Methodology

Data Sources
The data on air quality throughout the United States were obtained from the U.S. Environmental Protection Agency’s Air Quality System (AQS), formerly called Aerometric Information Retrieval System (AIRS) database. The American Lung Association contracted with Dr. Allen S. Lefohn, A.S.L. & Associates, Helena, Montana, to characterize the hourly averaged ozone concentration information and the 24-hour averaged PM2.5 concentration information for the 3-year period for 2004-2006 for each monitoring site. Design values for the annual PM2.5 concentrations by county were collected from data previously summarized by the U.S. Environmental Protection Agency (EPA) and were used as received from the EPA on October 31, 2007 in personal correspondence from Mr. Mark Schmidt, EPA.

Ozone Data Analysis
The 2004, 2005, and 2006 AQS 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 the 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 reflect the normal conditions. The highest 8-hour daily maximum concentration in each county for 2004, 2005, and 2006, 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 the EPA based on the EPA Air Quality Index. The Air Quality Index then in place used the 1997 National Ambient Air Quality Standard set at 0.084 ppm. Those ranges are:

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.

Short-term Particle Pollution Data Analysis
A.S.L. & Associates identified the maximum daily 24-hour AQS PM2.5 concentration for each county in 2004, 2005, and 2006 with monitoring information. 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 maximum of the daily PM2.5 concentration was within the ranges identified by EPA based on the EPA Air Quality Index, adjusted by the American Lung Association as discussed below:

from 0.0 µg/m3 to 15.4 µg/m3 Good (Green)
from 15.5 µg/m3 to 35.0 µg/m3 Moderate (Yellow)
from 35.1 µg/m3 to 65.4 µg/m3 Unhealthy for Sensitive Groups (Orange)
from 65.5 µg/m3 to 150.4 µg/m3 Unhealthy (Red)
from 150.5 µg/m3 to 250.4 µg/m3 Very Unhealthy (Purple)
greater than or equal to 250.5 µg/m3 Hazardous (Maroon)

On September 21, 2006, the EPA announced a revised 24-hour National Ambient Air Quality standard for PM2.5, changing the standard from 65 µg/m3 to 35 µg/m3. The EPA has not yet announced changes to the Air Quality Index based on the new standard. However, the Lung Association adjusted the level of the category “Unhealthy for Sensitive Groups” to include the new standard, making that category range from 35.1 µg/m3 to 65.4 µg/m3.

No data capture criteria were used to eliminate monitoring sites. All data were used in the analysis because it was the goal to identify the number of days that the maximum in each county of the daily AIRS PM2.5 concentration occurred within the defined ranges. Only 24-h averaged PM data were used. Included in the analysis are data collected using only FRM and FEM methods, which reported 24-h averaged data. As instructed by the Lung Association, A.S.L. & Associates included the exceptional and natural events that were identified in the database and identified for the Lung Association the dates and monitoring sites that experienced such events.

Following receipt of the above information, the American Lung Association identified the number of days each county, with at least one PM2.5 monitor, experienced air quality designated as orange, red, purple or maroon.

Description of County Grading System
Ozone and Short-term Particle Pollution (24-hour PM2.5)
The grades for ozone and short-term particle pollution (24-hour PM2.5) were based on a weighted average for each county calculated using the Air Quality Index as noted above. The number of orange days experienced by each county was assigned a factor of 1, red days a factor of 1.5, purple days a factor of 2 and maroon days a factor of 2.5. By multiplying the total number of days within each category by their assigned factor, a total was determined. Because the monitoring data were 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 defined Metropolitan Statistical Area. In 2006, the White House Office of Management and Budget published revised definitions for the nation’s Metropolitan Statistical Areas. Therefore, comparisons between MSAs of the State of the Air 2008 report and earlier State of the Air reports should be made with caution.

All counties with a weighted average of zero (corresponding to no exceedances 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 (corresponding to 1 to 2 orange days) received a "B." Counties receiving a "C" had only 3 to 6 days over the standard, including at most one red day, and 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 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 or maroon category. The number of days for an "F" grade was set to roughly correlate with the number of days that would place a county in nonattainment for the ozone standard. For short-term particle pollution, the number of days required for an F would roughly approximate a 99th percentile form of the PM2.5, a form the American Lung Association supports.

