The death rays that guard life

Longtime readers know of my favourite nerdy subgenre: the in-depth profile of stuff our modern world runs on. Sometimes, that stuff is invisible. Like the air we breathe, and ultraviolet light that we can use to disinfect it. This profile ends with a thought-provoking question: We transformed public health by doing everything we can to guarantee clean water. We have the means to do the same with air. So how come – even after the coronavirus pandemic – clean air isn’t as universal and expected as clean water?