1. The Weighted Average was derived by adding the three years of individual level data (2004-2006), multiplying the sums of each level by the assigned standard weights ( i.e. 1=orange, 1.5=red, 2.0=purple and 2.5=maroon) and calculating the average.
a. Asterisk (*) indicates incomplete monitoring data for all three years. Therefore, those counties are excluded from the grade analysis or received an Incomplete.
b. A dash (-) indicates that data on that particular pollutant is not collected in that county.
c. Grades are as follows: A=0.0, B=0.3-0.9, C=1.0-2.0, D=2.1-3.2, F=3.3+.
2. The Design Value is the calculated concentration of a pollutant based on the form of the National Ambient Air Quality Standard, and is used by EPA to determine whether the air quality in a county meets the standard. The source for the Design Values is EPA, communication from the Office of Air Quality Planning & Standards, Mark Schmidt, October 31, 2007.
More about Methodology.
State of the Air: 2008 
