How Green Is Flying? Aviation's Pollution Problem

Planes have long been blamed for greenhouse gas emissions and global warming. Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, and jet airliners emit carbon dioxide (CO2), the most understood greenhouse gas, as well as nitrogen oxides, contrails, and particulates. In 2018, global commercial operations generated 2.4% of all CO2 emissions, and emissions from planes rose by 32% between 2013 and 2018. While aviation emissions are rising rapidly, they represent less than 2-3% of global CO2 emissions, compared to road traffic, which accounts for around 10%. However, only a small percentage of the world flies frequently, and aviation emissions are expected to triple by 2050.

Planes' carbon emissions are rising rapidly

Aviation is a significant contributor to climate change, and emissions from planes are rising rapidly. Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, which has led to planes being blamed for greenhouse emissions and global warming. In 2018, global commercial operations generated 2.4% of all CO2 emissions, and this figure is expected to grow to 3.5% by 2030.

While fuel efficiency is gradually reducing emissions per passenger, it is not keeping up with the rapid increase in total passenger numbers, which are projected to double in the next 20 years. For example, between 1990 and 2019, passenger demand quadrupled, and freight demand increased by a similar amount. This has resulted in a 32% increase in emissions from planes between 2013 and 2018.

The carbon intensity of the fuel used in aviation has not changed, and standard jet fuel is still in use today. However, there are potential alternatives, such as e-kerosene, biofuels, and electrification, which could significantly reduce emissions from the sector. Additionally, zero-emissions aircraft, such as hydrogen or electric planes, could help decrease aviation emissions for shorter ranges. Nevertheless, these technologies require significant funding and are not expected to be widely available until the mid-2030s.

The impact of aviation emissions is not limited to CO2 alone. Aircraft engines also emit nitrogen oxides, water vapour, soot, sulfur aerosols, and water contrails, which have strong warming effects. These non-CO2 emissions contributed twice as much to global warming as aircraft CO2 in 2018 and were responsible for two-thirds of aviation's climate impact that year.

To reduce aviation's carbon footprint, individuals can choose to fly less, especially for business purposes, as demonstrated by the ease of remote work during the COVID-19 pandemic. When flying is necessary, choosing newer aircraft, flying economy, and selecting airlines with lower emissions can help minimise the environmental impact.

Aviation's non-CO2 effects

Aviation is a significant contributor to climate change. While carbon dioxide (CO2) emissions are the most significant and best-understood contributor, other non-CO2 emissions and factors also have a substantial impact on global warming.

Nitrogen Oxides (NOx)

Nitrogen oxides, including nitric oxide and nitrogen dioxide, are emitted by aircraft engines during fossil fuel combustion. At altitudes of 8 to 13 km (26,000 to 43,000 ft), NOx emissions favor the formation of ozone (O3) in the upper troposphere, resulting in greater concentrations of O3 than surface NOx emissions. These elevated O3 concentrations have a more substantial global warming effect.

Contrails and Cloud Formation

Contrails, or condensation trails, are formed when water vapor is released from jet engines at high altitudes under specific humidity conditions. This water vapor can condense into exhaust carbon particles, atmospheric aerosols, and, in sufficiently humid conditions, crystals that form clouds. Contrails and cloud formation can have a warming effect, trapping outgoing heat and contributing to global warming. The impact of contrails varies depending on their persistence, location, time of day, weather conditions, and the combined effect of multiple contrails.

Other Non-CO2 Emissions

In addition to NOx and contrails, aviation also emits other substances with warming effects, including soot, sulfur oxides (SOx), carbon monoxide (CO), unburned hydrocarbons (UHC), aerosols, and traces of hydroxyl compounds (-OH). These emissions contribute to the overall climate impact of the aviation industry.

Airport Operations

Airport ground operations and infrastructure also contribute to non-CO2 effects. Airports' extensive use and handling of jet fuel, lubricants, and chemicals can result in significant water pollution. Deicing fluids used during cold weather can pollute nearby water sources through surface runoff. Additionally, airport construction and aircraft manufacturing generate greenhouse gas emissions that further contribute to the industry's environmental impact.

