Odor Update

The San Diego County Air Pollution Control District (SDAPCD) monitoring equipment located at Nestor – Berry Elementary School has recorded Hydrogen Sulfide (H₂S) levels averaging 166.1 ppB and 131.4 ppB between 8pm-9pm and 9pm-10pm last night (4/19/2025) and 45.0 ppB between 2am-3am early this morning (4/20/2025).

These levels exceeded the 30 parts per Billion threshold¹ established by the California Office of Health Hazard Assessment. This threshold is designed to protect sensitive groups, including children, older adults, and people with certain health conditions. SDAPCD is issuing this notification for communities potentially affected by odors from the Tijuana River Valley. The "rotten egg" smell is caused by H₂S emissions, which can cause strong odors even at low concentrations. Some individuals may experience odor-related symptoms such as headaches and nausea. For current H₂S levels, please visit Air Quality Monitoring.

If odors persist, consider the following precautions to reduce exposure:

• Limit outdoor activities if you smell odor that is bothersome. 
  There are no current active Odor Advisories or Updates at this time.
• Keep doors and windows closed to prevent odor from coming indoors. Air out your home or building when odor is not present (by opening doors and windows, for example).  
  
• For indoor air quality, use air conditioning if available (or a central/portable heating, ventilation, and air conditioning (HVAC) system) and/or indoor air purifiers. Filters (high efficiency particulate air (HEPA) filter, for example) with activated charcoal (plus potassium permanganate, if available) are recommended.  Certain households may qualify for a free home air purifier. Go to sdapcd.org/AIRE for more information about the AIRE air purifier program.
  
• If possible, businesses should run the HVAC system for 1-2 hours before business hours. 
  
• 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.

^[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). This small unit is particularly useful in environmental monitoring because it allows for precise measurement of trace gases, like hydrogen sulfide (H₂S), even at very low concentrations.

For example, a measurement of 30 ppb of H₂S in the air means there are 30 molecules of hydrogen sulfide for every billion molecules of air. Since some gases can impact health at very low levels, ppB provides a helpful scale to gauge safety and detect pollutants at levels relevant to public health.

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

Last Updated: April 20, 2025, at 7:30 a.m.