Are there chemicals in jet exhaust?

Answer 1

Yes, there are chemicals in jet exhaust.

Jet fuel is very similar to kerosene, and when it burns, the main products of combustion are carbon dioxide and water in the gas phase. Because it is very cold at the altitude where jets fly and since the amount of water vapor produced over any given amount of time greatly exceeds the amount of gaseous water the cold, thin air can hold, it condenses almost immediately, and that is what constitutes the contrail that looks like a long, thin cloud behind a flying jet.

The next most abundant class of chemicals in jet exhaust are oxides of nitrogen. There are a number of nitrogen oxide species such as NO2, N2O2, N2O, N2O5 and a few others. Collectively, these species are called NOx's since they all have that same general formula. Thus, for the compound NO2, x=2, and for the compound N2O, x=½. Jet fuel consists almost entirely of hydrocarbon molecules; therefore it contains very little nitrogen, which would be present as nitrogen-containing organic molecules. Almost all of the NOx present in jet exhaust is formed when the nitrogen in air is heated to very high temperatures in the presence of oxygen. The same thing occurs in an automobile piston engine, albeit to a lesser degree since gasoline and diesel piston engines operate at much lower temperatures than jet engines.

Jet fuel most likely also contains a small amount of sulfur as does gasoline and diesel fuel. Like nitrogen, any sulfur would exist as sulfur-containing organic molecules, and it would be present in the exhaust as various oxides of sulfur. As with nitrogen oxides, the oxides of sulfur have the generic chemical formula SOx. Diesel fuel contains more sulfur compounds than gasoline or jet fuel, and the EPA has set limits on the maximum amount of sulfur diesel fuel may contain.

Both NOx and SOx compounds are harmful because they react with water to form acids. NOx and SOx compounds are the ones most responsible for acid rain. Carbon dioxide also dissolves in water to form carbonic acid, however carbonic acid is much weaker than nitric, nitrous, sulfuric, and sulfurous acids, and it is a non-oxidizing acid. There is also some evidence that certain NOx's destroy ozone in the ozone layer.

I have heard or read about some of the conspiracy theories surrounding the contrails created by jet aircraft. Some people are convinced chemicals that perform certain functions are added to jet fuel. Others believe that the contrails are not water vapor, but a chemical or mixture of chemicals sprayed from the back of jets. I have heard first hand from more than one person that these chemicals are able to control the weather; by either causing it to rain or preventing it from raining. Others believe or also believe that the chemicals eventually fall to earth and allow the government to control people's thoughts or behaviours. I'm sure others are convinced these chemicals have other deleterious effects.

It is impossible to prove absolutely that something does NOT have the effect someone claims it has. This is called proving the negative. The most convincing way to "prove" that something does not have the specific effect someone claims it has is by using statistics. For example, that is how pharmaceutical companies "prove" that a new drug does not cause cancer or have other serious health consequences. The drug is given to a large number of rats or rabbits or monkeys, etc., usually in doses much higher than any human would be prescribed, and the incidence of cancer or other negative effects in the test group is compared to a "control" group of the same species of animal with the same age profile that are treated the same way and fed the same diet, but without the drug being tested.

A certain fraction of any large enough group of mammals will eventually develop cancer and other serious health problems regardless of their diet. Even if there is not a higher incidence of cancer in the test animals compared to the control group, it doesn't prove absolutely that the drug doesn't cause cancer. The only conclusion that can be logically made from such an experiment is that the probability of the drug causing cancer is less than x%, where x depends on the number of test subjects and on the normal cancer rate in that species of animal.

As a professional Ph.D. Scientist, I assure anyone reading this that the contrails created from high-flying jet aircraft only contain condensed water vapor, oxides of nitrogen, and possibly very low levels of sulfur oxides. However, it is very difficult or impossible to convince the people who believe jet contrails contain additional chemicals intentionally added to jet fuel that such a notion is ridiculous. The believers will claim that anyone who denies this is part of the conspiracy. All I can do is hope that this country improves the quality and quantity of education in the sciences.