Overview

• The Aug. 28 Science paper confirms a water-to-air pathway from the Tijuana River that drives a localized air-quality crisis in San Diego’s South Bay.
• A monitor near Nestor measured hourly hydrogen sulfide around 2,100 parts per billion with nighttime peaks to 4,500 ppb, far above California’s 30 ppb one-hour standard and typical urban levels near 1 ppb.
• Researchers traced emissions to a foamy, churning section near Saturn Boulevard and detected more than 1,000 other gases in the same air mass.
• Gas concentrations fell sharply after a Sept. 10, 2024 wastewater diversion in Mexico, indicating source control can reduce exposures but shifting burdens across the border.
• Residents report headaches and breathing problems, officials have posted warning signs and offered free home air filters, and the EPA says the South Bay wastewater plant expansion was completed this week.