions are reduced, the role of organic carbon and coarse
soil in reducing visibility will become increasingly important.
at Big Bend National Park?
What Can You Do?
• Stay informed about air quality issues that may affect the park.
• Let federal, state, and local government officials know that air quality
is important to you. Support ballot measures and candidates sensitive
to air quality issues.
• Learn about local efforts to see what is being done in your area.
• During your visit to Big Bend, join a ranger for a guided walk or
evening presentation to learn more about other issues affecting park
resources.
• Conserve energy at home and at work. Use energy efficient appliances
and lighting when possible. Ask your utility company about its
customer energy conservation program
• Keep your car engine tuned and maintain the correct tire pressure.
Use an energy-conserving grade motor oil and “clean” fuels. Drive at a
medium speed; most cars operate most efficiently between 35–55 miles
per hour.
Be Involved!
What Can You Do?
Concerned Citizens Against Pollution at Texas State Capitol,
Austin, TX.
Be Involved!