**12.1 ENVIRONMENTAL IMPACT OF AVIATION OPERATIONS**

**Pollution (Noise, air, soil)**

Space debris and micrometeoroids are a valid concern for human space
operations in earth orbits

Aviation activity is associated with a variety of aircraft emissions and
noise concerns that have an impact on global and local environment.
Locally, in the vicinity of the airport, noise is one of the most
commonly voiced concerns, and local emissions of concern are CO,
volatile organic hydrocarbons, and nitrogen oxides. The major water and
soil quality issues were related to fuel spills at the airport and
de-icing and anti-icing fluids and chemicals. Deicing chemicals
sometimes go into water supply.

Globally, the important atmospheric constituents of environmental
concerns are CO2 and water vapor, nitrogen oxides (No~x~), and sulfur
oxides. Most emissions come from aircraft at high cruising altitudes
(30,000 to 40,000 feet). CO2 has a 100-year atmosphere lifetime, and is
well mixed throughout the atmosphere. The CO2 from aviation operations
is indistinguishable from that from other sources. The nitrogen oxides,
sulfur oxides, water vapor and particles have a much shorter residence
time, and remain concentrated near the flight routes, mainly in the
northern mid latitudes where most of the world's air travel occurs.
However, the impact of these emissions is difficult to quantify. The
Intergovernmental Panel on Climactic Changes was established by the
United Nations and issued a report in 1999 outlining their best estimate
of the effects of aircraft emissions on the environment.

Aviation emissions account for approximately 3.5% of the human
contribution to global warming from fossil fuel use. This will probably
grow to 5-6% of the total effect by 2050.

Aviation contributes an estimated 2% of the emissions of CO2 from fossil
fuels, and this is expected to grow to 3% by 2050.

Emissions of No~x~ from jets are thought to have increased ozone levels
at cruising altitudes by 6% since the 1992, and could increase to 13% by
2050. The No~x~ emissions have a mixed effect of warming and cooling.
No~x~ destroys another greenhouse gas (methane), but No~x~ in itself is
a greenhouse gas. Ozone increases caused by nitrogen oxides may be
offset by aircraft water vapor emissions. The net effect is therefore
not certain.

The effects of aircraft No~x~, water vapor, and aerosol in combination
with CO2 could be two to four times the effect of the CO2 alone.

Worldwide, passenger traffic is expected to grow 5% annually at least to
2015. Fuel use is only projected to grow 3% per year due to fuel
efficiency improvements.

The earth's temperature could increase 1.6 degrees F by 2050, and the
aviation contribution to that is estimated to be 0.09 degrees.

Aircraft and engine technology improvements could increase fuel
efficiency by 20% by 2015, and 40-50% by 2050. In particular there is
work to reduce No~x~ emission by 70% during takeoffs and landings.

Operational improvements may decrease fuel burned in aviation activities
by 6-18%, with an additional 6-12% coming from air traffic management
improvements.

The overall expected improvements in technology are not expected to
completely offset the general increase in the numbers of flights and
aircraft operations in the next 50 years

Fuel dumping, or jettisoning of fuel in-flight is performed in
situations where the aircraft gross weights needs to be reduced in order
to permit a safe landing. Many aircraft take off with gross weights
above their designed landing weight. An emergency or diversion then
could necessitate landing prior to their flight plan, leading to having
to land over their gross weight. Fuel is then jettisoned in flight to
reduce the weight of the aircraft. Most of the fuel that is dumped turns
into vapor within a few minutes. If jettisoned above 5000 feet in above
freezing temperature calculations show that 98% will evaporate before
reaching the ground. The fuel vapors rapidly dissipate and diffuse. This
could contribute to photochemical oxidant pollution, smog. The portion
that remains in droplet form could lead to condemnation of water, and
possibly cause some local rain. When these droplets settle to the
ground, usually they are spread over a wide area, minimizing their
effect.

The contribution to this kind of vapor pollution is negligible when
compare to that from cars, trucks, and industrial sources. Since this
happens relatively rarely, fuel dumping does not have major
environmental implications.

A survey completed by the Government Accounting Office of the 50 busiest
commercial airports, accounting for 80% of air carrier operations in
1998 revealed that noise, water, and air quality were the top three
concerns. About 90% of the management of these airports thought that
balancing environmental concerns with airport operations was much more
or somewhat more difficult than it was in 1989.

Because 13 of these facilities were at or above capacity with another
four considered to be at capacity in the following 1-2 years, the
pollution concerns were only be compounded. Two thirds of these airports
were planning to build new or extend existing runways in the next ten
years. There was growth not only in airport operations and in air
travel, but travel to and from the airport.

Noise was considered the most serious concern for the airports. Issues
with nearby land use was their third biggest concern, which is directly
linked to the noise issue because of a federal mandate that noise above
a certain level to be incompatible with homes and school use of the
land. Considering the future, many of these managers consider air
quality to be their biggest concern.

The noise issue of reported greatest concern was that aircraft jet
engines are still too loud, even with the national standards for quiet
engines that has been implemented. This relates to the encroachment of
residential areas on the airport. Under federal land use rules, the
noise limits for residential and school building from aircraft operation
are 65 dB. Yet half of these busiest airports have between 1,000 and
25,000 people living within an area where sound levels reach 65 dB or
more. Many noise complaints are still received from outside of this
area. Most airports monitor noise levels daily. Noise abatement
procedures are required or encouraged, such as ground run-up limitations
or restrictions, preferential use of certain flight paths, and limits on
uses for certain runways.

Propylene glycol is the most used deicing or ant-icing chemical used
directly on aircraft. Ethylene glycol is the second most used. The
runways are increasingly being deiced with potassium acetate and other
glycols. Runoff from deicing operations is typically handled by vacuum
sweeper trucks, stormwater systems or deicing pads. Most of the airports
send the fluid to public-owned treatment facilities for disposal, or to
private contractors for off-site disposal.

Many airports rank in the top 10 industrial air pollution sources in
their cities. An EPA study found that aircraft emissions are potentially
significant increasing sources of air pollution in ten major cities. EPA
review of capacity expansion projects accounted for cancellations or
indefinitely postponed expansion projects in one fourth of these top 50
airports.

There are some estimates that 1% of smog is due to aviation operations,
and air operations account for up to 4% of CO2 and NO2 emissions.

There have been several ideas that have been suggested to decrease air
pollution concerns from aviation activities:

Increasing fuel efficiency and other aircraft engine improvements

decreasing taxiing, and, therefore ground aircraft emissions

by improving the timing and therefore the efficiency of departures

assigning aircraft to runways that minimize the time and distance on the
ground

shutting down one or more engines early

towing airfact between taxiways and gates

provide electricity and preconditioned air at the gates to reduce
aircraft fuel use.