Methodology and Acknowledgements

The Air Quality Data

Description of County Grading System

Calculations of Populations-at-Risk

The Air Quality Data


Statistical Methodology: 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 three-year period for 2012-2014 for each monitoring site.

Design values for the annual PM2.5 concentrations by county for the period 2012-2014 came from data posted on August 19, 2015, at EPA's website at On December 18, 2014, and on March 31, 2015, EPA made additional updates to the information at

Ozone Data Analysis

The 2012, 2013, and 2014 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 September 11, 2015. The data were considered for a three-year period for the same reason that the 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 2012, 2013, and 2014, based on the EPA-defined ozone season, was identified.

The current national ambient air quality standard for ozone is 70 parts per billion (ppb) measured over eight hours. The EPA's Air Quality Index reflects the 70 ppb 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 the EPA based on the EPA Air Quality Index:

0 – 54 ppb Good (Green)
55 – 70 ppb Moderate (Yellow)
71 – 85 ppb Unhealthy for Sensitive Groups (Orange)
86 – 105 ppb Unhealthy (Red)
106 – 200 ppb Very Unhealthy (Purple)
>201 ppb 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. Unlike the form of the previous 0.075 ppm 8-hour average ozone standard that was established in 2008, the daily maximum 8-hour average concentration for a given day is derived from the highest of the 17 consecutive 8-hour averages beginning with the 8-hour period from 7:00 a.m. to 3:00 p.m. and ending with the 8-hour period from 11:00 p.m. to 7:00 a.m. the following day (i.e., the continuous 8-h averages running from 7:00 a.m. to 11:00 p.m.). 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 13 of the possible 17 8-hour averages). Because the EPA includes days with inadequate data if the standard value is exceeded, our data capture methodology included the site's 8-hour value if at least one valid 8-hr period were available and it was 71 ppb or higher.

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 2012, 2013, and 2014 with monitoring information. The 24-hour PM2.5 data were downloaded on August 20, 2015. 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 three years, the number of days the maximum of the daily PM2.5 concentration was within the ranges identified by the EPA based on the EPA Air Quality Index, as adopted by the EPA on December 14, 2012:

0.0 µg/m3 to 12.0 µg/m3 Good (Green)
12.1 µg/m3 to 35.4 µg/m3 Moderate (Yellow)
35.5 µg/m3 to 55.4 µg/m3 Unhealthy for Sensitive Groups (Orange)
55.5 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)

All previous data collected for 24-hour average PM2.5 were characterized using the AQI thresholds listed above.

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:

  1. 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.
  2. Next, multiplied the total number of days within each category by their assigned factor, and then summed all the categories to calculate a total.
  3. 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  
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

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 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 and the 24-hour PM2.5 standards. The EPA determines whether a county violates the standard based on the fourth 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 2015 ozone standard. The American Lung Association's position is that the evidence shows that the 2015 ozone standard, although stronger than the 2008 standard, still fails to adequately 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 2013 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 the 2012 National Ambient Air Quality Standard for annual PM2.5 of 12 µg/m3. Counties that EPA listed as being at or below 12 µg/m3 were given grades of "Pass." Counties EPA listed as being at or above 12.1 µg/m3were given grades of "Fail." Where insufficient data existed for EPA to determine a design value, those counties received a grade of "Incomplete."

EPA officially recognized that data collected in all Illinois and Florida counties and most Tennessee counties were processed in certain laboratories where quality control issues meant that available data could not be considered for development of an official design value. For short-term and annual particle pollution, 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 2013 as defined by the OMB.

The Lung Association received critical assistance from members of the National Association of Clean Air 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. & Associates. Questions about the annual PM design values were discussed with EPA; however, the Lung Association made final decisions to grade counties as "Incomplete" where EPA considered PM 2.5 data to have inadequate quality assurance. 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 exception to this is poverty, for which estimates are available at the county level.

Population Estimates

The U.S. Census Bureau estimated data on the total population of each county in the United States for 2014. The Census Bureau also estimated the age-specific breakdown of the population and how many individuals were living in poverty by county. These estimates are the best information on population demographics available between decennial censuses.

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 Obstructive Pulmonary Disease, Cardiovascular Disease, Asthma and Diabetes. In 2014, the Behavioral Risk Factor Surveillance System (BRFSS) survey found that approximately 21.6 million (8.4 percent) of adults residing in the United States and 9.2 percent of children from thirty-seven states and Washington, D.C., reported currently having asthma. Among adults in the Unites States in 2014, 16.1 million (6.6 percent) had ever been diagnosed with chronic obstructive pulmonary disease (COPD), 20.9 million (7.8 percent) had ever been diagnosed with cardiovascular disease, and 25.4 million (8.4 percent) had ever been diagnosed with diabetes.

The prevalence estimate for pediatric asthma is calculated for those younger than 18 years. Local area prevalence of pediatric asthma is estimated by applying 2014 state prevalence rates, or if not 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 2014 BRFSS were available for thirty-seven states and Washington D.C., from the 2013 BRFSS for one state, from the 2012 BRFSS for two states, from the 2011 BRFSS for one state, and national data were used for the ten states 1 that had no data available. Data from earlier years were not used due to changes in the 2011 survey methodology.

The prevalence estimate for COPD, cardiovascular disease, adult asthma and diabetes is calculated for those aged 18-44 years, 45-64 years and 65 years and older. Local area prevalence for these diseases is estimated by applying age-specific state prevalence rates from the 2014 BRFSS to age-specific county-level resident populations obtained from the U.S. Census Bureau web site. Cardiovascular disease included ever having been diagnosed with a heart attack, angina or coronary heart disease, or stroke.

Limitations of Estimates. Since the statistics presented by the 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 the BRFSS 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 BRFSS is the best available source for information on the magnitude of chronic disease at the state level. 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 or state estimates derived from the BRFSS.


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

Centers for Disease Control and Prevention. Behavioral Risk Factor Surveillance System, 2014.

Population Estimates Branch, U.S. Census Bureau. Annual Estimates of the Resident Population by Selected Age Groups and Sex for Counties: April 1, 2010 to July 1, 2014.

Office of Management and Budget. Revised Delineations of Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Combined Statistical Areas, and Guidance on Uses of the Delineations of These Areas. OMB Bulletin 13-01 February 28, 2013.

U.S. Census Bureau. Small Area Income and Poverty Estimates. State and County Data, 2014.


The American Lung Association "State of the Air® 2016" is the result of the hard work of many people:

In the American Lung Association National Office: Paul G. Billings, who supervised the work; Janice E. Nolen, MA, who directed the project, analyzed data, wrote the text, and coordinated print and web presentations; Thu Anh Vu Tran, who assisted with the data analysis and report preparation; Lyndsay Moseley Alexander and Laura Kate Bender, who integrated the Healthy Air Campaign with this report; Zach Jump, MA, who converted the raw data into meaningful tables and comparisons and calculated all the population data; Susan Rappaport, MPH, who supervised the data analysis; Norman Edelman, MD, and Al Rizzo, MD, who reviewed the science and health discussions; Neil Ballentine, who directed the online presentation; Todd Nimirowski, who designed and created the user experiences online; Lauren Innocenzi and MacKenzie Olsberg, who managed content production online; Laura Lavelle, who developed social sharing and digital engagement strategy; Kim Lacina, Allison MacMunn, and Gregg Tubbs, who coordinated internal and external communications and media outreach; Michael Albiero, who designed the logo and report cover; and Craig Finstad, who coordinated sharing the data with direct mail donors.

In the nationwide American Lung Association: All Lung Association charters reviewed and commented on the data for their states. Hard-working staff across the nation went out of their way to ensure that their state and local air directors were informed and had a chance to review the draft data.

Outside the American Lung Association: Allen S. Lefohn of A.S.L. and Associates, who compiled the data; Deborah Shprentz, who assisted with the research and review of the science; Beaconfire RedEngine Consulting, who uploaded the data to the website; and Our Designs, Inc., who designed the print version.

Great appreciation goes to the National Association of Clean Air Agencies, who along with their Executive Director Bill Becker, strove to make this report better through their comments, review and concerns. Many of their members reviewed and commented on the individual state data presented and the methodology to make this report more accurate. We appreciate them as our partners in the fight against air pollution. This report should in no way be construed as a comment on the work they do.

The American Lung Association assumes sole responsibility for the content of the American Lung Association "State of the Air® 2016".

1. 2013: Arizona. 2012: North Dakota and Wyoming. 2011: Iowa. National: Alaska, Arkansas, Colorado, Delaware, Florida, Idaho, Minnesota, South Carolina, South Dakota, and Virginia.

Did You Know?

Did You Know?Ozone and particle pollution are both linked to increased risk of lower birth weight in newborns.

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