Article: Effects of Aviation Emissions

Over 3 billion people, nearly half the global population, use the world’s airlines.  The air transport industry provides 56 million direct, indirect, and induced jobs worldwide, which is double the number of jobs only eight years ago. While aircraft carry only 0.5 percent of world trade shipments, that represents about 35 percent of the value of all world trade.  This productivity is achieved consuming just 2.2 percent of world energy.

Figure01

The reality is that aviation must develop if it is to continue to meet the needs of a growing economy and an expanding population. At the same time, aviation must be environmentally sustainable, operating harmoniously within the constraints imposed by the need for clean air and water, limited noise impacts, and a livable climate. 

It should be kept in mind that wide range of environmental regulations applies to airport activity and equipment. Aircraft engines have certification requirements for carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and smoke emissions. Ground access vehicles are subject to tailpipe emission standards, and ground support equipment (GSE) may be subject to nonroad engine standards. The composition of jet fuel, diesel fuel, and gasoline are all regulated to limit harmful emissions, ensure proper performance of engines and fuel systems, and avoid engine durability concerns.

The reduction in the level of sulfur in gasoline is justified by its known reduction in the efficiency of catalytic converters, which means these devices are less capable of removing emissions from exhaust gases. Thus, removing sulfur is a means of reducing other emissions of toxins from ground vehicle exhausts. Reduction of naphthalenes in fuel reduces the formation of carbonaceous particles that are potentially harmful, because they can cause erosion on turbine blades and form hot spots that can lead to premature engine failure. Many operational activities and equipment require permits.

Furthermore, the Federal Aviation Administration (FAA) must consider the air quality impact of actions it undertakes, licenses, or funds and determine that airport expansion plans conform to regional air quality plans.

The European Union (EU) passed a law in 2008 to require airlines to account for emissions for the entirety of any flight that takes off or lands at any airport in Europe, even if that flight began or ended as far away as Shanghai or San Francisco. Under the European system, airlines must show each year that they have bought a sufficient number of carbon permits to compensate for their emissions on those routes.

Figure02

Unfortunately, EU had no consultation whatsoever with the International Civil Aviation Organization (ICAO) while regulating international aviation emissions in and out of EU airspace.  Consequently, members of ICAD had strongly criticized EU efforts to include emissions under their Emissions Trading System (ETS).

At the same time, transportation officials from around the world in October 2013 reached a preliminary agreement to develop global rules by the end of the decade that would control airline emissions. The action by the ICAO represents the first major move toward industrywide rules to limit carbon pollution.

Under the resolution, the nations mainly agreed to develop a global system to control emissions by 2016 that would take effect at the beginning of the next decade. But there is no guarantee of a final deal, given the countries’ divergent priorities.

“ICAO has taken a significant step forward toward addressing aviation greenhouse gas emissions,” Anthony Foxx, the United States Transportation Secretary, said in a statement before the decision. The deal “Ensures that all airlines are treated fairly wherever they fly.”

But the agreement is also a blow for the EU.  During the general assembly of the United Nations Aviation Agency, a number of countries continued to reject EU Regulations, increasing pressure on the region to scale back or repeal one of its flagship environmental laws.

European negotiators sought explicit endorsement to levy carbon fees on international airlines using European airports for the length of their flights within European airspace. But the agreement said that any states operating a regional system to levy fees on international carriers should seek permission from other countries first.

The EU law is still in force. But European officials have already pared back the rules significantly and conceded that the original approach was unworkable because of the prospect of retaliatory trade measures.

At the same time the Obama administration proposed on 10 June 2015 to regulate aircraft emissions in much the same way as power plants, saying they are a threat to human health because they contain pollutants that help cause global warming.

Using its authority under The Clean Air Act, the Environmental Protection Agency (EPA) finding of endangerment to human health clears the way for possible US adoption of international emissions standards.  The ICAO has been working for several years on developing global aircraft emissions standards. Final agreement on those standards is expected in February of 2016.

The EPA is also issuing an Advance Notice of Proposed Rulemaking that provides information on the process for setting an international carbon dioxide (CO2) emissions standard for aircraft at the ICAO, and describes and seeks input on the potential use of section 231 of the Clean Air Act to adopt and implement the corresponding international aircraft engine CO2 emissions standard domestically.

