The Shelby County Health Department has raised questions about the integrity of data behind a May community air monitoring project report that indicated that South Memphis residents are being regularly exposed to unhealthy air pollution.
In a statement to the Lookout, the health department wrote that the monitors used by the project are not approved by the Environmental Protection Agency for regulatory purposes, and can have a high sampling error depending on weather conditions.
The researchers behind the report countered that they followed guidelines and corrective equations published by the EPA to calibrate data from the PurpleAir monitors they used to measure fine particle pollution.
The Center for Engagement, Environmental Justice, and Health INpowering Communities, CEEJH INC, partnered with Memphis Community Against Air Pollution to place PurpleAir monitors in South Memphis, collecting data from Nov. 11 through March 11.
The organizations behind the report took air quality testing into their own hands because of the lack of a government air monitoring site in South Memphis for more than a decade. The Shelby County Health Department plans to reopen a South Memphis monitoring site this month.
The lower-cost PurpleAir monitors measure a mixture of tiny solid and liquid particles in the air that can come from sources like construction or fires or form through reactions between chemicals released by power plants, industrial operations and vehicles. Inhaling these fine particles has been repeatedly linked to heart and lung issues, particularly in people who are more sensitive to exposure due to heart or lung disease, according to the Environmental Protection Agency.
While EPA’s air quality map and trends tracker show particulate levels in the “good” and “moderate” range in Memphis over the last several months, the PurpleAir monitors found the average concentration of fine particulate matter at three South Memphis test sites exceeded the EPA’s annual standard during all times of day, according to the CEEJH INC report.
“The SCHD Air Monitoring Program is dedicated to accuracy and precision in data collection and transparency in reporting. The data they collect is available to everyone on the AirNow.gov webpage but is not official until validation and certification are complete,” the health department stated.
Health Department says pollution levels are within EPA standards
The Memphis metropolitan area has five official air monitors: three in Shelby County, one in Arkansas and one in Mississippi.
In 2026, none of the monitors within Shelby County’s Ambient Air Monitoring Network or networks in the Memphis metro area have recorded levels exceeding EPA standards, the health department stated.
“That is precisely why we are conducting more hyperlocal monitoring,” CEEJH INC Director of Research and Policy Vivek Ravichandran wrote in a statement to the Lookout. Currently, the closest Shelby County Health Department monitoring station is 15 to 20 miles away from some South Memphis neighborhoods. Other monitoring studies have shown that air pollution can differ substantially block by block, even for blocks less than one mile apart, Ravichandran wrote. EPA regulatory monitors are designed to assess broad exposure, but might not capture localized “hot spots” that could be associated with industrial facilities, the xAI supercomputer, or other sources in South Memphis.
“The absence of exceedances at distant SCHD or metropolitan monitors should not be interpreted as evidence that Boxtown/South Memphis residents are not experiencing elevated or cumulative exposures,” he wrote. “Rather, it supports the need for community-scale monitoring to reduce exposure misclassification and better characterize the actual pollution burden experienced by residents.”
For particulate matter less than 2.5 micrometers in diameter — about one-thirty-sixth the size of a grain of sand — federal standards set limits at 35 micrograms per cubic meter of air for daily exposure. The annual exposure standard is 9 micrograms per cubic meter, and compliance is determined through a calculation using three years of EPA-approved data.
“Long-term exposure is a weighted average that is calculated over an entire year,” the health department stated. “It must not be compared to a short-term period.”
The CEEJH INC report found that average concentrations at monitoring locations in Boxtown, Westwood/Whitehaven and Southaven exceeded 9 micrograms per cubic meter in 62 percent of all monitored hours. The Westwood/Whitehaven location topped the annual standard in 75 percent of monitored hours.
“While our four-month monitoring period cannot substitute for a three-year regulatory compliance determination, it provided valuable evidence regarding chronic exposure conditions,” Ravichandran wrote.
Unhealthy for whom?
The EPA uses the Air Quality Index to report daily air quality based on the levels of five common pollutants, including fine particulate matter. The index scale runs from green (good) to maroon (hazardous).
The Shelby County Health Department noted that the EPA does not consider code yellow or “moderate” air quality days “unhealthy” for most people.
A code orange day is considered “unhealthy for sensitive groups,” according to the EPA. This includes people with “pulmonary and cardiac conditions, along with the elderly, very young, and individuals involved in strenuous activity for extended periods,” the health department stated.
Ravichandran and his team stated that recent research shows that long-term exposure to lower fine particulate concentrations, even below the code yellow standard, can have health consequences. They cite a study of a nationwide Medicare cohort of more than 60 million adults aged 65 and older that found that long-term exposure, even at low levels, was associated with increased mortality risk.
“Our Memphis monitoring study was designed to evaluate chronic community exposure, not daily (Air Quality Index) classifications,” Ravichandran wrote.
The report’s findings that concentrations exceeded 9 micrograms per cubic meter for most of the monitored period “indicates that residents may be experiencing sustained elevated background pollution over extended periods, even when daily (Air Quality Index) values may remain in the moderate category.”
Relying solely on Air Quality Index categories “may underestimate the potential long-term health implications for communities experiencing persistent, cumulative exposures, particularly for populations already burdened by existing environmental and health disparities,” Ravichandran wrote.
Questioning calibrations
The Shelby County Health Department also pointed out that on days that the PurpleAir monitors recorded higher daily average concentrations of fine particulate matter, temperatures were cold and humidity was high. In these conditions, the PurpleAir monitors may have a “high bias,” the department stated.
Researchers initially placed the PurpleAir monitors next to EPA-approved Shelby County monitors to calibrate them in accordance with EPA guidelines. But the health department stated that “they would need to be routinely collocated and compared” to the Shelby County monitors to support data integrity. The Shelby County monitors are verified monthly.
Ravichandran wrote that his team selected PurpleAir monitors in part because the EPA has published a correction formula to calibrate data and adjust for biases.
The research project’s methods are similar to previously approved quality assurance plans, he added.
“Comparing to annual standards even given the short duration of our study is important because we still get a glimpse of chronic long-term exposure to residents,” Ravichandran wrote.
CEEJH INC and Memphis Community Against Pollution plan to expand air monitor placement to sites in Mississippi and Arkansas and issue another follow-up report in several months.