Grading System

Grade	Weighted Average	Approximate Number of Allowable Orange/Red/Purple/Maroon days
A	0.0	None
B	0.3 to 0.9	1 to 2 orange days with no red
C	1.0 to 2.0	3 to 6 days over the standard: 3 to 5 orange with no more than 1 red OR 6 orange with no red
D	2.1 to 3.2	7 to 9 days over the standard: 7 total (including up to 2 red) to 9 orange with no red
F	3.3 or higher	9 days or more over the standard: 10 orange days or 9 total including at least 1 or more red or purple

Weighted averages allow comparisons to be drawn based on severity of air pollution. For example, if one county had 9 orange days and 0 red days, it would earn a weighted average of 3.0 and a D grade. However, another county which had only 8 orange days, but also had 2 red days, which signify days with more serious air pollution, would receive an F. That second county would have a weighted average of 3.7.

Note that this system differs significantly from the methodology the EPA uses to determine violations of both the ozone standard and the 24-hour PM2.5. the EPA determines whether a county violates the standard based on the 4th maximum daily 8-hour ozone reading each year averaged over three years. Multiple days of unhealthy air beyond the highest four in each year are not considered. By contrast, the system used in this report recognizes when a community’s air quality repeatedly results in unhealthy air throughout the three years. Consequently, some counties will receive grades of “F” in this report showing repeated instances of unhealthy air, while still meeting the EPA’s 1997 ozone standard or the 1-hour ozone standard set in 1979. The EPA adopted a new ozone standard on March 12, 2008. This grading system has not been adjusted to reflect the new standard.

Year-round particle pollution (Annual PM2.5)
Since no comparable Air Quality Index exists for year-round particle pollution (annual PM2.5), the grading was based on the EPA’s determination of violations of the national ambient air quality standard for annual PM2.5 of 15 µg/m3, as reported October 31, 2007 in personal correspondence from Mark Schmidt, EPA. Counties that the EPA listed as being in attainment of the standard were given grades of “Pass.” Counties that the EPA listed as being in nonattainment were given grades of “Fail.” Where insufficient data existed for the EPA to determine attainmentor nonattainment, those counties received a grade of “Incomplete.” Counties were ranked by design value. Metropolitan areas were ranked by the design value among the counties in the Metropolitan Statistical Area as of 2006 as defined by the White House Office of Management and Budget. 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 the EPA to determine whether or not the air quality in a county meets the standard.

The Lung Association received critical assistance from members of the National Association of Clean Air Administrators, formerly known as the State and Territorial Air Pollution Control Administrators and the Association of Local Air Pollution Control Administrators. With their assistance, all state and local agencies were provided the opportunity to review and comment on the data in draft tabular form. The Lung Association reviewed all discrepancies with the agencies and, if needed, with Dr. Lefohn at A.S.L. and Associates. Questions about the annual PM design values were referred to Mr. Schmidt of the EPA, who reviewed and had final decision on those determinations. The American Lung Association wishes to express its continued appreciation to the state and local air directors and to Mr. Schmidt of the EPA for their willingness to assist in ensuring that the characterized data used in this report are correct.

Calculations of Populations-at-Risk
Presently county-specific measurements of the number of persons with chronic lung disease and other chronic conditions are not generally available. (The primary exception to this is asthma, as state-specific estimates for adult asthma are available through one national survey discussed below.) In order to assess the magnitude of lung disease and other chronic conditions at the state and county levels, we have employed a synthetic estimation technique originally developed by the U.S. Bureau of the Census. This method uses age-specific national estimates of self-reported lung disease and other conditions to project the prevalence of disease by county.

Population Estimates
The U.S. Census Bureau estimated data on the total population of each county in the United States for 2006. The Census Bureau also estimated the age-specific breakdown of the population by county.

