Here's something that might float your boat. This comes from a private organization than the government, who was against the claims of safe air (the way I understood it).
"The Environmental Protection Agency, along with the New York City Department of Public Health and others, have released
test results for only a few of the better known toxins, such as
asbestos, radiation, carbon monoxide, and bacterial/infectious materials. They have
ignored most of the components of the smoke and toxins bound to
dust particles. When they say the air is "safe," they mean that the chemicals they tested for fall within limits they consider acceptable for the general population. However, it should be emphasized that these "acceptable limits" for hazardous levels of substances are meant to apply to healthy adults, not to children, elderly, or infirm persons."
What this tells me is that the long/short term effects are acceptable, though certainly not the ideal. There must have been some other reason why precautionary masks weren't thrown out to the masses.
http://www.immuneweb.org/911/pr/100801.html