The air toxics respiratory HI indicator is the respiratory HI from the analyzed carcinogens in ambient
outdoor air, as provided by the 2017 Air Toxics Data Update. The data is reported at the Census tract
level. Block group level values are assigned by repeating each parent tract level value.
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.
The lead paint indicator is the percentage of occupied housing units built before 1960, calculated from
the U.S. Census Bureau’s ACS 5-year summary estimates on age of housing stock. EJScreen uses age of
housing stock as a surrogate for potential lead exposure as regulations banning lead-based residential
paint in 1978 led to the reduction and finally an end to the use of such paint in housing. The percentage
of older housing units is a proxy for potential exposure to lead paint and lead-containing dust that
accumulates indoors, in homes, or in other buildings where lead paint was used. EJScreen uses housing
units built before 1960.
The Superfund proximity indicator is reflective of the total count of sites proposed and listed (final) on
the National Priorities List (NPL) 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.
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
The hazardous waste proximity indicator is reflective of the total count of hazardous waste 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. Hazardous waste facilities are defined as
Resource Conservation and Recovery Act (RCRA) handlers that are either operating TSDFs from RCRA or
reporting LQGs from the 2019 BR.
The UST indicator quantifies the relative risk of being affected by a LUST for a block group. The indicator
is derived by the weighted sum of active LUSTs and sum of active and temporarily out of service USTs
within a certain distance from a block group.
The PM 2.5 indicator is a measure of potential exposure to inhalable particles that are 2.5 micrometers or smaller. This is measured in terms of annual average concentration in air measured in micrograms per cubic meter. PM 2.5 information included in EJScreen highlights areas across the U.S. that are not meeting the national ambient air quality standard for PM 2.5. In other words, the levels of PM 2.5 present in these areas are deemed harmful to human health. The PM 2.5 indicator in EJScreen is a measure of potential exposure but not a measure of risk. The raw PM 2.5 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.
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.
The Diesel PM indicator is the estimated concentration of Diesel PM as provided by the 2017 Air Toxics
update. The value of the indicator is in µg /m3
, and reported at the Census tract level. Block group level
values are assigned by repeating each parent tract level value.