Air Quality Mapper

This page displays county-level U.S. EPA annual Air Quality Index (AQI) values and 10 pollution measures for the period 1980 – present. The color-coded values of a selected measure are shown for each county on the map. Move the slider (above the map) to see the values change over time. Refer to the color legend below the map; gray indicates no available data. Select a specific air quality measure by clicking one of the labeled buttons (AQI, Ozone, PM2.5, etc.). These buttons are color-coded and display the current measurement for a selected county. Select a specific county by either clicking on the map or by searching a ZIP code (input box at top-right of map). The final page element is a bar chart, positioned below the map, that displays the annual time series for the currently selected county and air quality measure. Clicking on the bar chart will update the map for the selected year.

Descriptions for each of the air quality measures are on the Pollutants & Standards page.

Data Source: EPA Air Data Annual Summaries

Methods

EPA’s annual summary datafiles for Air Quality Index (AQI) by County and Concentration by Monitor were downloaded and processed using NCAR Command Language (NCL) to generate files for AQI and 10 individual pollutant measures that could be loaded into the interactive charts on this page. These pollutants are shown below with the corresponding concentration measurement interval:

Ozone (8-hour), PM25 (Annual), PM10 (24-hour), SO2 (1-hour), NO2 (1-hour), CO (1-hour), Nickel (24-hour), Lead* (24-hour), Cadmium (24-hour), Arsenic (24-hour).
*Measurements utilized from both "Lead (TSP)" and "Lead PM2.5 LC" monitors to fully capture available data.

The annual AQI datafiles contain pre-calculated county-level median annual values. The "Concentration by Monitor" files, in contrast, do not contain county-level values, and so these were instead calculated from all available measurements within each county for each pollutant using NCL. These means were furthermore calculated from the data column "1st Max Value" (The highest value for the year).