Ozone Data and Maps
We created the ozone map with publicly available data from the U.S. Environmental Protection Agency's (EPA) AirData Website.1 We downloaded annual summary data for ground-level ozone concentrations from 2011 through 2015. The data sets included a field calculated by the EPA representing the number of days per year when an eight-hour average concentration of ozone exceeded the 2015 Ozone National Ambient Air Quality Standards (0.070 parts per million).2 For each U.S. county, we averaged data from the 2011–2015 period to determine the average number of ozone exceedance days annually at the county level. Multiple monitors at a single site were averaged, and only monitors with at least 75 percent data completeness in each of the five years were included. Counties with a single monitor were assigned that monitor’s average number of ozone exceedance days per year. For counties with multiple monitors, the county was assigned a mean of the monitor-level means.
Ragweed Data and Maps
We used the Early Detection and Distribution Mapping System (EDDMapS)3 from the Center for Invasive Species and Ecosystem Health at the University of Georgia to assess whether U.S. counties had confirmed reports of the presence of common ragweed (Ambrosia artemisifolia)
Counties with Both Ozone Exceedance Days and Ragweed
NRDC's analysis subsequently created a map showing those counties in the 50 states having both: (1) an average of one or more unhealthy ground-level ozone days per year from 2011-2015; and (2) the reported presence of common ragweed (Ambrosia artemisiifolia) as of 2016. Estimates of populations potentially affected by these conditions were taken from the 2015 Census.4
On state pages, we ranked the states based on the percentage of residents living in counties reported to have both an average of one or more unhealthy ground-level ozone days per year and the reported presence of ragweed, with population estimates taken from the 2015 Census. For states with only ozone or ragweed, we showed the corresponding percentage of residents living in affected counties and did not do a ranking.
"Asthma Capital" Cities
The Asthma Capitals report5 is a yearly research project of the Asthma and Allergy Foundation of America (AAFA),6 a nonprofit organization dedicated to helping patients with asthma and allergies. AAFA ranks the 100 largest U.S. metro areas by looking at multiple factors, including how common asthma is, environmental conditions (including annual pollen measurements and length of peak pollen season), and health care use. Cities are ranked from highest total score to lowest total score, with rank #1 indicating the most challenging city to live in with asthma.
We overlaid the top 50 Asthma Capitals from 20157 on the NRDC map layer showing both an average of one or more unhealthy ground-level ozone days per year and the reported presence of ragweed. NRDC's analysis shows that of these top 50 Asthma Capitals, 34 occurred in counties with both unhealthy ground-level ozone smog levels and reported ragweed presence.
1. U.S. Environmental Protection Agency, “Pre-Generated Data Files: Annual Summary Data,” http://aqsdr1.epa.gov/aqsweb/aqstmp/airdata/download_files.html#Annual (accessed May 1, 2017).
2. U.S. Environmental Protection Agency, “2015 Ozone National Ambient Air Quality Standards (NAAQS) Nonattainment Actions,” https://www.epa.gov/ozone-pollution/2015-national-ambient-air-quality-standards-naaqs-ozone (accessed May 1, 2017).
3. Early Detection & Distribution Mapping System (EDD MapS), “Common Ragweed, Ambrosia artemisiifolia L.,” https://www.eddmaps.org/distribution/uscounty.cfm?sub=5076&map=distribution, 2017 (accessed May 1, 2017).
4. U.S. Census Bureau, “2011-2015 American Community Survey 5-Year Estimates,” https://factfinder.census.gov, 2015, (accessed June 5, 2017).
5. Asthma and Allergy Foundation of America, “2015 Asthma Capitals,” http://www.aafa.org/page/asthma-capitals.aspx, 2015 (accessed May 1, 2017).
6. Asthma and Allergy Foundation of America, “About AAFA,” www.aafa.org/page/about-aafa.aspx (accessed May 1, 2017).
7. Asthma and Allergy Foundation of America, “2015 Asthma Capitals.”
Project teams: NRDC Science Center, Communications Department, Climate & Clean Air program
Researchers and writers (alphabetical order): Tom Barkley, Juanita Constible, Kim Knowlton, Alex Krefetz, Jillian Mackenzie, Lauren Reiser, Christina Swanson
Reviewers (alphabetical order): Sean Alcorn, Juan Declet-Barreto, Ariana Gonzalez, Aliya Haq, Karen Hobbs, Alex Jackson, Patrick Kinney, Noah Long, Nick Magrisso, Katharine McCormick, Jackson Morris, Miriam Rotkin-Ellman, Christina Swanson, John Walke, Samantha Williams
Editor: Sarah Engler
Data analysis and map production (alphabetical order): Alex Hart, Kate McKenney, ZevRoss Spatial Analysis