Planes' Air Pollution: Understanding The Impact Of Aviation Emissions

Aviation is a significant contributor to global climate change and air pollution. The burning of fossil fuels by aircraft releases CO2 emissions and has strong warming non-CO2 effects due to nitrogen oxides, vapour trails, and cloud formation. These non-CO2 effects contribute twice as much to global warming as aircraft CO2 and were responsible for two-thirds of aviation's climate impact in 2018. Aviation emissions have been growing faster than any other mode of transport, with a projected doubling by 2050. Aircraft ground and low-altitude operations produce emissions that impact local air quality, and airports experience elevated levels of ultrafine particulate matter (UFP) and adverse health effects. To reduce pollution, airplanes can use clean fuels, and zero-emissions aircraft, such as electric planes, can help decrease emissions for shorter ranges.

Jet fuel combustion

The combustion of jet fuel is a significant contributor to air pollution and climate change. When jet fuel burns, it produces carbon dioxide (CO2) as well as non-CO2 emissions, including nitrogen oxides (NOx), soot, water vapour, and sulfate aerosols. These emissions have strong warming effects due to the formation of vapour trails and clouds at high altitudes. The non-CO2 emissions from jet fuel combustion have been found to contribute twice as much to global warming as aircraft CO2 emissions.

Jet fuels with high aromatics and naphthalene concentrations increase soot formation, leading to persistent contrail cirrus. To reduce these harmful emissions, several strategies can be employed. One approach is to perform hydrotreating on fossil jet fuels to lower the aromatics and naphthalene content. This method can be implemented without incurring significant costs and has the potential to significantly reduce non-CO2 effects.

Another strategy to mitigate the environmental impact of jet fuel combustion is to utilise sustainable biofuels blended with kerosene jet fuel. Biofuels have a significantly lower lifecycle greenhouse gas assessment than conventional petroleum-based jet fuel. They also help reduce soot content, water vapour, and sulfates in the exhaust, thereby decreasing the formation of contrails. Additionally, reducing the sulfur content of kerosene jet fuel and implementing engine design changes can further lower exhaust particulate emissions.

The use of clean fuels, such as e-kerosene, is also a potential solution to reduce air pollution from jet fuel combustion. While e-fuels require large amounts of renewable energy, they offer the possibility of significantly reducing emissions in the aviation sector. Furthermore, transitioning to more efficient aircraft designs and technologies can enhance energy efficiency, reducing the carbon intensity of air travel. However, it is important to note that the demand for air travel is expected to increase, posing challenges in maintaining improvements in energy efficiency and transitioning to low-carbon fuels.

The health effects of jet fuel combustion products have been a growing concern, particularly for populations living near large airports. Studies have shown that exposure to airport particles can induce inflammatory responses, DNA damage, and increase the risk of cardiovascular disease. More comprehensive research is needed to fully understand the toxicological mechanisms and health risks associated with jet fuel combustion products.

Non-CO2 emissions

Aviation is a significant contributor to climate change and air pollution. While burning fossil fuels releases CO2 emissions, it also has a strong warming effect due to non-CO2 emissions. These non-CO2 emissions, such as nitrogen oxides (NOx), soot, water vapour, and sulfate aerosols, interact with the atmosphere and influence the climate in various ways and across different timescales. This complexity makes their impact challenging to calculate.

To address non-CO2 emissions, airplanes can adopt cleaner fuels to reduce pollutants. Jet fuels with high aromatics and naphthalene concentrations increase soot formation and persistent contrails. By reducing the aromatics content in fossil jet fuel to 8-10%, non-CO2 effects can be significantly lowered without incurring significant costs. Additionally, rerouting flights to avoid Ice Super Saturated Regions (ISSR) and flying at lower altitudes can help minimise contrail formation.

The aviation sector faces challenges in decarbonisation due to the difficulty in reducing non-CO2 emissions. These emissions have a more complex impact on the climate, influenced by factors such as location, season, and time of day. While improvements in fuel economy and air traffic control can help, the most effective solution remains flying less. This can be achieved by choosing more sustainable modes of transportation, such as trains, or opting for destinations reachable by less climate-intensive means.

Contrails

The formation of contrails is influenced by the altitude at which aircraft operate and the interaction of emissions with the atmosphere. Nitrogen oxides (NOx), soot, water vapour, and sulfate aerosols are among the non-CO2 emissions produced by burning jet fuel. While some of these emissions have a cooling effect, the overall impact of contrails is warming. The ice crystals in contrail clouds trap heat, contributing to the warming of the upper atmosphere.

To mitigate the climate impact of contrails, several strategies can be employed. Cleaner jet fuels with low aromatics and low sulfur content can help reduce contrail formation and air pollution. New engine designs, such as lean combustion engines, can also decrease particle emissions, especially soot, which is a key contributor to contrail formation. Additionally, rerouting flights to avoid Ice Super-Saturated Regions (ISSR) and flying at lower altitudes can help prevent contrail formation. For example, rerouting a small percentage of flights in Japan reduced the warming effect of contrails by 60%.

While reducing contrail formation is challenging, addressing this hidden aspect of aviation's environmental impact is crucial. The inclusion of non-CO2 emissions in climate legislation and regulations is essential to driving change and mitigating the broader consequences of aviation on the climate and human health.

Fuel alternatives

Aviation is a significant contributor to global climate change and air pollution. The burning of jet fuel releases CO2 and non-CO2 emissions, including nitrogen oxides, soot, water vapour, and sulfate aerosols. The aviation sector is responsible for a large amount of fossil fuel combustion, which is the primary cause of this issue.

To reduce air pollution, the use of clean fuels is essential to decrease the amount of pollutants released into the atmosphere. One way to achieve this is by reducing the aromatics and naphthalene content in jet fuel through a process called hydrotreating. Lowering the aromatics content to 8-10% can significantly reduce non-CO2 effects without incurring significant costs.

Various alternative fuels have been proposed and tested for aviation, with the goal of reducing emissions and mitigating the industry's environmental impact. Here are some of the notable fuel alternatives:

• Sustainable Aviation Fuel (SAF): SAF is a safe alternative to traditional jet fuel, with almost identical chemical properties. It can be produced from non-petroleum-based renewable feedstocks such as food waste, yard waste, woody biomass, and fats/greases/oils. SAF has the potential to reduce emissions by up to 80%, with a 100% reduction being possible in the future. It is compatible with existing aircraft and infrastructure, providing flexibility and a seamless transition.
• Hydrogen (H2): Hydrogen is an attractive alternative aviation fuel due to its high energy content and lack of CO2 emissions during combustion. Hydrogen-powered aircraft could significantly reduce aviation emissions, but they require significant funding to become operational by the mid-2030s.
• Electrofuels: These fuels are produced from electricity through electrolysis of water, using captured carbon or nitrogen. Examples include Fischer-Tropsch kerosene, methane, methanol, hydrogen, ammonia, and n-octane.
• Liquefied Natural Gas (LNG): LNG has been studied as a potential alternative aviation fuel, with methane as its main energy carrier. However, challenges remain in operating LCH4 aircraft, particularly in the design and construction of LCH4 storage tanks and supply chain infrastructure.
• Ammonia (NH3): Ammonia, due to its high hydrogen content and lack of carbon atoms, is being considered as a potential aviation fuel. It can be used in low blending or as a dual fuel solution in modified aircraft engines and fuel cells.
• E-fuels: E-fuels, such as power-to-liquid, have the potential to be a source of zero or lower carbon alternative fuels. E-kerosene, in particular, can be sustainably scaled up to reduce the climate impact of aviation. However, they require vast amounts of renewable energy, and their environmental effectiveness depends on the source of CO2 used in their production.

Air quality near airports

Aviation is a significant contributor to climate change and air pollution. The burning of fossil fuels by aircraft releases CO2 and non-CO2 emissions, including nitrogen oxides (NOx), soot, water vapour, and sulfate aerosols. These emissions interact with the atmosphere, leading to both short-term and long-term effects on the climate.

Commercial airport activities can negatively impact the air quality in nearby areas, and millions of people live close to major airports, particularly in the United States. Studies have consistently shown elevated levels of ultrafine particulate matter (UFP) and particulate matter under 2.5 microns in diameter (PM2.5) near airports. However, it is challenging to make broad generalizations due to variations in airport operations, geography, and meteorology.

The composition of aviation fuel plays a crucial role in determining the amount of UFP emitted by aircraft. A recent study estimated that using 100% hydrotreated jet fuel with low sulphur and aromatics content could reduce UFP emissions by up to 70%, significantly improving air quality and reducing adverse health impacts. To address the issue of air pollution near airports, measures such as banning further expansion of airport infrastructure, introducing flight caps, and promoting alternative modes of transport like rail are recommended.

While zero-emissions aircraft, such as hydrogen or electric planes, offer a promising solution for reducing aviation emissions, they require significant funding and are not expected to be operational until the mid-2030s. In the short term, flying less is the most effective way to reduce emissions. This can be achieved by choosing more sustainable modes of transport, changing destinations to favour less climate-intensive options, and opting for teleconferencing instead of business travel.

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