Hydrogen Sulfide Monitoring
Environmental Factors and Data Collection
Several factors can influence hydrogen sulfide (H2S) concentration
readings, including weather conditions, proximity to sewage flow, and
other environmental variables. These factors are important to consider
when interpreting the data collected by monitoring instruments.
The data above was gathered using Teledyne T101 instruments at three
locations: San Diego Fire Station #29 in San Ysidro, Berry Elementary
School in the Nestor community, and the City of Imperial Beach Civic
Center. These instruments provide real-time, minute-by-minute
measurements of H2S concentrations to produce the hourly averages
reported in the dashboard. The data is reported in hourly averages to
be able to compare it to existing state and federal standards for H2S exposure.
Data Reporting and Interpretation
To facilitate comparison with established standards for H2S
exposure, the monitoring instruments generate hourly averages
from the minute-by-minute readings. It is important to note that H2S
is a highly unstable gas that reacts rapidly in the atmosphere,
leading to significant fluctuations in minute-by-minute
concentrations. Therefore, the hourly average reported does not
represent the same concentration throughout the hour, but rather
incorporates all values measured within that time frame.
H2S
concentrations can vary across different areas of the community. The
monitoring network is designed to provide a representative sample of
the general community’s H2S levels. This information enables the
public to stay informed about local H2S concentrations and to take
recommended actions to reduce exposure, as outlined in the Community
Hydrogen Sulfide Guidance. Since sensitivity to H2S differs from
person to person, it is advised that individuals follow the guidance
to minimize exposure, regardless of the concentrations reported by the
monitoring network.
Collaboration and Data Sharing
The San Diego Air Pollution Control District (SDAPCD) collaborates and shares data with governmental agencies such as the County of San Diego Department of Public Health Services and institutions conducting research in the area. Some of these institutions include the Centers for Disease Control and Prevention (CDC) Agency for Toxic Substances and Disease Registry (ATSDR) which is currently conducting an evaluation of potential health risks in the Tijuana River Valley. Also, we have shared data with the University of California San Diego, which is leading a field study on cross-border water sewage pollution and its impacts on air quality.
Community Hydrogen Sulfide Guidance
In partnership with the County of San Diego, and in consultation with the California Department of Public Health (CDPH), U.S. Agency for Toxic Substances and Disease Registry (ATSDR), and the U.S. Environmental Protection Agency (EPA), a Community Hydrogen Sulfide Guidance document was developed to help interpret hydrogen sulfide (H2S) threshold levels.
The Community Hydrogen Sulfide Guidance gives guidance for South Bay residents and visitors about the San Diego County Air Pollution Control District's (SDAPCD’s) measurements, in parts per billion (ppB), of hydrogen sulfide (H2S) from the Tijuana River at community sites. See below to learn about what to expect and recommended actions for each level range.
A copy of the Community Hydrogen Sulfide Guidance is available here. Español.
Measurement at Community Monitor (1-Hour Avg.) | What to Expect | Recommendations |
Green
| Most people will not smell an odor or experience odor-related symptoms. SDAPCD will continue to monitor H2S levels and post them on the Tijuana River Valley website. |
|
Yellow
| Some sensitive groups may smell an odor and experience odor-related symptoms such as headaches, nausea, or respiratory discomfort. SDAPCD will continue to monitor H2S levels and post them on the Tijuana River Valley website. |
|
Orange
| Many people will smell an odor and/or experience odor-related symptoms. SDAPCD will continue to monitor H2S levels and post them on the Tijuana River Valley website. SDAPCD will also release an 'Odor Advisory' on the Tijuana River Valley website. Odor Advisory messaging will be shared through social media.1 SDAPCD email subscription service, and through partner agencies and organizations, including schools and community-based organizations. For levels 200 ppB or higher, SDAPCD will activate multiagency review to develop additional public recommendations if needed. 1Find @SDAPCD on X, Facebook, and Instagram
|
Additional recommendations for schools
|
Purple
| Many people could experience serious, lasting adverse health effects. First responders will evaluate for safety and potential shelter in place or evacuation order. |
|
Frequently Asked Questions
Hydrogen sulfide (H2S) is a colorless gas that has a very strong odor (like “rotten egg”). This odor can cause brief mild to moderate symptoms in some individuals, even at very low detection levels.
Several factors are considered when level(s) for ppB would be a concern. Factors include environmental changes, such as temperature, wind, humidity, and time of the year; available data/history of H2S levels to review patterns in frequency, average, and duration; coordination with local/state/federal agencies to evaluate the increased levels and provide recommendations; and other factors to ensure the public receives accurate information. The public will be notified if additional action is needed.
