EDIT: it turns out that my memory was faulty, the research was into light chains, which is related to inflammatory conditions (http://www.jni-journal.com/articl

EDIT: it turns out that my memory was faulty, the research was into light chains, which is related to inflammatory conditions (http://www.jni-journal.com/article/S0165-5728(09)00012-5/abstract http://www.jni-journal.com/article/S0165-5728(09)00012-5/abs...). The research on fine particles is this (http://link.springer.com/article/10.1186%2F1743-8977-7-35 http://link.springer.com/article/10.1186%2F1743-8977-7-35), which a friend gave me. Guess I read too much crap. Sorry! My wife was involved (Masters thesis) in some primary research into the causes of asthma / other allergies involving the respiratory system. It was experimental research (which involved lab mice, iirc), not statistical. Her results showed that fine particles of a certain size caused damage that would cause respiratory problems (i.e. asthma). Luckily in Europe at least there regulations are getting stronger over time; that's why we're all driving cars with catalytic converters and filters.