White Smoke trails behind Aircrafts (Contrails)

You must have encountered these white smoke trails (sometimes yellow) also called Contrails when looking above. I guess now, most of us have grown up and know the real reason behind these trails. But I have some real misconception regarding this thing and that is damn silly.

In my childhood, whenever I see these trails, I thought a rocket is launched and it is releasing smoke. Sometimes these trails appears like yellowish orange which appears to me like fire from rocket thrusters . Isn’t that silly?

To my surprise, I don’t see some flights releasing smoke which helps me to differentiate between a rocket and an airplane (I thought one that releases are rockets and that not are normal aircrafts). How dumb I was.

But what actually is this thing? Why only some jets release these trails? And why do these trails differ in their width (if you’d noticed)? So, let’s begin.

• The trails you are seeing is basically condensed form of water vapor (or moisture vapor) released with the exhaust gases during combustion of fuel. How do they condense? It is because airplanes fly at a very high altitude. And due to that much height, the temperature and vapor pressure (low vapor pressure implies little tendency to convert into gaseous state) is quite low compared to that of exhaust gases. As a result, due to this difference, the moisture vapors in exhaust gases condense and form a cloud like impression in the sky.
• The second factor is Humidity of the atmosphere in which the aircraft is flying. If the humidity( amount of water vapor present in air) is high, then the moisture will not be absorbed by the atmosphere and we can see that clearly. On the other hand, if the humidity is low, then that moisture will be absorbed by the atmosphere and the trails will no longer be visible for a long time. That also explains why some trails are narrow and thin as compared to other.
• The less common and rare factor is the Engine type. Sometimes, it also depends on the aircraft type. Because the byproduct of combustion i.e. carbon dioxide, Sulphur and nitrogen oxides, soot serves as a condensation site for water vapor. Now, since the engines are more efficient, the quality of combustion is good which can affect the contrails formation.

So, that’s how I’d cleared my misconception. Also, there is a single rocket launch pad in India which is Satish Dhawan space center in Sriharikota. How can I see that rocket launch (which is more than a 1000 km away from me)? And no space station launches couple of rockets in a single day if my childhood theory is assumed correct. Anyways, that’s why it’s called childhood days.