Contrails or chemtrails?

When I look in the sky I sometimes see contrails – white lines behind airplanes. A web page by the Center for Science Education at the University Center for Atmospheric Research succinctly explains:

“The white streaks you see coming off high-flying jet airplanes are called contrails, which is short for condensation trail. Contrails are clouds that form when water vapor condenses and freezes around small particles (aerosols) in aircraft exhaust. The water vapor comes from the air around the plane and the exhaust of the aircraft. These contrails can become human-made cirrus clouds. Contrails last longer when there is a greater amount of water in the air; when all of the water in the clouds evaporates the contrail disappears. There are three types of contrails: short-lived, persistent non-spreading, and persistent spreading.”

Here in Boise at jet aircraft altitudes the humidity usually is low, and most contrails are short-lived. At the Metabunk web site there is an article by Mick West from October 6, 2016 discussing Why were there contrails today, but not yesterday? It’s the weather!

What are chemtrails? A Wikipedia article titled Chemtrail Conspiracy Theory begins:

“The chemtrail conspiracy theory posits the erroneous belief that long-lasting condensation trails are ‘chemtrails’ consisting of chemicals or biological agents left in the sky by high-flying aircraft, sprayed for nefarious purposes undisclosed to the general public. Believers in this conspiracy theory say that while normal contrails dissipate relatively quickly, contrails that linger must contain additional substances. Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management, weather modification, psychological manipulation, human population control, or biological or chemical warfare, and that the trails are causing respiratory illnesses and other health problems.”

The conspiracy is called a Secret Large-scale Atmospheric Program (SLAP). There is a serious  article by Christine Shearer, Mick West, Ken Caldeira and Steven J. Davis in IOP Science Environmental Research Letters on August 10, 2016 titled Quantifying expert consensus against the existence of a secret, large-scale atmospheric spraying program. Experts on both contrails (49) and atmospheric deposition (28) replied to surveys. Just one deposition expert had ever seen evidence of SLAP – the other 76 said no. There is a less technical brief article about this one by Sabrina Stierwalt in Scientific American on September 22, 2018 titled What are chemtrails made of?

A web page on Chemtrails at Rational Wiki shows a doctored image of a control panel from an alleged chemtrail plane. Another article by Dan Evon at Snopes on June 7, 2017 titled Did President Trump tour a chemtrail plane? said no, that plane just had water ballast tanks for test flights – and the original article was at a satirical web site.

Images of contrails from twin engine and four engine jet planes both came from Wikimedia Commons.