Methodology

The Air Quality Data

Description of County Grading System

Calculations of Populations-at-Risk

The Air Quality Data

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 2008-2010 for each monitoring site.

Design values for the annual PM2.5 concentrations by county for the period 2008 - 2010 were downloaded on September 24, 2011 from EPA’s website.

Ozone Data Analysis

The 2008, 2009, and 2010 AQS hourly ozone data were used to calculate the daily 8-hour maximum concentration for each ozone-monitoring site. The hourly averaged ozone data were downloaded on June 28, 2011. The data were considered for a 3-year period for the same reason that EPA uses three years of data to determine compliance with the ozone standard: 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 2008, 2009, and 2010, based on the EPA-defined ozone season, was identified.

The current national ambient air quality standard for ozone is 0.075 ppm measured over eight hours. EPA’s Air Quality Index reflects the 0.075 ppm standard. A.S.L. & Associates prepared a table by county that summarized, for each of the three years, the number of days the ozone level was within the ranges identified by EPA based on the EPA Air Quality Index:

8-hour Ozone ConcentrationAir Quality Index Levels

0.000 – 0.059 ppm

Good (Green)

0.060 – 0.075 ppm

Moderate (Yellow)

0.076 – 0.095 ppm

Unhealthy for Sensitive Groups (Orange)

0.096 – 0.115 ppm

Unhealthy (Red)

0.116 – 0.374 ppm

Very Unhealthy (Purple)

>0.374 ppm

Hazardous (Maroon)


The goal of this report was to identify the number of days that 8-hour daily maximum concentrations occurred within the defined ranges, not just those days that would fall under the requirements for attaining the national ambient air quality standards. Therefore, no data capture criteria were applied to eliminate monitoring sites or to require a number of valid days for the ozone season. All valid days of data within the ozone season were used in the analysis. However, for computing an 8-hour average, at least 75 percent of the hourly concentrations (i.e., 6-8 hours) had to be available for the 8-hour period. In addition, an 8-hour daily maximum average was identified if valid 8-hour averages were available for at least 75 percent of possible hours in the day (i.e., at least 18 of the possible 24 8-hour averages). Because the EPA includes days with inadequate data if the standard value is exceeded, our data capture methodology may result at times in underestimations of the number of 8-hour averages within the higher concentration ranges. However, our experience is that underestimates are infrequent.

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 (Unhealthy for Sensitive Groups), red (Unhealthy), or purple (Very Unhealthy).

Short-term Particle Pollution Data Analysis

A.S.L. & Associates identified the maximum daily 24-hour AQS PM2.5 concentration for each county in 2008, 2009, and 2010 with monitoring information. The 24-hour PM2.5 data were downloaded on August 1, 2011. In addition, hourly averaged PM2.5 concentration data were characterized into 24-hour average PM2.5 values by the EPA and provided to A.S.L. & Associates. 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:

24-hour PM 2.5 ConcentrationAir Quality Index Levels

0.0 µg/m3 to 15.4 µg/m3

Good (Green)

15.5 µg/m3 to 35.0 µg/m3

Moderate (Yellow)

35.1 µg/m3 to 65.4 µg/m3

Unhealthy for Sensitive Groups (Orange)

65.5 µg/m3 to 150.4 µg/m3

Unhealthy (Red)

150.5 µg/m3 to 250.4 µg/m3

Very Unhealthy (Purple)

greater than or equal to 250.5 µg/m3

Hazardous (Maroon)


In 2006, the EPA revised the 24-hour National Ambient Air Quality standard for PM2.5, changing the standard to 35 µg/m3 from 65 µg/m3. As of December 2011, the EPA had not announced changes to the Air Quality Index based on that standard. The Lung Association adjusted the level of the category “Unhealthy for Sensitive Groups” to reflect the 2006 standard, making that category range from 35.1 µg/m3 to 65.4 µg/m3.