Alternatives to jet fuel

Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, raising environmental concerns over their global effects and their effects on local air quality. The aviation industry hopes to cut down on its climate impact by using new fuels. These alternatives, often called sustainable aviation fuels (SAFs), are made from a wide range of sources and can be used by existing planes. SAFs are derived from renewable sources and fall into two main categories: biofuels and synthetic electrofuels.

Biofuels come from a range of biological sources, including waste like used cooking oils, agricultural residues, or landfill trash. However, some crop-based biofuels can produce more carbon dioxide emissions than fossil fuels, especially those made from palm oil, as growing this crop can decimate rainforests.

Synthetic electrofuels, or e-fuels, are made with carbon sucked from the air via direct air capture, and their manufacturing facilities are powered by renewable electricity. These synthetic fuels can reduce emissions by nearly 100% compared to fossil fuels. However, producing e-fuels is currently expensive and inefficient, and they are not yet produced at a commercial scale.

Other alternative jet fuels include FT-SPK, created through the gasification of biomass, and ATJ-SPK, created via biochemical or thermochemical sugar and starch crop conversion. FT-SPK provides 85-95% greenhouse gas savings compared to conventional jet fuel, while ATJ-SPK can save up to 75% of CO2 emissions.

While alternative fuels offer a promising future for the aviation industry, their actual impact will depend on various factors, and the challenge of cost and limited supply must be addressed.

The impact of airports

Airports have a significant impact on the environment, contributing to water and air pollution and generating greenhouse gas emissions.

Firstly, airports are significant generators of water pollution due to their extensive use and handling of jet fuel, lubricants, and other chemicals. These substances can spill and contaminate water sources if not properly managed. Deicing fluids, for example, are often used in cold weather to deice aircraft and paved surfaces. These fluids contain chemicals such as ethylene glycol or propylene glycol, which can pollute water if they are not properly contained and cleaned up.

Secondly, airports contribute to air pollution through the emissions produced by aircraft engines and ground vehicles. Aircraft engines emit carbon dioxide (CO2), nitrogen oxides, contrails, and particulates from fossil fuel combustion, which have both local and global effects on air quality and climate change. CO2 is the most well-understood greenhouse gas, contributing to the warming of the planet. Nitrogen oxides emitted at high altitudes can also lead to the formation of ozone, which has a greater global warming effect.

Additionally, airport ground vehicles, such as those used by passengers and staff to access airports, as well as emissions from airport construction and aircraft manufacturing, further contribute to the overall greenhouse gas emissions associated with the aviation industry.

Reducing corporate travel

Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, which has raised environmental concerns over their global effects and their effects on local air quality. Jet airliners contribute to climate change by emitting carbon dioxide (CO2), the most understood greenhouse gas, and, with less scientific understanding, nitrogen oxides, contrails, and particulates. In 2018, global commercial operations generated 2.4% of all CO2 emissions, and this is projected to grow to 3.5% by 2030.

Corporate travel is a significant contributor to aviation emissions. Airlines have been catering to wealthier leisure travellers and those on business trips by offering more premium seating, such as first-class cabins. However, demand for corporate travel has been weakening due to economic uncertainty and reduced spending by companies.

To reduce corporate travel's environmental impact, companies can encourage employees to:

• Opt for video conferencing instead of in-person meetings, where possible.
• Choose more environmentally-friendly modes of transport, such as trains, coaches, or ferries, for shorter distances.
• Fly with airlines that use the newest aircraft possible, as these tend to be more fuel-efficient and produce fewer emissions.
• Book economy tickets instead of business or first class, as these emit fewer emissions per passenger.
• Avoid unnecessary stopovers and choose direct flights where possible, as taking off uses more fuel than cruising.
• Offset their carbon emissions by investing in carbon offsetting projects, such as tree-planting initiatives.

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