About the Cover

The display featured on the cover of this year's report provides an overall look at the status of ambient air quality trends for the six criteria pollutants over the past ten years. The bar graph shows, for each pollutant, the percentage of Metropolitan Statistical Areas (MSAs) in the last decade that have a statistically significant upward trend (the red portion of the bars); the percentage of MSAs that have a statistically significant downward trend (the green portion); and the percentage that have no significant trend (the gray portion). The small percentage of upward trends and the relative abundance of downward trends shows that air quality continues to improve in many of our nation's largest metropolitan areas. Additional information on trends in MSAs as well as the data contributing to this graphical display are contained in Chapter 6 of this report.