The goal of this report was to identify the number of days that the maximum in each county of the daily PM2.5 concentration occurred within the defined ranges, not just those days that would fall under the requirements for attaining the national ambient air quality standards. Therefore, no data capture criteria were used to eliminate monitoring sites. Both 24-hour averaged PM data, as well as hourly averaged PM data averaged over 24 hours were used. Included in the analysis are data collected using only FRM and FEM methods, which reported hourly and 24-hour 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. Some data have been flagged by the state or local air pollution control agency to indicate that they had raised issues with EPA about those data.

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 (Unhealthy for Sensitive Groups), red (Unhealthy), purple (Very Unhealthy) or maroon (Hazardous).

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. To determine the weighted average, the Lung Association followed these steps:

  • First, assigned weighting factors to each category of the Air Quality Index. The number of orange days experienced by each county received 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. This allowed days where the air pollution levels were higher to receive greater weight.
  • Next, multiplied the total number of days within each category by their assigned factor, then summed all the categories to calculate a total.
  • Finally, divided the total by three to determine the weighted average, since the monitoring data were collected over a three-year period.

The weighted average determined each county’s grades for ozone and 24-hour PM2.5.

  • All counties with a weighted average of zero (corresponding to no exceedances of the standard over the three-year period) were given a grade of “A.”
  • For ozone, an “F” grade was set to generally correlate with the number of unhealthy air days that would place a county in nonattainment for the ozone standard.
  • For short-term particle pollution, fewer unhealthy air days are required for an F than for nonattainment under the PM2.5 standard. The national air quality standard is set to allow two percent of the days during the three years to exceed 35 µg/m3 (called a “98th percentile” form) before violating the standard. That would be roughly 21 unhealthy days in three years. The grading used in this report would allow only about one percent of the days to be over 35 µg/m3 (called a “99th percentile” form) of the PM2.5. The American Lung Association supports using the tighter limits in a 99th percentile form as a more appropriate standard that is intended to protect the public from short-term spikes in pollution.
Grading System
GradeWeighted AverageApproximate 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, purple or maroon


Weighted averages allow comparisons to be drawn based on severity of air pollution. For example, if one county had nine orange days and no red days, it would earn a weighted average of 3.0 and a D grade. However, another county which had only eight orange days but also two red days, which signify days with more serious air pollution, would receive a F. That second county would have a weighted average of 3.7.

Note that this system differs significantly from the methodology EPA uses to determine violations of both the ozone and the 24-hour PM2.5 standards. 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 EPA’s 2008 ozone standard. The American Lung Association’s position is that the evidence shows that the 2008 ozone standard fails to protect public health.

Counties were ranked by weighted average. Metropolitan areas were ranked by the highest weighted average among the counties within a given Metropolitan Statistical Area as of 2009 as defined by the White House Office of Management and Budget (OMB).

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 EPA’s determination of the national ambient air quality standard for annual PM2.5 of 15 µg/m3. Counties that EPA listed as being at or below 15.0 µg/m3 were given grades of “Pass.” Counties EPA listed as being at or above 15.1 µg/m3 were given grades of “Fail.” Where insufficient data existed for EPA to determine a design value, those counties received a grade of “Incomplete.”

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 or not the air quality in a county meets the standard. Counties were ranked by design value. Metropolitan areas were ranked by the highest design value among the counties within a given Metropolitan Statistical Area as of 2009 as defined by the OMB.

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 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 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 conditions are not generally available. In order to assess the magnitude of chronic conditions at the state and county levels, we have employed a synthetic estimation technique originally developed by the U.S. Census Bureau. This method uses age-specific national and state estimates of self-reported conditions to project disease prevalence to the county level. The primary exception to this is poverty, for which estimates are available at the county level.

Population Estimates

Total population for each county was obtained from U.S. Census Bureau summary files of the 2010 decennial census data, which included age- and gender-specific breakdowns.

