As a professional aviator with 2,500 hours of flight time throughout our national aerospace system, and possessing a background in 
aerospace engineering and physics, I understand how and why some people without proper training in these disciplines might bite off on the chemtrail conspiracy crap. Nevertheless, I never cease to be amazed at how they can turn a blind eye to rock-solid information and persist in their beliefs.
When I say the chemtrail crap is crap, I mean just that: It’s crap.
Here’s what’s real: The chemical equation for stoichiometric combustion of a hydrocarbon in oxygen is given as follows:
That’s a contrail, ladies and gentlemen. You ignite a hydrocarbon in air. It 
combines with oxygen, producing carbon dioxide and water. The x and y denote the elemental fractions. The z just means the combustion occurs in an excess of oxygen.
fuel + oxygen –> carbon dioxide + water
It’s that simple.
As for “chemtrails,” I’ll keep that one simple, too. Chemtrails are a ridiculous, brain-dead myth. The very idea violates the laws of physics and biology. I’ve seen 
thousands of photos and videos of supposed “chemtrails” online, not one of which has ever appeared to be even remotely more than a plain old contrail, composed of water vapor precipitating into droplets or ice crystals in the presence of cold, humid air.
Contrails were observed long before World War II. Whether they disappear rapidly, slowly, persist, or foster additional condensation from the 
air around it is determined by the temperature, relative humidity, and density altitude of the air around it. If the air is too warm, contrails will not form. If the air is too dry or thin, they will not persist. When the surrounding air is more humid or dense, however, they can persist for hours. If the surrounding air is humid enough, contrails will cause additional precipitation, leading to the growth of clouds.
Contrails are so predictable, in fact, that during World War II, more than 70 years ago, the military’s weather forecasters would 
publish daily tables of time vs altitude for the aircrews, indicating where contrails were most likely to form. Allied bombers used this information to steer clear of those altitudes where contrails would form and give away their positions, making them far more visible to ground forces than if they weren’t producing contrails.
The criss-cross pattern of contrails occurs when numerous aircraft fly over the same ground track while the air mass moves. You can 
replicate this with a friend, two pencils, and a sheet of paper. Start drawing lines, one per second, then slowly move the paper beneath the lines. Draw your lines stationary relative to the desk, not the paper. Your pencils are “flying” over the same location on the “ground” while the moving paper represents the moving air mass. Result: cross-hatch. In fact, you can tell the general direction of upper-level winds by noting which direction parallel contrails go from sharp to fuzzy. Fuzzy are older. Therefore, they’re downwind.
The idea that spraying chemicals seven miles high would have any effect on the ground is absolutely ludicrous. Even with some of the most 
potent chemicals available, crop-dusters must still fly within a few feet of the crops. If they don’t, the chemicals disperse in even the mildest of air currents. Even if you allowed that aircraft swapped out half their fuel load in favor of toxic or mind-altering chemicals, you’re still dealing with the fact you’re spraying them from an altitude 3,000 times higher than required for cropdusters. As 
linear dispersion is proportional to the square of the altitude, however, you’re not talking about diluting the mix by a factor of 3,000, but by a factor of 9,000,000. That’s 9 MILLION times more diluted than a cropduster. Even if you were spraying pure botulism toxin, the world’s most potent toxin known to mankind, the concentration when it reached the ground would be so incredibly diluted that it would have no affect on either people or animals below!
Meanwhile, the increase in respiratory ailments is due to a number of factors, including the release of man-made xenohormones and other chemicals into our environment, primarily in the form of pesticides, herbicides, fungicides, pollution, and toxins found in a wide variety of industrial pollutants and man-made home furnishings, such as carpet and manufactured building materials. I’m sure the addition of fluoride into the water supply hasn’t helped things, any more than does chlorine, which is in the same family as fluoride. We know for a fact other things also cause problems, and that humans are much better off breathing fresh air, drinking fresh water and eating wholesome, organic foods.
The idea of chemtrails, however, is scientifically and logistically impossible, thoroughly debunked a thousand times over.
It’s absurd beyond the extreme, and only blithering idiots persist in such beliefs in the face of all known scientific fact to the contrary.
Nay… We’re dangerously polluting our environment and living spaces, all right, but we certainly don’t need to entertain the myth of chemtrails in the process. Fortunately, a number of aviation professionals have stepped up to set the record straight, such as this post found on Facebook:
Update (Dec 2, 2015): Another blitheringly idiotic post on Facebook claims “Conspiracy Theorists Vindicated: US Senate Reports Chemtrails Are Real and are Killing…”
Well, no. Here’s a copy of the photographed report, all 746 pages of it. No mention of chemtrails, there.
And here’s a copy of the searchable text of the report. Still no mention of chemtrails, much less anything about “killing,” with the sole exception of this sentence:
6. Dynamic effects:
(c) Cold thunderstorm downdrafts, either killing local convec-
tion or sotting off new convection cells elsewhere.
Update (August 20, 2018): I came across Phil Plaite’s,”Chemtrails conspiracy theory gets put to the ultimate test.” Rather good!
For the sake of argument, let’s use his severely gross lack of logic to point out just how incredibly and mindbogglingly stupid these ass hats really are:
