Latest News

September 16, 2025

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On September 10, 2025, at approximately 4:00 a.m., the benzene level measured by community monitor MS-07 was 10.06 ppb. This reading is above the acute Reference Exposure Level (REL) of 8 ppb. The measurement for the hour following this elevated reading returned to regional background levels. After a preliminary investigation by SCS Engineers, Tricorntech (the instrument manufacturer), and South Coast AQMD, it was determined this elevated measurement was caused by a faulty calibration gas valve. The malfunction appears to have contaminated the sample following a routine quality control check on the instrument. The same valve issue is believed to be responsible for a similarly elevated measurement of 7.33 ppb observed on September 7th at 4:00 a.m. A technical report detailing these findings will follow.

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August 2, 2025

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On August 2, 2025, at around 5 pm, the benzene level measured by fenceline monitor MS-01 was 27.4 ppb. This reading is above the acute Reference Exposure Level (REL) of 8 ppb. After discussion with SCS Engineers and the instrument manufacturer, and an in-depth analysis of the available data, it was determined this exceedance event was caused by instrument instability, and the data is considered invalid. The same instrument issue was responsible for the slightly elevated levels of toluene and THF that were observed around the same time. SCS has since serviced the instrument to prevent this from recurring. Notably, at the time of this reading, none of the community monitoring sites recorded an increase in benzene or other measured pollutants. A technical report detailing the rationale for invalidating this data is linked below.

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‍We are seeking input from the community on how to improve this and future reports. Should you have any comments or feedback on the format and/or content of this report, please contact Dr. Andrea Polidori at apolidori@aqmd.gov.

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Analysis of Elevated Benzene Levels – July 29 and August 2, 2025

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