Air Quality during ExxonMobil Restart did not exceed Health Thresholds

May 10, 2016

Air monitoring in the community next to the ExxonMobil refinery during its restart activities last night showed that fine particulate levels did not exceed any health-based thresholds.

“The conditions requested by the South Coast Air Quality Management District and adopted by our Hearing Board imposed strict limits on emissions during the refinery startup,” said Wayne Nastri, SCAQMD’s acting executive officer.

“Our analysis predicted that no health-based thresholds would be exceeded during the startup and our continuous air monitoring has shown that to be the case.”

SCAQMD air monitoring scientists and field inspectors have been present in and around the refinery since yesterday afternoon, focusing on a predicted six-hour period when ExxonMobil planned to turn off a major pollution control system as a safety measure.

ExxonMobil was able to shorten the time needed for the shutdown to less than three hours; the system was shut off after 8:30 p.m. yesterday and restarted at about 11:30 p.m. yesterday. The system, called an electrostatic precipitator, will now operate continuously as the refinery resumes normal operations.

Four SCAQMD continuous air monitors at two locations – inside the refinery property and in the community near the facility – did not show any levels of fine particulate pollution that exceeded health-based thresholds. During the past 24 hours, the highest level recorded at these sites was a one-hour average of PM10 of 43 micrograms per cubic meter (ug/m3) at 10 a.m. today.

The state health-based standard for PM10 averaged over 24 hours is 50 ug/m3, and the federal standard is 150 ug/m3 during a 24-hour average. A one-hour concentration above these levels does not constitute an exceedance of a health threshold. 

SCAQMD also monitored PM2.5 levels, which were even lower than PM10 values.

Residents can view these results at (In the upper right-hand corner of the web page, click on the drop down box and select one of the options labeled “ExxonMobil”.) For more information on SCAQMD’s air monitoring at these sites, see the FAQ at

SCAQMD staff also drove two vehicles equipped with fine particulate monitors through the community and none of the levels recorded exceeded health thresholds.

The continuous air quality monitors have been operating since April 29 and will remain in place through tomorrow. SCAQMD staff now is reviewing in detail all conditions of the abatement order to ensure that ExxonMobil complied with all of the order’s conditions during the shutdown of the pollution control device.

The SCAQMD is the air pollution control agency for Orange County and major portions of Los Angeles, San Bernardino and Riverside counties.

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