I noticed this news story about the UK Liberal Democrat party proposing in their manifesto for the forthcoming General Election in a few weeks time to introduce a ban on the sale of diesel cars and small vans. Also mentioned in the article is that they propose to legalise cannabis and use it as a new tax revenue stream.
At first sight that doesn't look particularly inconsistent, cracking down on pollution and a relaxed attitude to cannabis use are long-established left-liberal hobbyhorses. However the intention behind banning diesel cars is in large part a desire to protect the public from exposure to PM2.5 fine particulate matter. The legalisation of cannabis by a government would mean that it effectively approves of the idea of exposing a section of the public to far greater amounts of PM2.5 than they would experience from air pollution. According to Steven Milloy, smoking a marijuana joint could result in 18,000 times as much exposure to PM2.5 as a person breathing outdoor air for an hour: