By SDCN Staff
South Bay, CA–Residents across the South Bay, particularly those near the Tijuana River Valley, experienced elevated hydrogen sulfide (H₂S) emissions over the weekend, producing a strong “rotten egg” odor in affected neighborhoods.
According to the San Diego County Air Pollution Control District, monitors recorded an average H₂S concentration of 384 parts per billion (ppb) between 9 p.m. Sunday and 1 a.m. Monday. The readings exceeded the federal Acute Exposure Guideline Level 1 (AEGL-1) threshold of 360 ppb. The highest levels were detected at the Nestor monitoring station located atop Berry Elementary School, near where Saturn Boulevard crosses the river. Officials say a drop in elevation at that location can create a small waterfall effect, causing wastewater to foam and increasing emissions.
By 10 a.m. Monday, H₂S levels at the Nestor site had fallen to 5 ppb, below the district’s advisory threshold of 30 ppb. Emissions continue to be tracked through the district’s monitoring network, and residents can sign up for alerts when levels exceed advisory thresholds. Real-time data is also available through the County’s Tijuana River Valley dashboard.
County officials said they are continuing to coordinate with regional and federal partners to monitor conditions and provide updates to impacted South Bay communities.
The U.S. Environmental Protection Agency defines AEGL-1 exposure as a level that may cause “notable discomfort, irritation, or certain asymptomatic non-sensory effects,” though impacts are typically temporary and reversible. Officials noted that AEGL-2 levels—associated with more serious health effects—are significantly higher than those recorded during the recent event.
“These ongoing emission exposures to people living in the South Bay are unacceptable,” said Dr. Sayone Thihalolipavan, the County’s public health officer. “While the County of San Diego and others continue to urge federal agencies on both sides of the border to address these flows, there are actions residents can take to reduce exposure.”
Health officials recommend limiting outdoor activity when odors are present, keeping windows and doors closed, and ventilating indoor spaces once conditions improve. Increasing indoor air circulation and using air purifiers equipped with HEPA filters, activated charcoal, and potassium permanganate can help reduce exposure to H₂S.
Residents may also apply for a free air purifier through the Air Pollution Control District. Those purchasing their own units are encouraged to select models verified by the California Air Resources Board.
Individuals with respiratory conditions such as asthma or chronic obstructive pulmonary disease should keep medications readily available and seek medical attention if symptoms worsen or become severe.
