H₂S Air Quality Update or Advisory

The San Diego County Air Pollution Control District (SDAPCD) provides monitoring updates for the communities potentially affected by hydrogen sulfide (H₂S) odors, a gas that can cause a “rotten egg” smell, produced by the transboundary wastewater and sewage flows near the Tijuana River Valley.

SDAPCD has placed community monitoring sites to measure H₂S and has captured the following information:

The California Office of Health Hazard Assessment has established a threshold of 30 parts per Billion of hydrogen sulfide (H₂S) emissions to protect sensitive groups, including children, older adults, and people with certain health conditions. Some individuals may experience odor-related symptoms such as headaches and nausea. H₂S can cause strong odors even at low concentrations.

For current H₂S levels, visit Air Quality Monitoring.

Precautions if odors persist: 

• Limit outdoor activities.
• Create a Cleaner Air Space inside your home by closing windows and doors and use air conditioning if available and/or indoor air purifiers.
  • Households most impacted by odors may qualify for a FREE home air purifier. Visit sdapcd.org/AIRE for more information.
• People with asthma, chronic obstructive pulmonary disease (COPD), or other chronic lung conditions should have their rescue medication(s) readily available. 
• If symptoms from strong odor persists, are worrisome, or worsen, seek medical care.
• If possible, it’s recommended businesses run the HVAC system for 1-2 hours before business hours. 

These precautions are part of the Community Hydrogen Sulfide Guidance, a document developed in partnership with multiple agencies to help interpret hydrogen sulfide (H₂S) threshold levels, about what to expect and recommended actions for each level range. 

 For more information, please visit www.sdapcd.org/TJRiver.

Last Updated: 12/11/25 8:02 AM