Particulates are killers.

Much publicity has been given to the potential health risks posed by buildings, particularly those with mechanical ventilation or air conditioning. There have been concerns over the possible effects of the vocs given off by the furnishings and finishes, of fungal spores shed from dirty ducting, of legionella distributed by wet cooling towers, of insufficient ventilation air, etc., etc. The list of concerns is a long one. But what about the effects on the building occupants of the air brought in from outside, the so-called 'fresh air'? Compared with when domestic coal fires and 'smoke stack' industries were prevalent, present-day pollution levels are low. Despite this though, researchers recently have begun to find startling evidence that outdoor air can be positively harmful to health and that the biggest threat is the fine particles which are semi permanently suspended in it. These don't just make people feel off-colour. They can kill.