Frequently Asked Questions


A combination of monitoring methods to assess pollutants of primary concern (PM10 and PM2.5) will be conducted in the adjacent areas of the facility during the startup of the ExxonMobil FCCU (Fluid Catalytic Cracking Unit). South Coast AQMD has deployed particulate monitors in advance of the startup to measure and assess air quality for PM10 and PM2.5.  This information is available in real-time from two fixed monitoring locations using monitors that will measure for PM10 and PM2.5.  South Coast AQMD has published information on regarding aspects of predicted impacts and litigation with ExxonMobil Refinery and the two locations are within the areas that are predicted to have the most impacts.  South Coast AQMD does not expect pollutant levels to exceed health thresholds during the startup event at the refinery.  The fixed site measurements will be supplemented with mobile platform measurements that will be conducted in the areas immediately adjacent to the facility during the FCCU startup process.

General FAQ

  • Where is the monitor(s) located for this study?
    The FCCU is located on site at the ExxonMobil Refinery in Torrance, located south of the 405 at Crenshaw Blvd. & 190th st.  Site 1 is located within the facility, while site 2 is located ¼ mile north of the facility.  A map of the location is displayed on the real-time monitoring webpage (select the ExxonMobil monitoring sites from the Monitoring Site drop-down in the upper right corner of the screen).

Does South Coast AQMD measure other pollutants at this site?

  • Yes.  Data from the fixed monitoring sites provided on this website will serve as the most reliable sources for health impacts.  Mobile monitoring, remote sensing, and source testing data give good information on the gradient/plume dispersion from the source of pollutants at the refinery, but do not give relevant information as to health impacts and/or exceedances of health based.

How is PM2.5 measured at the monitoring site?

  • The instruments deployed at the two fixed sites for this event are MetOne E-BAM model 9800.  Beta Attenuation is a measurement method used for particulates, which basically calculates PM concentration by sensing the accumulation of particulates onto a filter media.  The E-BAM principal of operation is based upon U.S. EPA approved methods but it is designed for quick deployment in PM episodic monitoring.  South Coast AQMD has used such instruments in fire response, and the data serves to help forecasting for unhealthful conditions for impacted communities and fire first responders, but not for regulatory purposes.

NOTE: data published to the website is preliminary and therefore subject to change upon final review.  Data QC and review for the continuous hourly measurement are performed later to confirm the validity of the measurements, and this process follows the EPA guidelines for data handling.  Preliminary data is subject to automatic QC routines, which filter out bad data caused by power failure and instrument malfunction.

For finalized/official data, please contact South Coast AQMD Public Records Unit and submit a Public Records Request:

What types of sources contribute to PM2.5 pollution in the atmosphere?

  • While the PM2.5 concentration can be affected by dozens of natural and man-made sources, a significant portion of PM2.5 comes from combustion processes of automobiles, trucks, and stationary sources.  Although a specific source cannot be distinguished from other contributors with this monitor alone, other data sources such as meteorology and activity data can help to assess contributions from various sources, including the ExxonMobil Refinery startup activity.  The sites chosen for the fixed site monitors make the refinery the most likely contributor if elevated PM concentrations are observed.

What is the Federal Standard for PM2.5?

  • PM2.5 is a Federal Criteria Pollutant, which is categorized for known impacts on human health.  Although PM2.5 pollution is small, it can end up deeper in the lungs and have more severe effects than larger dust that is usually removed in the upper respiratory system of humans.  The EPA uses PM2.5 mass concentration (micrograms per cubic meter) in the National Ambient Air Quality Standards (NAAQS) as follows:

Primary standard (for protection of human health): 12 µg/m3 Annual Arithmetic Mean, averaged over 3 years

Secondary Standard (for protection of environmental quality and visibility): 15 µg/m3 Annual Arithmetic Mean, averaged over 3 years

Primary and Secondary: 35 µg/m3 (24-hour average), 98th Percentile Value averaged over 3 years

For more information on PM pollution, please visit to external website. for basic information and technical documents on PM regulation and monitoring programs under the EPA.


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