H₂S Air Quality 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:

Locations	Date	Time	H2S Levels (ppB[1])
Berry Elementary School	4/17/26	10 PM - 11 PM 11 PM - 12 AM	40 187
Imperial Beach Civic Center	4/17/26	11 PM - 12 AM	36
Berry Elementary School	4/18/26	12 AM-1 AM	255
Imperial Beach Civic Center	4/18/26	1 AM-2 AM	43
[1] "parts per billion" or ppB is a unit of measurement used to describe the concentration of a substance in the air, water, or soil. Specifically, one part per billion means one part of a substance per one billion parts of the medium (such as air).

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: April 18, 2026 at 05:40 AM