The ozone indicator in EJScreen reflects potential ozone exposure measured in terms of summer
seasonal daily average maximum concentrations in an 8-hour period measured in parts per billion.
Ozone information included in EJScreen highlights areas across the U.S. that are not meeting the
national ambient air quality standard for ozone. In other words, the levels of ozone present in these
areas are deemed harmful to human health.
The ozone indicator in EJScreen is a measure of potential exposure but not a measure of risk. The raw
ozone data is compiled by census tract, which is supplied for use in the tool by EPA’s OAQPS. For air
toxics risk measures (as opposed to exposure) users can turn to EJScreen’s other three indicators: cancer
risk, respiratory HI, and diesel PM.
EJ Screen Traffic Proximity
The traffic proximity indicator is based on AADT count divided by distance in meters from the Census
block centroid. The proximity score is based on the traffic within a search radius of 500 meters (or
further if none is found in that radius). This distance was selected to be large enough to capture the
great majority of road segments (with traffic data) that could have a significant impact on the local
residents, balanced against the need to limit the scope due to computational constraints. The closest
traffic is given more weight, and the distant traffic is given less weight, through inverse distance
weighting. For example, traffic 500 meters away is given only one tenth as much weight as traffic 50
meters away.
EJ Screen RMP Facility Proximity
The RMP facility proximity is reflective of the total count of RMP facilities in each block group within 5
km of the average resident in a block group, divided by distance, calculated as the population-weighted
average of blocks in each block group
Threatened and Endangered Species by County
This layer displays the number of threatened and endangered species in each county. Additional layers are available for the type of species, such as plants, animals, invertebrates, and more!
Weeks In Drought
This layer displays the percentage of weeks in any severity of drought for the years 2021-2023.
Drought Intensity, U.S. Drought Monitor
This layer displays areas that experienced dry or drought conditions in the last seven days. Data are retrieved as shapefiles from the U.S. Drought Monitor and are updated on a weekly basis. The affected areas are represented by polygons, which are classified according to drought intensity. Using quantitative and objective indicators, as well as local condition and impact reports, the U.S. Drought Monitor defines each drought intensity level as follows:
D0 – Abnormally Dry
D1 – Moderate Drought
D2 – Severe Drought
D3 – Extreme Drought
D4 – Exceptional Drought.
For more information about the data, please see the U.S. Drought Monitor Data Classification web page.
Real-time Air Quality Index (AQI) – Ozone and Particulate Matter
This US EPA feature layer is updated hourly and reflects the latest hour of air quality data received from each monitoring site that reports to AirNow. The concentration and AQI values are for Ozone and Particulate Matter (PM) only. Air quality index ranges from 0-5,000 with higher values indicating worse air quality.
Real-time Air Quality Index (AQI) – Ozone and Particulate Matter
This US EPA feature layer is updated hourly and reflects the latest hour of air quality data received from each monitoring site that reports to AirNow. The concentration and AQI values are for Ozone and Particulate Matter (PM) only. Air quality index ranges from 0-5,000 with higher values indicating worse air quality.
Weeks In Drought
This layer displays the percentage of weeks in any severity of drought for the years 2021-2023.
Threatened and Endangered Species by County
This layer displays the number of threatened and endangered species in each county. Additional layers are available for the type of species, such as plants, animals, invertebrates, and more!