The US transportation sector is a significant contributor to total US and global anthropogenic greenhouse gas (GHG) emissions. Aircraft remain the single largest GHG-emitting transportation source not yet subject to GHG standards in the US.  US aircraft emit:

  • 11 percent of GHG emissions from the transportation sector in the US;
  • 3 percent of total US GHG emissions;
  • 29 percent of GHG emissions from all aircraft globally; and
  • 0.5 percent of total global GHG emissions.

It is important to note that US regulations would apply only to large planes.  The EPA Administrator is proposing to find that GHG emissions from certain classes of engines used primarily in commercial aircraft contribute to the air pollution that causes climate change and endangers public health and welfare. Specifically, she proposes to find that GHG concentrations in the atmosphere endanger the public health and welfare of current and future generations within the meaning of section 231(a) of the Clean Air Act.

While negotiations on the standards are still underway, they aren’t expected to go into effect until 2020 or afterward, and possibly as late as 2025, say environmentalists following the matter.

Here is an interesting perspective based on the fact “You’re more likely to die from exposure to toxic pollutants in plane exhaust than in a plane crash,” a new study says. The good news is that nobody is disagreeing with the fact that airplane exhaust, like car exhaust, contains a variety of air pollutants, including sulfur dioxide (SO1) and nitrogen oxides (NOX).

In recent years, airplane crashes have killed about a thousand people annually, whereas the shocking news is that plane emissions kill about ten thousand people each year, researchers say.

According to the study leader, Steven Barrett, an aeronautic engineer at the Massachusetts Institute of Technology (MIT) in Cambridge – “We found that unregulated emissions from (Planes Flying) above 3,000 feet (914 meters) were responsible for most of the deaths.”

Earlier studies had assumed that people were harmed only by the emissions from planes while taking off and landing. The new research is the first to give a comprehensive estimate of the number of premature deaths from all airline emissions.  Globally, the team estimated that about 8,000 deaths a year result from pollution from planes at cruising altitude—about 35,000 feet (10,668 meters)—whereas about 2,000 deaths result from pollution emitted during takeoffs and landings.

Here is a fact.  When a plane flies at cruising altitude above the clouds, wind currents can whisk the pollution far away so that prevailing winds cause the pollution to fall from the sky about 6,000 miles (10,000 kilometers) to the east of the plane’s route.

The United States incurs about 450 deaths each year from airplane emissions—only about one-seventh the number of deaths that would be expected if the pollution fell straight to the ground from planes, the study said.

In India, on the other hand, there are an estimated 1,640 deaths per year from airplane emissions—about seven times more deaths than would be expected based on the number of flights that start or finish in the country.

Most of these deaths are caused not by flights over India but from emissions in Europe and North America at high altitude, which then blow across Asia, according to the study, published in the October issue of Environmental Science & Technology.

Here is another fact.  Airplane pollution deaths still represent a small share of the toll from all kinds of air pollution.  And the annual total death toll from air pollution is about a million, according to the United Nations Environment Programme.  More specifically, airplane-pollution deaths account for about a tenth of all air-pollution deaths with cross-border causes, said Junfeng Liu, an atmospheric chemist at Princeton University.  So airplane pollution could be an important focus for environmental regulations in the future.

Aircraft are not the only source of aviation emissions. Airport access and ground support vehicles typically burn fossil fuels and produce similar emissions. This includes traffic to and from the airport, shuttle buses and vans serving passengers, and GSE that services aircraft. Other common emissions sources at the airport include auxiliary power units (APU) providing electricity and air conditioning to aircraft parked at airport terminal gates, stationary airport power sources, and construction equipment operating on the airport.

Comparing aviation climate change emissions to other transportation modes, only some, but not all, GHG emissions, such as CO2, are directly related to fuel use, and most transportation modes use similar fuels. For that reason, energy intensity – the amount of energy consumed to transport one passenger one mile – is a useful metric for comparing greenhouse gas emissions among different transportation modes. For instance, Rail, at 2,750 BTU/passenger miles, has the lowest energy use per passenger mile among primary transport modes and transit buses the highest at 4,364 BTU/passenger miles. Aviation and automobiles have efficiencies between those two.

