Chemtrails: What’s the truth behind the conspiracy theory?

High humidity means that vapour trails can last for long periods and become thin layers of cirrus clouds, Met Office meteorologist Aidan McGivern told the BBC. Cirrus clouds are short, detached and hair-like and are found at high altitudes. It is unlikely that any of these purported chemicals in the clouds would even reach ground level because they are at such high altitudes, he said.