Heavily Polluted Tijuana River Drives Regional Air Quality Crisis

Toxic industrial chemicals and untreated sewage have polluted the Tijuana River for decades, recently causing over 1,000 consecutive days of California beach closures. In the summer of 2024, wastewater flows surged to millions of gallons per day despite no rain, enhancing water-to-air hydrogen sulfide (H2S) transfer at a turbulent hotspot. High wastewater flows and low winds led to nighttime H₂S peaks, reaching 4,500 parts-per-billion (ppb)—exceeding typical urban levels of 1 ppb. H₂S levels and community malodor reports were strongly correlated (r = 0.92), validating long-dismissed community voices and highlighting an environmental injustice issue. This study demonstrates that poor water quality can significantly impact air quality—though rarely included in air quality models and health assessments—with widespread implications as polluted waterways increase globally.