ATSDR has the following resources available:
• Hydrogen Sulfide Frequently Asked Questions: https://www.atsdr.cdc.gov/toxfaqs/tfacts114.pdf
• Environmental Odors Fact Sheet: https://www.atsdr.cdc.gov/odors/docs/are_environmental_odors_toxic_508.pdf
A part per billion (ppB) is a way of measuring the amount of hydrogen sulfide or other things in the air and is smaller than a part per million (ppM). For reference, 1 ppB is equivalent to a single drop of water in a 10,000-gallon pool or 1 penny in a stack of pennies 932 miles high.
Monitors are currently located at Berry Elementary School in the community of Nestor, at the San Diego Fire Station #29 in the community of San Ysidro, and at the Imperial Beach Civic Center.
At this time, H2S levels detected by SDAPCD’s community-based monitors may cause symptoms in people sensitive to the odor. However, there is no scientific evidence to suggest that exposure to the odor will cause lasting impacts to a person’s health. H2S odor can cause symptoms such as headaches and irritation in the eyes, nose, throat, and lungs. These symptoms may follow with dizziness, nausea, vomiting, or abdominal discomfort. Symptoms are expected to resolve when the odor goes away or when the person is in an area where the odor is not present.
For people with pre-existing lung or heart conditions, such as asthma, Chronic Obstructive Pulmonary Disease (COPD), or heart disease, symptoms can be more severe or more frequent. If symptoms persist or worsen, seek medical attention. Take added steps to reduce exposure to the odor, such as by limited outdoor activity, and the use of a heating, ventilation, and air conditioning (HVAC) system or air purifier(s) (with filters that have activated carbon and, if possible, potassium permanganate).
Many reasons can cause the strength of the odor to change on a given day. Examples include the amount of flow of untreated sewage in the Tijuana River, how close a person is to the flow of untreated sewage, temperature, wind speed/direction, humidity, and other environmental factors.
No, SDAPCD does not have the ability to forecast odors in the Tijuana River Valley due to the complex nature of factors that influence the strength of the odors at a given time.
*The public can visit the SDAPCD Tijuana River Valley website to view
current and historical levels of H2S from the Tijuana River Valley.
The website also offers this guidance document in multiple languages.
The following communication and coordination strategies will take
effect for the different threshold levels:
• Green and Yellow
Levels: No notification will be sent for odor in the green and yellow
zones. SDAPCD will continue to monitor H2S levels and post them on the
Tijuana River Valley website.
• Orange Level: For levels in the
orange zone, SDAPCD will post an ‘Odor Advisory’ on the SDAPCD Tijuana
River Valley website, through social media (@SDAPCD on X, Facebook,
and Instagram), SDAPCD email
subscription service, and partner agencies and organizations,
including schools and community-based organizations.
• Purple
Level: For purple zone, first responders will evaluate for safety and
potential shelter in place or evacuation order. Sign up for Alert San Diego to
receive immediate, emergency notifications.
30 ppB was chosen to align with the California Air Resources Board (CARB) H2S threshold of 30 ppB to prevent health impacts connected with foul odor. Per CARB, “if the standard was based on adverse health effects, it would be set at a much higher level.”
Members of the public can check current and historical levels of H2S from the Tijuana River Valley to make informed decisions. The website offers recommended guidance and can be adjusted to suit a person’s individual needs and comfort.
SDAPCD and the County are in communication with affected school districts. School districts have been equipped with guidance to keep children safe and will engage the County and/or SDAPCD with any questions. Please follow the guidance and directions provided by the kid’s school district. Additional resources are available on the County’s school guidance webpage.
H2S and its breakdown products (metabolites) can be measured in blood and urine. However, these measurements are not likely to provide helpful information since H2S and its metabolites leave the body quickly. Measurements of H2S, or its metabolites, in the body cannot predict the kind of health effects that might develop from exposure.
SDAPCD’s mobile app allows anyone to directly report air quality
concerns, such as odors, dust, asbestos, smoke, and others. The mobile
app is available for download at:
• SDAPCD Air Quality
Complaints on the Apple App Store
• SDAPCD Air Quality
Complaints on Google Play
Air quality concerns can also be
reported by phone, at (858) 586-2650, or email, at apcdcomp@sdapcd.org.
For after-hours concerns, please call (858) 586-2650 and select option
2.
Please include the following information when making a
report:
• Your name, address, and telephone number
• The
time and date the air quality concern occurred, and whether the
concern is still present
• The nature of the air quality concern
(smoke, dust, odor, or other)
• The name and address of the
suspected source and the type of operation causing it, if known
SDAPCD is currently measuring hydrogen sulfide, nitrogen dioxide, carbon monoxide, particulate matter less than 10 micrometers, particulate matter less than 2.5 micrometers, black carbon, toxic metals, and toxic volatile organic compounds at the monitoring site in San Ysidro. More information on these pollutants can be found on CARB’s website.
At Berry Elementary School, SDAPCD is currently monitoring H2S. SDAPCD has the ability to periodically collect an instantaneous sample to determine toxic volatile organic compounds during time periods of elevated complaints/odor.