evidence: Some think malign forces are spraying the population with dangerous chemicals - so-called chemtrails - for purposes that are neither entirely clear nor consistent. [...] Initially, believers claimed sprays containing a toxic metal, barium, were being used to either pacify or reduce populations. [...] Chemtrail social media groups also often contain anti-vaccine posts and promote climate change denialism, feeding off an increase in conspiracy thinking during the Covid-19 pandemic, and the rise of the QAnon conspiracy theory during the Trump presidency.