Poverty estimates came from the Census Bureau’s Small Area Income and Poverty Estimates (SAIPE) program. The program does not use direct counts or estimates from sample surveys, as these methods would not provide sufficient data for all counties. Instead, a model based on estimates of income or poverty from the Annual Social and Economic Supplement (ASEC) to the Current Population Survey (CPS) is used to develop estimates for all states and counties.

Prevalence Estimates

Chronic Bronchitis, Emphysema and Cardiovascular Disease Estimates. In 2010, the National Health Interview Survey (NHIS) estimated the nationwide annual prevalence of diagnosed chronic bronchitis at 9.9 million, the nationwide lifetime prevalence of diagnosed emphysema at 4.3 million, and the nationwide lifetime prevalence of diagnosed cardiovascular disease at 74.7 million. Estimates for chronic bronchitis and emphysema should not be combined as they represent different types of prevalence estimates. Cardiovascular disease includes coronary heart disease, hypertension, stroke and heart failure.

Local area prevalence of chronic bronchitis, emphysema, and cardiovascular disease are estimated by applying age-specific national prevalence rates from the 2010 NHIS to age-specific county-level resident populations obtained from the U.S. Census Bureau web site. Prevalence estimates for chronic bronchitis, emphysema, and cardiovascular disease are calculated for those aged 18-44 years, 45-64 years and 65 years and older.

Asthma and Diabetes. In 2010, the Behavioral Risk Factor Surveillance System (BRFSS) survey indicated that approximately 8.6 percent of adults residing in the United States and 9.1 percent of children from twenty-nine states and Washington, D.C. reported currently having asthma. The BRFSS indicated that 9.2 percent of adults in the United States had ever been diagnosed with diabetes in 2010.

The prevalence estimate for pediatric asthma is calculated for those younger than 18 years; adult asthma and diabetes is calculated for those aged 18-44 years, 45-64 years and 65 years and older. Local area prevalence of pediatric asthma is estimated by applying the most recent state prevalence rates, or if none are available, the national rate from the BRFSS to pediatric county-level resident populations obtained from the U.S. Census Bureau web site. Pediatric asthma data from the 2010 BRFSS were available for thirty-two states and Washington D.C., five states1 from 2009, three states2 from 2008, and one state each3 for 2007 and 2006. National data was used for the eight states4 that had no data available since 2006. Local area prevalence of adult asthma and diabetes is estimated by applying age-specific state prevalence rates from the 2010 BRFSS to age-specific county-level resident populations obtained from the U.S. Census Bureau web site.

Limitations of Estimates. Since the statistics presented by the NHIS, BRFSS and SAIPE 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 U.S. 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.

Additionally, a major limitation of both surveys is that the information collected represents self-reports of medically diagnosed conditions, which may underestimate disease prevalence since not all individuals with these conditions have been properly diagnosed. However, the NHIS is the best available source that depicts the magnitude of chronic disease on the national level and the BRFSS is the best available source for state-specific asthma and diabetes information. The conditions covered in the survey may vary considerably in the accuracy and completeness with which they are reported.

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, 2010. 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, 2010.

U.S. Census Bureau. 2010 Census. Summary File 1, Tables P12, P13, and PCT12.

Office of Management and Budget. Update of Statistical Areas Definitions and Guidance on Their Uses. OMB Bulletin 10-02 December 1, 2009.

U.S. Census Bureau. Small Area Income and Poverty Estimates. State and County Data, 2010.

  1. California, Delaware, Idaho, New York and Virginia.
  2. Maine, New Hampshire, and Ohio.
  3. Alaska for 2007 and Minnesota for 2006.
  4. Arkansas, Colorado, Florida, Massachusetts, North Carolina, South Carolina, South Dakota, and Tennessee.

FACT: Only one city—Santa Fe-Espanola, NM—appeared on all three lists of categories covered in State of the Air for the cleanest air.

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