Airports are known to be major
sources of noise, water, and air pollution. They pump carbon dioxide (CO2),
volatile organic compounds (VOCs), and nitrogen oxides (NOx) into
the atmosphere, as well as dump toxic chemicals—used to de-ice airplanes during
winter storms—into waterways. But determining the extent of airplanes'
contribution to local, national, and international levels of pollution is
difficult—cars and airplanes entering and leaving airports produce roughly
equivalent quantities of ozone precursors. Auxiliary power units (APUs), little
jet engines in the planes' tails that power appliances while the planes are at
the gate, and ground support vehicles also produce quantities of pollutants.
And competing local and national political forces make airport pollution hard
to regulate; much of the air pollution is local, but automobile and airplane
emissions are regulated both nationally and internationally.
The growth of air traffic further
frustrates mitigation of environmental problems. Air traffic is expected to
double nationally by the year 2017 and internationally by 2010, according to
the Federal Aviation Administration (FAA). At least 32 of the 50 busiest U.S.
airports have plans to expand operations, according to a survey conducted by
the Natural Resources Defense Council (NRDC), published in the environmental
group's October 1996 report Flying Off Course: Environmental Impacts of
America's Airports. According to the FAA, 60 of the 100 biggest airports want
to at least build or extend runways.
In 1993, aircraft emitted 350 million
pounds of VOCs and NOx during landing and takeoff cycles, more
than double 1970 levels, according to the NRDC report. These two classes of
compounds are precursors of ground-level ozone, which can interfere with lung
function. "During the summer . . . between 10% and 20% of all East Coast
hospital admissions for respiratory problems may be ozone-related," says
the NRDC report.
Airports are among the greatest sources of
local air pollution. A major airport's idling and taxiing planes can emit
hundreds of tons of VOCs and NOx annually. John F. Kennedy
International Airport is the second largest source of VOCs in New York City.
LaGuardia is among the major sources of NOx.
The VOCs emitted by airports may comprise a
variety of toxic chemicals, according to a 1993 study by the EPA. Chicago's
Midway Airport released more benzene
and formaldehyde than most Chicago
factories. But Jacob Snow, assistant director of aviation for planning and
environment at McCarran International Airport in Las Vegas, Nevada, asserts
that in the world of ozone precursor emissions, those from airports are of
little consequence. "McCarran's VOC emissions [for 1993] were equivalent
to those [produced by] the motor vehicles used by less than 9% of the
nonattainment basin's households," he says. Similarly, a 1991 study by
Argonne National Laboratory, funded by the FAA, concluded that "the impact
of airport emissions on the surrounding air quality was not significantly
larger than that of the background emissions. This implies that on a per-unit
area of ground surface basis, the airport emissions are roughly comparable to
those of the surrounding urban/suburban areas and roadways."
And, in fact, ground access vehicles such
as passenger cars and buses just entering and leaving airports often exceed
airplanes as the dominant sources of air pollution at airports. Nationally,
ground access vehicles emit 56% of VOCs, while aircraft taking off and landing
give off only 32.6% (including
emissions from APUs), according to the EPA. Ground access vehicles emit 39.3% of NOx, trailing
closely behind emissions by aircraft and APUs of 46.3%.
Ground service equipment is responsible for
10.9% of airport-generated VOCs and 14.3% of NOxnationally,
according to the EPA. National figures for APUs were not available, but in
southern California in 1990, APUs gave off less than 1% of hydrocarbons and
about 6% of NOx, according to the California Air Resources Board
(CARB).
In 1993, one out of five U.S. citizens
lived in a locale where air failed to meet national standards for ozone. Thirty
of the nation's 50 busiest airports are located in ozone nonattainment areas,
and three of these are located in the dirtiest nonattainment area, the Los
Angeles-South Coast basin.
States that include nonattainment
areas must develop state implementation plans (SIPs) for cleaning their air.
But states have scant leverage to deal directly with airport pollution. States
cannot regulate aircraft emissions for the same reason they cannot regulate
automobile emissions. "Can you imagine every airport imposing different
standards on 737s?" asks Ken Feith, senior scientific advisor in the EPA's
office of air and radiation. So what can a SIP do? "If an airport is owned
and operated by a state or local political jurisdiction, that jurisdiction has
total control over ground equipment," says Feith. "They can impose
restrictions as long as they don't interfere with flight operations." For
example, that jurisdiction can limit a terminal's number of gates.
One measure that could reduce
emissions is single-engine taxiing. Single-engine taxiing saves fuel and
reduces emissions substantially. Delta Airlines pilots generally use one engine
to taxi, and at the airline's hub in Atlanta, this strategy saved $5.9 million
in fuel costs in 1995 alone, according to the NRDC. But other airlines eschew
or minimize the practice. Some airplanes lack the ability to taxi on one
engine, says James Ericson, director of the office of environment and energy at
the FAA. Furthermore, crews must be properly trained in the technique. Albert
Prest, vice president of operations for the Air Transport Association, a trade
group, says that the practice can be dangerous in certain circumstances, such
as wet weather, because it may encourage the plane to slide or veer to one
side.
