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.


The 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 individual pollutant measures that could be loaded into the interactive charts on this page. Median annual values were extracted directly from the AQI data files for each county. Unlike for AQI, the Concentration by Monitor files do not contain county-mean values, but instead pollutant measures from individual monitors available in each county. An NCL script was written to parse this information and calculate the mean of all monitors within a county for selected pollutants. These 10 slected pollutants follow, shown as labeled in the datafiles with the 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. For each of these, the mean was calculated for the highest annual values recorded at each monitor.