Hydrogen sulfide levels by weekly average

Weekly averages show levels above state and federal thresholds for chronic inhalation exposure. To be considered chronic, conditions must be consistent for at least one year.

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The San Ysidro monitor went online first, followed by Nestor and then Imperial Beach. There is a gap in San Ysidro data because of equipment problems.

Source: The San Diego County Air Pollution Control District

Michelle Guerrero / The San Diego Union-Tribune