why some flights emits more smoke with white color?

Answer 1

No Smoke! They are called contrails(condensation trails)

Contrails are created in one of two ways:

1. First, the airplane's exhaust increases the amount of moisture in the air, which can push the water content of the air past saturation point. This causes condensation to occur, and the contrail to form.

Aviation fuel such as petrol/gasoline (piston engines) or paraffin/kerosene (jet engines) consists primarily of hydrocarbons. When the fuel is burned, the carbon combines with oxygen to form carbon dioxide; the hydrogen also combines with oxygen to form water, which emerges as steam in the exhaust. For every gallon of fuel burned, approximately one gallon of water is produced, in addition to the water already present as humidity in the air used to burn the fuel. At high altitudes this steam emerges into a cold environment, (as altitude increases, the atmospheric temperature drops) which lowers the temperature of the steam until it condenses into tiny water droplets and/or desublimates into ice. These millions of tiny water droplets and/or ice crystals form the contrails. The temperature drop (and therefore, time and distance) the steam needs to condense accounts for the contrail forming some way behind the aircraft's engines.

2. The wings of an airplane cause a drop in air pressure in the vicinity of the wing (this is partly what allows a plane to fly). This drop in air pressure brings with it a drop in temperature, which can cause water to condense out of the air and form a contrail.

Exhaust contrails tend to be more stable and long-lasting than wing-tip contrails, which are often disrupted by the aircraft's wake and are commonly very short-lived.

Answer 2

What we see are finely dispersed ice crystals from the exhaust water rather than "smoke" (which would be solid particles as remnants of burning, such as soot or dust).

Depends on the temperature of the air layer the plane travels through. Some environmentalists have suggested that planes ought to avoid the layers where massive ice plumes follow, in order to avoid additional cloud cover. The region where I live gets up to 10% cloud cover (light absorption) on clear days just from plane exhausts...

Answer 3

Smoke that's white isn't fully combusted! It means there is gasoline with the smoke. Smoke that's black is just dirty smoke. It's better to inhale black smoke coming from vehicles than white smoke, but it's best not to inhale at all! :D

Answer 4

All planes release smoke but we don't see it usually because the air is turbulent. We see the white smoke when the air is not turbulent.