Conspiracy theories can be stubborn, particularly in the echo chamber of the internet.
One persistent belief in some quarters is that the government — or business, perhaps — is deploying a fleet of jet aircraft to spray chemicals into the sky to control the population, food supply or other things.
As evidence, they point to what they call “chemtrails,” which are more commonly known as contrails, or condensation trails, produced at high altitudes as water vapor in jet engine exhaust condenses and freezes.
Adding fuel to the chemtrails theory is the fact that there are a few legitimate reasons for atmospheric spraying — “seeding” clouds to make rain, for example — and in recent years there has been some research on the idea of spraying chemicals as a potential way to fight global warming.
But now, scientists have become more organized in their efforts to shoot down the idea, conducting a peer-reviewed study in Environmental Research Letters that debunks chemtrails supporters’ claims.
The goal, the researchers say, is not so much to change the minds of hard-core believers, but to provide a rebuttal — the kind that would show up in a Google search — to persuade other people to steer clear of this idea.
Steven J. Davis, a climate scientist at the University of California, Irvine, said he had the idea for the study after a conversation with a salesman at a mattress store.
When the man found out what he did for a living, Dr. Davis said, “he had very serious questions about what we were going to do about the chemtrails problem.”
Dr. Davis said that when he got home, he searched the internet for peer-reviewed studies on the conspiracy theory, but found none.
The theory has been popularized on websites that display photographs of contrails but are described instead as chemtrails that persist in the atmosphere and contain harmful chemicals like strontium, barium and aluminum.
One of my favorite conspiracy theories to debate is “chemtrails.” The factual explanations behind the puffy white lines are so fabulously simple, you’ve got to marvel at those who harbor this preposterous notion. Entertain no fear, intelligent reader, as this conspiracy can only be held by the least scientific among us. To argue with chembelievers is to feel both frustration and bewilderment manifest.
You’ll hear the battle cry of the Chemtrailers: “Wake up! Look up!” soliciting you to abandon your ability to research for the blind acceptance of anecdotal opinion. We live in a world where information is so readily accessible for anyone who chooses to pursue it. The challenge comes in vetting sources, and this seems to be the trap in to which Chemtrailers fall. They want so badly to be right about being sprayed, they will use any source available that serves their confirmation bias.
Contrails, as they’re known by the scientifically literate among us, are quite simply explained. In fact, NASA does quite a good job of expounding it:
“Contrails are clouds formed when water vapor condenses and freezes around small particles (aerosols) that exist in aircraft exhaust. Some of that water vapor comes from the air around the plane; and, some is added by the exhaust of the aircraft. The exhaust of an aircraft contains both gas (vapor) and solid particles. Both of these are important in the formation of contrails. Some elements of the exhaust gasses are not involved in contrail formation but do constitute air pollution. Emissions include carbon dioxide, water vapor, nitrogen oxides (NOx), carbon monoxide, hydrocarbons such as methane, sulfates (SOx), and soot and metal particles.” 
Now the fun part…
“THERE’S CHEMIKILLS IN MY AIR.”
The quintessential Chemtrailer will claim that there are a host of chemicals being sprayed on us. In my experience, the most common particulates mentioned are aluminum, strontium, and barium. If these were being littered upon us in such volume as to cause detriment to our health, they would be easily detectable in soil and air samples yet, not surprisingly, no proof has been offered from any laboratory to date. Ask the conspiracy theorists to provide one; they can’t and they won’t.
“CONTRAILS DISSIPATE, BUT CHEMTRAILS DON’T.”
Some of the conspiracy theorists don’t want to seem as crazy and so they’ll justify their position by saying that chemtrails stay in the sky for hours while contrails dissipate quickly.