How Does an Aircraft’s Exhaust Gases Affect the Environment?

The Air Transport Action Group (ATAG) reported that in 2014, there had been 37.4 million flights scheduled that year– which is a little more than 100,000 flights up in the air each day.   

With so many planes in flight at any given time, one might wonder, “how does an aircraft’s exhaust gases affect the environment?” After all, planes do have powerful engines to generate the forward thrust necessary to get them flying in the first place.  

An aircraft’s exhaust gases contain CO2 emissions, and as environment scientists have pointed out, it’s these that have a greenhouse gas effect on our atmosphere, trapping in heat.

Carbon Emissions from Aircraft 

According to the ATAG, flights worldwide have produced 781 million tons of CO2 in 2015. While this is just about 12% of the world’s total CO2 emissions (compared to the 74% contributed by road transport), it’s still a significant amount. 

Furthermore, an aircraft in flight is releasing these greenhouse gases into the atmosphere, where it does even more damage. 

Because of air currents at high altitudes, aircraft exhaust spreads more throughout the earth. Compared to ground transport exhaust in the lower atmosphere, the colder, thinner air affects ATF chemical reactions differently as well.  

What’s in the Gases in Aircraft Exhaust? 

Modern-day aircrafts fly through the combustion of aviation turbine fuel– which is also known as ATF. This specific type of fuel is sort of similar to kerosene in some respects, but it’s a longer-chain compound. 

Longer-chain compounds are harder to burn completely. Much in the same way our body processes (i.e. burns) more complex carbohydrates (e.g. vegetables, fiber, pasta, etc.) than simple sugars (e.g. candy, soda, etc.), aircraft also have a hard time completely burning ATF. 

The result? When ATF goes through combustion, a lot of partially burned gas mixtures are also emitted through its exhaust. ATF emissions include carbon dioxide (CO2), nitrous oxide (NOx), water vapor (H2O), and sulfates.  

• Carbon Dioxide. Global warming experts have already established the damaged caused by CO2 on our environment. 

• Nitrous Oxide. Releasing these gases in higher altitudes results in an imbalance in ozone levels, also contributing to global warming. 

• Water Vapor. When water is dispersed in the upper atmosphere, the cold air condenses them into crystals, forming condensation trails or “contrails”. Sometimes these contrails evaporate, and sometimes they persist. And when they do, they can impact the environment and temperature in the ground below.

• Sulfates and other Particulate Matters (PM). Soot from aircraft exhaust absorbs heat, while sulfates radiate energy. In the upper atmosphere, the mix of these substances in aircraft exhaust has some effects on clouds. 

Is Anything Being Done About Aircraft Carbon Emissions? 

Luckily, ICAO, the United Nations-backed international civil aviation body has already recognized this issue.  

In a landmark historic accord, the ICAO has passing legislation regarding atmospheric pollution, convincing member countries to adopt new measures to use more alternative fuel sources, as well as enforce new technical and operational improvements to drastically cut down CO2 emissions. 

Sustainable biofuel– such as those derived from algae, jatropha, and camelina– have been identified as excellent candidates for helping achieve industry targets. Using these biomass alternatives, the industry can reduce the carbon footprint of aviation fuel by up to 80% over their full lifecycle. 

Industry experts suggest that if commercial aviation were to get 6% of its fuel supply from biofuel by 2020, this would reduce its overall carbon footprint by 5%. It’s a good start, and hopefully, it’s a measure that everyone in the industry can get behind sooner than later. 

(Special thanks to Arun Shankar, Krishna Kumar Subramanian, and ATAG.)