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In February, the U.S. EPA set a more stringent standard for airborne particulate matter small enough to infiltrate human lungs, lowering it from 12 to 9 micrograms per cubic meter (per 35 cubic feet). Areas with air quality consistently worse than the standard earn a “nonattainment” label and are meant to get special consideration in emissions reduction policy decisions.
“To accompany the new standard, new monitors are needed.”
But the current EPA air monitoring network cannot detect all nonattainment areas in the United States under this new standard and misses air pollution hot spots, according to a study published in Environmental Science and Technology Letters. Adding just 10 additional sensors could greatly improve the network’s coverage, the study’s authors claim.
“To accompany the new standard, new monitors are needed; otherwise, the standard will not be effective,” said Yuzhou Wang, an environmental engineer at the University of California, Berkeley, and lead author of the new study.
Data Gaps
PM2.5 describes particles with diameters of 2.5 micrometers or smaller. These particles are inhalable and key indicators of both indoor and outdoor air quality. EPA makes regulatory decisions regarding PM2.5 pollution based on monitoring from its State and Local Air Monitoring Stations (SLAMS) network. Individual monitors are maintained by state and local agencies.
To determine how well the SLAMS network captures PM2.5 in the United States, Wang and her colleagues compared data from the network from 2017 to 2019 to census tract–level, spatially complete PM2.5 air pollution estimates from a model created by the Center for Air, Climate, and Energy Solutions for the same time period. The model estimates PM2.5 concentrations within each census tract on the basis of monitoring and satellite data and information about an area’s land use.
They found that under the new standard, the current EPA monitoring network fails to identify 44% of nonattainment areas—affecting about 20 million people. These nonattainment areas may have SLAMS monitors in locations that meet the PM2.5 standard, but some census tracts within these areas still had PM2.5 concentrations exceeding the standard that were not captured by the SLAMS network because monitors are not necessarily placed in the most polluted locations.
Researchers also found that 2.8 million people live in uncaptured census tracts with PM2.5 above the standard, which they termed “pollution hot spots.”
“We knew these monitors may not be enough,” Wang said. “But we didn’t think the gap would be so large.”
“The monitoring network that we have now reflects the previous standard,” said Sherri Hunt, an atmospheric chemist at EPA’s Air, Climate, and Energy Research Program who wasn’t involved with the new study. “When we decrease the standard, we expect that there will be some changes in terms of the monitoring network.”
All census tracts that the researchers identified as PM2.5 “hot spots” (both those captured by the EPA network and those not) had higher percentages of people of color and low-income residents than the overall population.
“We have to use different methods in order to identify the sources that are causing [disparities in exposures].”
“Because the monitors are not evenly distributed, communities [that include] people of color, low-income populations, and historically discounted communities will receive less protection,” Wang said. Communities with high levels of PM2.5 missed by the current monitoring network may be passed up for opportunities or funding meant to improve air quality, she said.
The SLAMS network was designed to measure overall air pollution across the whole country rather than to identify or decrease exposure disparities, Hunt said. “We have to use different methods in order to identify the sources that are causing [disparities in exposures].”
Growing the Network
Adding just 10 additional monitors, mainly in the South and Midwest, would reduce the population remaining in uncaptured PM2.5 hot spots by 67%, according to Wang and her coauthors.
Wang recommended that EPA use additional tools, such as lower-cost or mobile air monitoring stations, as part of its network to achieve higher spatial resolution. Getting that finer-scale view would also help to address the inequitable coverage of the current air monitoring network, she said.
Hunt said it’s unlikely that EPA would integrate low-cost sensors or mobile monitors into the SLAMS network because data collected by the network must meet stringent federal standards. “We really want to make sure measurements from the SLAMS instruments are as accurate as they can be and that we understand the quality of the data,” she said.
EPA revised its monitoring requirements along with the new standard and plans to make changes to the monitoring network to better protect overburdened communities. The agency has identified a handful of expected new sites, though the actual number and locations of the sites will likely be updated, said Shayla Powell, a public affairs specialist at EPA. Any additional or moved sites must be operational by 2027.
—Grace van Deelen (@GVD__), Staff Writer
Citation: van Deelen, G. (2024), EPA air monitoring network misses 2.8 million Americans in pollution hot spots, Eos, 105, https://doi.org/10.1029/2024EO240489. Published on 1 November 2024.
Text © 2024. AGU. CC BY-NC-ND 3.0
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