Every U.S. resident is at elevated risk of cancer from certain toxic substances in outdoor air, and about one-quarter of all residents are possibly at risk for noncancer health effects, according to EPA's update of the National-Scale Air Toxics Assessment (NATA) released March 11, 2011.
- NATA. 
But hold off on making definitive or absolute statements. The report, though a marked improvement in some ways from its predecessor, still has numerous significant limitations. For instance, the agency notes that, since the findings are based on 2005 data, risk could conceivably be less since a number of toxics-reducing regulations have been implemented since then.
On the other hand, the agency still hasn't made a formal risk estimate for diesel particulate matter, and the available information suggests this one substance alone may be one of the most threatening toxics of all 188 covered in NATA, and would increase the current total cancer risk estimate many-fold all by itself. In addition, the agency is just beginning to account for toxics that form in the atmosphere after precursors are emitted. The very few airborne toxics for which this has been done have jumped to the top of the risk list, in part because half or more of their ambient total is now estimated to come through this so-called secondary process.
Adding to the risk uncertainty is the fact that about one-quarter of the toxics that are supposed to be addressed in NATA haven't been included in the final risk estimates because of uncertainties caused by various factors. And thousands of toxics aren't covered at all by NATA. For the ones that are, only outdoor air threats are addressed, not indoor air threats or pathways such as skin, digestive, or fetal exposures.
Despite all these limitations, many state and local officials are finding NATA to be a useful tool. After your detailed review of the report – which includes maps that present the summary findings at a scale that makes it relatively easy to begin to assess currently estimated impacts for particular audience areas -- check with local environmental health and air pollution control officials to see what new takeaway information they're gleaning from this latest report, and what forthcoming actions are in the works. One starting point is:
EPA says it's trying to close the gap between the date of the data used and the year in which the next report is released. The next update, based on 2008 data, is scheduled to be unveiled in 2012, though some critics are skeptical this accelerated release schedule will hold.