Figure03

Aviation stands out among transportation modes, however, in terms of improving fuel efficiency over the past decade. With automobiles at 3,496 BTU/passenger mile versus airlines at 3,505 BTU/passenger mile, between 2004 and 2012, auto energy intensity fell to 3,193 BTU/passenger mile, for an 8.8 percent improvement. For the same period, aviation energy intensity fell to 2,654 BTU/passenger mile, a 24.3 percent improvement and is now significantly lower than automobiles. These trends were confirmed in a recent study. Aviation is now approaching rail as the most energy efficient transportation mode based on energy intensity per passenger mile.

The level of aviation activity reflects the overall demand for worldwide travel and trade. Demand for travel services, both passenger travel and freight transportation, increased substantially in the last third of a century. Since 1980, gross domestic product (GDP) in the US has increased by 140 percent and air travel has increased by 134 percent.  Over the long term, it is expected that demand for air transportation will continue to grow. Current forecasts are for 2.3 percent per year growth of enplanements over the next two decades, resulting in 58 percent more passengers. As a result, growth of the aircraft fleet and expansion and further development of existing airports are expected. This also means that emissions from aviation activity are expected to increase unless the improvements in operational efficiency, sustainable alternative fuels, and associated low-emissions technologies can offset that growth.

While aviation activity is forecasted to grow, emissions are also dependent on other factors including:

  • Aircraft construction materials and technological sophistication – the lighter, more aerodynamic and technologically sophisticated an aircraft is, the less fuel it will use;
  • Aircraft operations – the less time an aircraft spends taxiing or idling on the ground and the more direct routing a flight can take, the less fuel it will use. Restricted or congested air space, adverse weather, congested airports, and inefficient ground operations can all result in increased emissions; and
  • Fuel composition – while they are needed in small quantities, the presence of sulfur and heavy or complex hydrocarbon molecules such as aromatic compounds create particle pollutants and reduce combustion efficiency.

Technology is expected to make a signif­icant contribution to the mid-and long-term reduction of GHG emissions and preservation of natural resources. Examples include new production methods, end-of-life recycling, new materials and advanced aerodynamic and engine design, such as open rotor and variable geared turbofan engines. Reinforced composites have already been introduced in the airframe structure. Safety and health risks of the implementation of composites in the airframe structure, insulation or aircraft secondary parts should be assessed. Special attention should be put on cases where these composite components are or can be damaged, fractured or exposed to heat. Links between aircraft emissions and potential climate change impacts are depicted below in a schematic Figure: 04:

Figure04

Aviation emissions affect both air quality and the global climate. Compared to other economic sectors, commercial aviation is a relatively small contributor to emissions of concern for both air quality and climate change. However, aviation emissions occur in the climatically sensitive upper troposphere and lower stratosphere where they may have a disproportionate impact on climate. They also occur at high altitudes where their impact may be felt at large distances away from where they are released.

Figure05

Concern regarding GHG emissions has been building worldwide. Total US greenhouse gas emissions have increased at an average annual rate of 0.4 percent since 1990. Transportation emissions in the US have increased about twice that fast and by 2012 accounted for about 28 percent of total US CO2 emissions, as illustrated in Figure: 05.

Aviation accounts for about 12 percent of transportation emissions, or 3.36 percent of total CO2 emissions in the US.  Similarly the latest global climate research indicates that aviation’s contribution to human-induced climate change is between 3.5 percent and 4.9 percent.  This share is forecast to increase to between 4.4 percent and 6.2 percent, by 2050 unless new technologies and policies are adopted to reduce aviation emissions. There remains a great deal of uncertainty in estimated impacts on climate change, which is being resolved through ongoing research efforts.

The climatic impacts of aviation emissions are quite complex and include direct climate effects from CO2 and water vapor emissions, the indirect effect on climate resulting from changes in the distributions and concentrations of ozone (O3) and methane (CH4) due to nitrogen oxides (NOx) emissions, the direct effects (and indirect effects on clouds) from emitted aerosols and aerosol precursors, and the climate effects associated with contrails and cirrus cloud formation.

Aviation is a complex and vital industry serving not only the US but also the entire world. It supplies tremendous economic benefits to those countries that embrace it. Its speed and accessibility are well suited to modern society as globalization, technology development, and just-in-time manufacturing transform the world. To maintain its central transportation role, aviation must ensure it can mitigate any environmental constraints that result from its operations.