The Case in California Top
But with 25-30 year lifetimes for
jets, emissions from airplane engines will remain a problem long after the 2010
deadline for SIPs for extremely polluted areas such as Los Angeles to achieve
air quality standards. According to projections by the CARB, aircraft NOx emissions at so-called South Coast
(the southern coast of California) airports will have doubled in 2010 over 1990
levels, to 24.8 tons per day or about 13% of 1990 levels. The board expects
hydrocarbon emissions to drop somewhat, from 7.0 to 5.4 tons per day.
In contrast, the board expects
ground access vehicle NOx emissions,
mostly from automobiles, to drop to 2.4 tons per day, or about one-quarter of
1990 levels. The projected reductions are due to California's stringent
automobile air quality standards. But critics say the figures are optimistic
because they assume a slower rate of growth than is actually occurring.
California's efforts illustrate the
difficulties of cleaning air as population and travel explode. The California
SIP incorporates a 50% increase in air traffic in the South Coast region, says
Henry Hogo, planning manager for the South Coast air quality management district.
"We try to balance economic needs with health," he says. "We
want to allow growth and see if we can come up with ways of reducing
emissions."
Nonetheless, in 1994 the state asked
for the federal government's help to curtail reductions in federally regulated
interstate transportation sources such as trucks and airplanes, says Hogo. A
consultative process was set up between the South Coast district, the CARB, and
the EPA to figure out how to achieve the necessary reductions. "The state
assigned to the EPA the responsibility to reduce emissions from aircraft
engines by a total of 8 tons per day through new standards," says Doris
Lo, an environmental engineer in the EPA's Region IX. But a 16% reduction in
emissions, recently proposed by the International Civil Aviation Organization,
would not come close to delivering the required reduction. The proposed
reduction is being opposed by two U.S. engine manufacturers—Pratt & Whitney
and General Electric—as well as by the FAA, and is unlikely to be implemented.
The EPA is looking elsewhere for the
8 tons. The easiest emissions reductions could be had by powering ground
service equipment with electricity and alternative fuels, and having aircraft
at the gate plug into the terminal "instead of running those dirty [auxiliary]
engines," says Lo. Nonetheless, these two sources represent a small
percentage of VOCs and NOx, and, so far, less than a ton per day of
possible reductions has been identified.
Politics have stifled the South
Coast district's own efforts to manage local air quality planning, critics
charge. "The state legislature has taken away some of our authority in
this area," admits Hogo. In 1994 the district had considered reducing
passenger car traffic into airports. At the same time, it had proposed requiring
owners of sporting event centers and shopping centers to develop plans to
reduce vehicle trips into their locations, says Hogo. A cross-section of
business interests pressured the state legislature to block the latter
proposal; the legislative stone killed both birds.
Gary Honcoop, manager of the office
of air quality and transportation planning at the CARB, refuses to discuss what
other approaches to cleaning airport emissions might be explored, saying,
"There is a lot of sensitivity because of the airlines involved and some
of their concerns. I would hesitate to stir that process up by identifying too
much specificity at this point."
NASA, however, is developing new
engines that could reduce NOx by 70% by the middle of the next
decade. "We have a pretty good indication that [these levels] can be
achieved," says Richard Niedzwiecki, a senior engineer in aeronautics for
combustion and emissions research at NASA's Lewis Research Center in Cleveland,
Ohio. Such engines could be in commercial aircraft as early as 2008.
Nonetheless, global warming will
complicate further efforts to bring down emissions, says Niedzwiecki. To save
on CO2 emissions, he explains, aircraft
weight must be reduced. But reducing NOx requires engines with larger
combustion zones. Furthermore, higher operating temperatures reduce CO2emissions,
but raise NOx emissions.
"There is now talk of seeking
much more substantial CO2 reductions,
and we are putting a program together," says Niedzwiecki. He is
"cautiously optimistic" that both CO2 and NOx goals can be met, but the time frame
for doing so, he says, is 2010-2050.
More than 4 million gallons of glycols
were used for aircraft de-icing at 93 airports during 1989-1991, according to a
survey by the FAA. Glycols are the most voluminous water pollutants from
airports. As there are over 500 certified airports in the United States, the
actual amount emitted may be much higher.
During de-icing, the airlines mix
55% glycol and 45% water, heat the mixture to about 185° F, and spray the
planes down with it, says Miles Carter, manager of environmental services at
Denver International Airport. Without recapture efforts, 50-80% of the glycols
may end up in the local waterways, says Mark Williams, assistant environmental
program manager for the Maryland Aviation Administration. Forty-five of the 50
busiest airports in the United States are within 3 miles of a major waterway,
according to the NRDC report. Other chemicals besides glycols that are used at
airports may get into waterways, but information about these is sketchy. At
Kennedy Airport, there are two underground lakes of jet fuel, estimated to
contain 3-5 million and 6-9 million gallons, respectively, according to the
NRDC report. The New York State Department of Environmental Conservation has
ordered the airport to remove the fuel.
