I love in-depth evaluations like these. There are many people who want to question the status quo, just as there are many people who want to defend it, but discussions with data behind them are so much more compelling.<p>This discussion leaves open questions about how much the size of particulate emissions matter, how much of each size becomes airborne versus simply falling to the ground, et cetera. In other words, this makes for an excellent starting point for someone else to do some more research and improve the picture. That can't be said of most discussions.