As the summer smog season begins, several sources can help you provide better coverage of this serious health and environmental issue. Regardless of the information source and its particular spin, keep in mind that many scientific studies show that significant health damage can occur at concentrations below the current standards for several air pollutants, including particulates and ozone.
On May 1, 2007, the American Lung Association released its latest annual report on ozone and particulate threats in many US cities and counties. ALA: Hallema Sharif Clyburn,  212-315-8727, or Janice Nolen,  202-785-3355 x222; release.  The findings are limited, since they cover only certain aspects of just two pollutants, but they do provide one snapshot of recent conditions, and they zoom in to the city and county level.
For 2003-2005, ALA found that ozone threats dropped in much of the country, but that particulate threats increased in much of the East. Overall, they conclude that about 136 million people (46% of the population) continue to live in a county that violates one of the existing standards that ALA tracked - ozone, and short- and long-term particulates - and that about 12% live in counties that violate all three. When covering these assessments, note that ALA does not combine the city or county grades for each category into one composite grade.
Another view on a few basic air pollutants is provided by EPA, which, using preliminary 2006 data, estimates that 103 million people live in counties that violate current standards for the handful of criteria air pollutants (with some counties violating multiple standards; for instance, 73 million people live in counties that violate the 8-hour ozone standard, and 66 million live in counties that violate the fine particulate (PM2.5) standard). The 103 million figure is down from 122 million for 2005, possibly because of both reduced emissions and variable weather.
- EPA: John Millett,  202-564-7842; April 30, 2007, press release  on preliminary data, including link to preliminary findings.
EPA also is estimating that the emitted quantities of many of the criteria pollutants dropped slightly from 2005 to 2006, though particulate matter is expected to remain unchanged, as are volatile organic compounds, which contribute to ozone formation. Keep in mind that the final numbers may be somewhat different from the preliminary estimates. EPA's final annual report using 2006 data is expected in August or September 2007 (see Air Trends ).
To check on daily conditions for the criteria pollutants in your area, including forecasts, see Air Quality Forecast Guidance  (eastern US),Experimental Air Quality Forecast Guidance  (all US), and AIRNow. 
Keep in mind that none of the sources mentioned above address hundreds of other important air pollutants, such as those covered by the Toxics Release Inventory or the National Air Toxics Assessment, or those otherwise designated as hazardous air pollutants.