|
|
DESCRIPTION OF METHODOLOGY
Statistical Methodology: The Air Quality Data
The data on air quality throughout the United States were obtained from the U.S. Environmental Protection Agency’s Aerometric Information Retrieval System (AIRS) database. The American Lung Association contracted with A.S.L. & Associates, Helena, Montana, to characterize the hourly averaged ozone concentration information for the 3-year period for 1999-2001. The 1999, 2000, and 2001 AIRS hourly ozone data were used to calculate the daily 8-hour maximum concentration for each ozone-monitoring site. The data were considered for a 3-year period for the same reason that EPA uses 3 years of data to determine compliance with the ozone: to prevent a situation in any single year, where anomalies of weather or other factors create air pollution levels, which inaccurately reflects the normal conditions. The highest 8-hour daily maximum concentration in each county for 1999, 2000, and 2001, based on the EPA-defined ozone season, was identified.
Using these results, A.S.L. & Associates prepared a table by county that summarized, for each of the 3 years, the number of days the ozone level was within the ranges identified by EPA based on the EPA Air Quality Index:
|
0.000 – 0.064 ppm |
Good (Green) |
|
0.065 – 0.084 ppm |
Moderate (Yellow) |
|
0.085 – 0.104 ppm |
Unhealthy for Sensitive Groups (Orange) |
|
0.105 – 0.124 ppm |
Unhealthy (Red) |
|
0.125 – 0.374 ppm |
Very Unhealthy (Purple) |
No data capture criteria were used to eliminate monitoring sites. All data within the ozone season were used in the analysis because it was the goal to identify the number of days that 8-hour daily maximum concentrations occurred within the defined ranges.
Following receipt of the above information, the American Lung Association identified the number of days each county with at least one ozone monitor experienced air quality designated as orange, red, or purple.
Description of County Grading System
A weighted average was used to determine the grade of each county. The number of orange days experienced
by each county was assigned a factor of 1; red days were assigned a factor of 1.5 and purple days were assigned a factor of 2. By multiplying the total number of days within each category by their assigned factor, a total was determined. Because the monitoring data was collected over a three-year period, the total was divided by three to determine the weighted average. Each county’s grade was determined using the weighted average. Counties were ranked by weighted average. Metropolitan areas were ranked by the highest weighted average among the counties in the Census Bureau-defined Metropolitan Statistical Area. All counties with a weighted average of zero (corresponding to no exceedences of the 8-hour standard over the three year period) were given a grade of A. Counties with a weighted average of 0.3 to 0.9 (generally corresponding to 1 to 2 orange days) received a B. Counties receiving a C had only 3 to 6 days over the standard, typically including at most one red day, scored a weighted average of 1.0 to 2.0. Counties received a D if they had a weighted average of 2.1 to 3.2, which meant they had generally 7 to 9 days over the standard. Counties with weighted averages of 3.3 or higher (corresponding to approximately the 8-hour standard) received an F. These counties generally had at least 10 orange days or 9 days over the standard with at least one or more days in the red or purple category.
|
|
|
