SAN DIEGO (CNS) — In a little less than a year, an air purifier program to protect the health of South Bay residents has distributed more than 10,000 devices to mitigate the effects of hydrogen sulfide odors.
The San Diego County Air Pollution Control District began the Air Improvement Relief Effort Program in February 2025 and this week reached the 10,000 milestone for homes in San Diego and Imperial Beach.
The program provides a free air purifier and up to two replacement filters containing activated carbon and potassium permanganate -- intended to reduce compounds such as hydrogen sulfide from the indoor air.
"This milestone represents a significant accomplishment in our efforts to help South Bay residents whose quality of life has been impacted by hydrogen sulfide in the ambient air," said Paula Forbis, SDAPCD air pollution control officer. "It was a major undertaking for an agency of our size, but SDAPCD wants the community to know that we are doing everything we can to help improve air quality conditions for South Bay communities."
The district conducted a survey last summer of households that had received the purifiers, and most said they had helped with odors.
SDAPCD leaders said Monday they will allocate an additional $1 million to continue providing the purifiers to eligible households. The additional funding will cover around 3,500 new purifiers.
The odors of hydrogen sulfide and other toxic gases are not new to the southern part of the county near the Tijuana River.
In research published last year, scientists from UC San Diego's
Scripps Institution of Oceanography, UC Riverside, San Diego State University and the National Science Foundation's National Center for Atmospheric Research found that extremely high levels of the toxic gas hydrogen sulfide -- among others -- are making their way into the homes and lungs of many in the county.
"This study reveals a direct airborne pollutant exposure pathway -- from contaminated rivers into the air we breathe," said Kimberly Prather, the lead investigator of the study, a UCSD professor and director of the Center for Aerosol Impacts on Chemistry of the Environment. "For the first time, we've shown that poor water quality can profoundly degrade air quality, exposing entire communities to toxic gases and other pollutants. These findings validate the experiences of residents who have endured this crisis for decades, and also underscore the urgent need for action to protect public health in San Diego and in vulnerable communities worldwide."
In 2024, the number of foul odor complaints spiked precipitously among residents near the Tijuana River. Enough so that Prather told her team to pull out of the area until the gas levels dropped. The readings the team took found levels of hydrogen sulfide -- also known as sewer gas because of the rotten egg, sewage smell it emits -- 4,500 times more than what is typical for an urban area.
Strangely, though, the highest readings were not coming from the river itself or even the ocean, but in an inland area in the Nestor neighborhood.
What the scientists found was that a wastewater discharge pipe was expelling thousands of gallons of sewage into a confined area, creating turbulence and foam. When the bubbles in the foam burst, they released gases into the air -- more than 1,000 different kinds, including many that are toxic.
These aerosolized pollutants then produced the noxious odors residents had
noted for years.
"The community was acting as sensors, but felt they were being dismissed," Prather said.
Once the source of much of the smell was located, the UCSD team began monitoring gas levels at the site off Saturn Boulevard, which became known as the "hot spot."
Elevated gas levels corresponded to increase odor complaints at an almost perfect correlation.
The residents of the area had clocked the noxious gas better than scientific measurements up to that point.
Symptoms reported to that point mirrored those associated with exposure to hydrogen sulfide.
According to UCSD, the health effects of long-term exposure to hydrogen sulfide are not fully understood, but the California Office of Environmental Health Hazard Assessment sets a chronic exposure limit of 7.3 parts per billion, while the California Air Resources Board's one-hour standard is 30 ppb, a level based on odor, not health.
The teams monitoring the South Bay found peaks as high as 4,500 ppb and up to an average of 2,100 ppb for one hour -- peaking at night, when winds die down.
"This level is too high for chronic exposures as 30 parts per billion
is already associated with headaches, nausea, respiratory symptoms and
other adverse health effects, particularly among vulnerable populations," said
Paula Stigler Granados, an environmental health scientist at SDSU's School of
Public Health. "Framing this as merely an odor issue dangerously understates
the real public health risks of repeated exposure to toxic gases at such
concentrations."
The San Diego Air Pollution Control District has an online air quality dashboard showing current levels of hydrogen sulfide to help residents limit their exposure when concentrations are high. The SDAPCD also sends alerts to all residents when hydrogen sulfide levels exceed 30 ppb.
For more information about the AIRE program, including requirements
and application, visit sdapcd.org/filter.
Copyright 2026, City News Service, Inc.