Prevalence Estimates

Chronic Bronchitis, Emphysema, Pediatric Asthma and Cardiovascular Disease.
In 2006, the National Health Interview Survey (NHIS) estimated the nationwide annual prevalence of diagnosed chronic bronchitis at 9.5 million; the nationwide lifetime prevalence of emphysema was estimated at 4.1 million. The NHIS estimates the prevalence of diagnosed pediatric asthma to be over 6.8 million under age 18. The NHIS estimates the prevalence of cardiovascular disease (CV) at 74.6 million among adults age 18 years and over, which includes coronary heart disease, hypertension, stroke, angina pectoris and heart attack.

Due to the revision of the Health Interview Survey questionnaire, prevalence estimates from the American Lung Association State of the Air 2000 cannot be compared to later publications. Estimates for chronic bronchitis and emphysema can be compared to the State of the Air reports for 2001 through 2008. Furthermore, estimates for chronic bronchitis and emphysema cannot be summed since they represent different types of prevalence estimates.

Pediatric asthma prevalence estimates from this year’s report can only be compared to those in the State of the Air reports since 2004 and not the State of the Air reports from 2000 through 2003 due to a change to the National Health Interview Survey.

Local area prevalence of chronic bronchitis, emphysema, pediatric asthma and CV disease are estimated by applying age-specific national prevalence rates from the 2006 NHIS to age-specific county-level resident populations obtained from the U.S. Bureaus of the Census web site. Prevalence estimates for chronic bronchitis, emphysema and CV disease are calculated for those 18 to 44, 45 to 64 and 65+. The prevalence estimate for pediatric asthma is calculated for those under age 18.

Adult Asthma.
In 2006, the Behavioral Risk Factor Surveillance System (BRFSS) survey indicated that approximately 8.5% of adults residing in the United States reported currently having asthma. The information on adult asthma obtained from the Behavioral Risk Factor Surveillance System survey cannot be compared with pediatric asthma estimates that are derived from the National Health Interview Survey.

The prevalence estimate for adult asthma is calculated for those 18 to 44, 45 to 64 and 65+. Local area prevalence of adult asthma is estimated by applying age-specific state prevalence rates from the 2006 BRFSS to age-specific county-level resident populations obtained from the U.S. Bureaus of the Census web site.

Diabetes Estimates.
In 2006, the National Health Interview Survey estimated the nationwide lifetime prevalence of diabetes at 17.1 million. Local area prevalence of diabetes is estimated by applying age-specific national prevalence rates from the 2006 NHIS to age-specific county-level resident populations obtained from the U.S. Bureaus of the Census web site. Prevalence estimates for diabetes are calculated for those 18 to 44, 45 to 64 and 65+.

Limitations of Estimates.
Since the statistics presented by the NHIS and the BRFSS are based on a sample, they will differ (due to random sampling variability)
from figures that would be derived from a complete census, or case registry of people in the United States with these diseases. The results are also subject to reporting, non-response and processing errors. These types of errors are kept to a minimum by methods built into the survey.

Local estimates of chronic diseases are scaled in direct proportion to the base population of the county and its age distribution. No adjustments are made for other factors that may affect local prevalence (e.g. local prevalence of cigarette smokers or occupational exposures) since the health surveys that obtain such data are rarely conducted on the county level. Because the estimates do not account for geographic differences in the prevalence of chronic and acute diseases, the sum of the estimates for each of the counties in the United States may not exactly reflect the national estimate derived by the NHIS or state estimates derived by the BRFSS.

References

Irwin, R. Guide to Local Area Populations U.S. Bureau of the Census Technical Paper Number 39 (1972).

National Center for Health Statistics. Raw Data from the National Health Interview Survey, United States, 2006.

Calculations by the American Lung Association Research and Program Services Division using SPSS and SUDAAN software.

Centers for Disease Control and Prevention. Behavioral Risk Factor Surveillance System, 2006.

Population Estimates Branch, U.S. Bureau of the Census. County Resident Population
Estimates, by Age, Sex, and Race: July 1, 2006.

Office of Management and Budget. Update of Statistical Areas Definitions and Guidance on Their Uses. OMB Bulletin 07-01 December 18, 2006.