But glycols receive the most
attention. Ethylene glycol is both more effective and more toxic than propylene
glycol. The lethal dose for humans of ethylene glycol is a little over three
ounces, according to a report prepared for the EPA. Less can damage kidneys.
Propylene glycol is relatively innocuous. However, both ethylene glycol and
propylene glycol consume high levels of oxygen during decomposition, according
to the Airports Council International, a trade group in Washington, DC. This
can deplete waterways of oxygen and kill fish.
The NRDC complains that regulations
for disposal of de-icing chemicals lack teeth. The stormwater pollution
prevention plans (SWPPPs) required of states under the Clean Water Act should
greatly reduce contaminated stormwater discharges from airports if implemented
as required, according to the NRDC report. But, the report continues, "It
is not clear when, or if, the plans will be inspected by a regulatory
agency." In addition, "SWPPPs must be made available only to
regulatory agencies, not the public," which impedes the ability of citizen
groups to ensure proper implementation. Says Bennett, "I find that
impossible to believe, but compliance is up to . . . the states."
Furthermore, only those airports
using an annual average of 100,000 gallons or more of de-icing fluid will be
required to monitor or sample, according to the NRDC. These represent either 4
or 10% of airports nationwide, according to figures by the American Association
of Airport Executives and the FAA, respectively. Bennett defends the air
transportation providers, saying that the NRDC has provided no evidence that
airports are not meeting established regulatory standards. He adds that,
although these contituencies have the right to participate in development of
regulatory standards, they have no authority to make a final determination of
what those standards are.
A small number of airports are very
successfully recapturing glycols following use. According to the Airports
Council International, 14 of 48 airports surveyed had containment systems for
recapturing used glycols. Six airports prepared them to be recycled for other
uses.
At Maryland's Baltimore/Washington
International Airport, an estimated 25% of glycols are collected following
de-icing. That doesn't mean that 75% find their way into the waters. Some of
that amount evaporates or goes into the ground, where it decomposes in about
4-20 days, says Williams. The FAA is developing a new model to try to determine
how much glycol actually gets into the water.
Baltimore/Washington uses two
de-icing pads near the end of the runways to retrieve the glycols. The pads,
big parking areas, are sloped to shunt de-icing fluids from beneath the plane,
along with any precipitation that lands there, down one drain. Stormwater
collected elsewhere goes down another drain. Baltimore/Washington also uses "glycol
recovery vehicles," vacuum sweepers that "look sort of like street
sweepers, that suck up the glycol and any liquid on the pavement," says
Barbara Grey, manager of environmental plans and programs for the Maryland
Aviation Administration. The glycol is piped to a huge tank, and then released
very slowly over months to the sewage treatment plant.
At the Denver airport, which was
designed to optimize collection of glycols, 65-70% of the fluid is recaptured,
says Carter. These glycols are concentrated to a relatively high 25% on
average, depending on the duration and nature of the precipitation.
Recyclers increase the concentration
to as high as 99.5%. "We recycle it for coal companies, some paint
manufacturers, and General Motors," says Carter. But in the United States,
recycled glycols are never used for de-icing, unlike in Europe. "The
American manufacturers of glycol have convinced the U.S. airlines that it is a
liability to use recycled glycol, although the same airlines use it in Europe
all the time," says Carter.
A technological fix that could
render de-icing chemicals partially obsolete is the use of infrared rays to
heat the exterior of the plane. In such a process, immediately before takeoff
the plane would pull into a hangar-like structure outfitted with the infrared
energy process units and park there for approximately six minutes while the
de-icing takes place.
"I'm really thrilled about
it," says Robert Stone, manager of Buffalo Niagara International Airport,
where the technology is about to be tested. Capital costs for the process,
which are less than $2 million, are far less than the cost of systems to
recapture de-icing fluids, which can range into the tens of millions. Six
planes can be de-iced for $100-200 worth of gas and electricity, while a single
de-icing with glycols can cost $2,500.
The projected doubling of
passenger air traffic within the United States in the next 20 years, as well as
the rapid growth of the U.S. population (which every 11 years adds the
equivalent population of another California), virtually ensures that the
environmental impact of airports will increase unless strong mitigation
measures are taken. It is likely that population pressure will lead to greater
numbers of people living near airports, even if not within the 65-DNL contour.
Even as planes become quieter, increasing numbers will ply the skies, exposing
people within the flight pattern to more, if perhaps softer, booms. The 25-30
year lifetime of airplanes will keep large numbers of today's polluting engines
aloft long after technological solutions begin to make significantly cleaner
engines available. And technological advances in the area of de-icing have been
slow coming, potentially allowing toxic chemicals to continue to be released
into groundwater. Says Feith, "I think that none of us, even here at EPA,
have given substantial thought as to what are potential solutions to the
problem of airport pollution."
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