Ultrafine Particulate Matter

Learn about the Air District’s special purpose ultrafine particulate matter monitoring project.

Ultrafine particulate matter (UFP) refers to particles with diameters less than 0.1 microns. They have known adverse health effects. Currently they are not regulated by the United States Environmental Protection Agency. Thus air districts are not required to monitor UFP.

The Bay Area Air Quality Management District recognizes that monitoring UFP levels in the Bay Area, identifying their emission sources and assessing their health impacts are important. In 2011, the Air District established a comprehensive program to study UFP. As part of this program, the Air District began making measurements at four air monitoring stations – Santa Rosa (now Sebastopol), San Pablo, Livermore, and Redwood City. The number of measurement sites has since increased to include Oakland (Laney College) and San Jose, with Berkeley expected to be online soon. These newer locations are part of a near-roadway measurement effort. At each station, the number of particles in a specified volume of air is counted every second.

In addition to the number counts, sampling began in 2015 at two stations to gather data on UFP composition. The Air District funds a station at San Pablo. The California Air Resources Board funds a site in East Oakland. Collected samples are analyzed for nineteen metals. These analyses are done by UC Davis, a contractor to both agencies. Data obtained from these measurements will be used to identify major UFP sources in the Bay Area, evaluate models and refine estimates of UFP’s public health impact.

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Last Updated: 3/24/2021