There are features that distinguish aviation from other transportation modes and industries that must be factored into environmentally-motivated strategies. Aviation places a high premium on safety, which demands the incorporation of only proven and technically sound technologies to reduce environmental impacts. Aircraft are high cost and have a long life span, requiring long lead times for new technologies to be widely incorporated in the fleet. Airframe and engine manufacturers as well as airlines will need to invest the capital to build and operate aircraft with new technologies for aviation to realize the environmental and operational benefits. Airport infrastructure requires substantial planning and construction effort, as well as public and financial support. Such considerations increase the challenge of achieving the ambitious environmental and energy performance expectations.

In the meanwhile solar powered aircrafts which are emission free are making real progress. A solar-powered airplane consumes solar energy instead of traditional fossil fuels.  For instance, there is a long ranged experimental solar-powered aircraft project called Solar Impulse.  This is a privately financed project which is led by Swiss engineer and businessman André Borschberg and Swiss psychiatrist and aeronaut Bertrand Piccard, who co-piloted Breitling Orbiter 3, the first balloon to circle the world non-stop.  The ultimate objective of this project is to achieve the first circumnavigation of the Earth by a piloted fixed-wing aircraft using only solar power.

Figure06

This project has produced the following two prototypes which are single-seat monoplanes powered by photovoltaic cells and capable of taking off under their own power:

  • Solar Impulse 1: It was designed to remain airborne up to 36 hours.  It conducted its first test flight in December 2009. In July 2010, it flew an entire diurnal solar cycle, including nearly nine hours of night flying, in a 26-hour flight. Piccard and Borschberg completed successful solar-powered flights from Switzerland to Spain and then Morocco in 2012, and conducted a multi-stage flight across the United States in 2013; and
  • Solar Impulse 2:  It was completed in 2014 and it carries more solar cells and more powerful motors, among other improvements. In March 2015, Piccard and Borschberg began an attempt to circumnavigate the globe, departing from Abu Dhabi in the United Arab Emirates. The aircraft was scheduled to return to Abu Dhabi in August 2015, upon the completion of its multi-stage journey. By 1 June 2015, the plane had traversed Asia. On 3 July 2015, the plane completed the longest leg of its journey, from Japan to Hawaii. The distance represented 7,200 km (4,337 miles).  The record breaking flight took 117 hours with a maximum speed of 140 km (84.3 miles) per hour.  There were 17,200 solar cells built into the wing of Solar Pulse 2.
  • That was the largest non-stop solo flight in aviation history achieved without fuel, thanks to a solar-powered airplane.
  • During that leg, however, the aircraft’s batteries experienced thermal damage that is expected to take months to repair. The Solar Impulse team stated that they hope to resume the circumnavigation in April 2016.

80 engineers and technicians, with Borschberg at the helm, were involved in making the revolutionary Solar Impulse 2, applying novel and innovative solutions over a 12 year period.  In a time where airlines are rigorously seeking to reduce carbon emissions, this accomplishment is a significant step towards solar-powered airplanes and a greener future. Figure07

Here is some background – the first flight of a solar-powered aircraft took place on November 4, 1974, when the remotely controlled Sunrise II, designed by Robert J. Boucher of AstroFlight, Inc., flew following a launch from a catapult.

Following this event, AeroVironment took on a more ambitious project to design a human-piloted, solar-powered aircraft. The firm initially took the human-powered Gossamer Albatross II and scaled it down to three-quarters of its previous size for solar-powered flight with a human pilot controlling it. This was more easily done because in early 1980 the Gossamer Albatross had participated in a flight research program at NASA Dryden in a program conducted jointly by the Langley and Dryden research centers. Some of the flights were conducted using a small electric motor for power.

One encouraging trend relating to the future of solar energy is that many of the world’s greatest innovators are choosing to focus their talents and funds on improving alternative energy technology. Many award schemes — funded by various governments around the world — focus on providing solar power economically, and on a large scale.  This may lead to building solar-powered aircrafts with the potential alternatives to some present technologies, complementing current satellites and traditional airplanes.

Resources:

  1. Federal Aviation Administration: Aviation Emissions, Impacts, and Mitigation – A Primer;
  2. The New York Times: UN Group Moves to Develop Global Airlines Emission Rules;
  3. National Geographic:  Plane Exhaust Kills More People than Plane Crashes;
  4. Wikipedia: Solar Impulse;
  5. A Bright Future for Solar-Powered Airplanes;
  6. NASA: NASA Armstrong Fact Sheet – Solar-Powered Research; and
  7. Wise GEEK: What is the future of Solar Energy.