Fine Particulate Air Pollution Monitoring Program
Health and Safety Code, Section 39619.5(g) requires the California Air Resources Board (CARB) to provide an update each year on the status and results of the fine particulate matter (PM2.5) monitoring program.
California’s PM2.5 air quality monitoring program provides information used for determining which areas violate PM2.5 standards, characterizing the sources that contribute to PM2.5 pollution, determining background concentrations, assessing pollution transport, and supporting health studies and other research. Monitoring data also provide information to develop and evaluate programs for improving air quality. Newly emerging technologies are evaluated and incorporated continuously in California’s PM2.5 monitoring program to provide improved monitoring data.
California’s PM2.5 regulatory monitoring network, jointly operated by CARB and the local air districts, began collecting data in 1998. A number of different types of PM2.5 regulatory monitors are operated to provide data on PM2.5 mass and chemical composition which are summarized below. The type and number of PM2.5 regulatory monitors in operation has changed from year to year depending upon programmatic needs and available funding.
PM2.5 Monitoring Network
The PM2.5 monitoring network consists of sites owned and operated by State, Local, and Tribal monitoring agencies and is comprised of manual Federal Reference Methods (FRMs) and automated continuous Federal Equivalent Methods (FEMs). The primary use of both types of methods is to assess compliance with the PM2.5 National Ambient Air Quality Standards (NAAQS). Since continuous FEMs are automated, they are also readily used to support forecasting and reporting of PM2.5 in the Air Quality Index (AQI). The requirements for monitoring PM2.5 can be found in 40 CFR part 58 Appendix D.
PM2.5 monitoring sites are to be population-oriented, measuring exposures where people live, work, and play. For comparison to the annual PM2.5 standard, the locations must be community-oriented and as such, these do not necessarily correspond to the locations of highest PM concentrations in an area. Existing Metropolitan Statistical Areas are first examined to determine where the majority of the people live in each state. These are then broken down into smaller populated entities which may include county, zip code, census tract, or census block boundaries. Combinations of these population entities are combined to define Metropolitan Planning Areas. These may be further sub-divided into Community Monitoring Zones, based on examination of existing PM measurements, source locations, terrain, and meteorology. Finally, PM2.5 monitors are located at specific sites that represent neighborhood or urban scales to determine compliance with the annual standard and at maximum, population oriented locations for comparison with the 24-hour standard. Transport and background sites are located between and away from planning areas to determine regional increments to PM measured within the planning area.
- Quality Assurance Air Monitoring Information - The Quality Assurance Air Monitoring site provides information on all sites in California that are audited by CARB's Quality Assurance Section.
- Ambient Air Quality Monitoring - The Air Quality Monitoring site provides information on California's extensive air monitoring program, including links to ambient air quality monitoring, the Community Air Protection Program, and a pollution mapping tool for local communities, as well as a link to real-time and historical air quality data.
- Annual Network Plan - U.S. EPA requires the annual submission of an plan providing detailed information about criteria pollutant monitoring sites and the instruments operating at those sites. These plans cover monitoring activity occurring in the previous year as well as potential upcoming changes to the local district and State networks.
FRM PM2.5 monitors rely on weighing PM2.5 collected on filters. Measurement of PM2.5 in the air has evolved over time as new instruments have been developed. FEM PM2.5 monitors, for example, continuously measure PM2.5 mass concentration using more recently developed measurement technologies. PM2.5 non-regulatory monitors are not used to provide PM2.5 data for regulatory purposes primarily due to not meeting federal monitoring requirements.
Federal Reference Method (FRM) Monitors
The installation of federally-approved PM2.5 mass monitors throughout California began in 1998. FRM monitors are operated at sites throughout California. These monitors collect particulate samples on filters, later weighed and analyzed in a laboratory. Because of this two-step process, PM2.5 air quality data collected with FRM monitors are not immediately available. This approach is more labor intensive and provides less temporal resolution than the continuous PM2.5 mass monitors CARB began to add to the network in the late 1990s.
Federal Equivalent Method (FEM) Monitors
Continuous PM2.5 monitors provide valuable information for public reporting on PM2.5 concentration levels, temporal representation, health studies, transport studies, and background monitoring. The primary continuous monitor in use in California is the Beta Attenuation Monitor (BAM). Several other types of continuous monitors (e.g., laser light scattering monitors) are also used in a limited capacity. The U.S. EPA designated certain models of continuous monitors as Federal Equivalent Method (FEM) monitors. Since these monitors are considered equivalent to the FRM monitors, they can be used to determine compliance with federal standards. In addition to being less labor intensive than filter-based methods, continuous concentration monitors provide data at an hourly temporal resolution.
Another major stage of network implementation is the deployment of PM2.5 speciation monitors. Speciation monitoring provides valuable information about the composition, and ultimately, the sources of PM2.5 pollution.
There are two components to the PM2.5 speciation network in California. The first component, mandated by the U.S. EPA, requires filter-based PM2.5 speciation monitoring at seven California sites that are now part of the National Speciation Trends Network (STN) for PM2.5 speciation. The sites were selected based on a balance of many factors including location of an existing PAMS monitor, size of the urban area, and ozone and PM10 nonattainment status. These monitors are also part of the Chemical Speciation Network (CSN) that are used to assess trends, develop state implementation plans, develop emission control strategies, track control program progress, aid in interpreting health studies, characterize seasonal and spatial variations of PM2.5 pollution. These monitors are located in Bakersfield (San Joaquin Valley), El Cajon (San Diego), Fresno (San Joaquin Valley), Los Angeles (South Coast), Riverside (South Coast), Sacramento (Sacramento Valley), and San Jose (San Francisco Bay Area).
The second component of California’s PM2.5 speciation network is the deployment of samplers at CSN sites located at selected State and Local Air Monitoring Stations (SLAMS). Data from these sites provide additional information needed for developing effective air quality attainment plans. CARB and local air districts operate these filter-based speciation monitors at seven sites - Calexico (Imperial Valley), Chico (Butte County), Mammoth Lakes (Great Basin Valleys), Modesto (San Joaquin Valley), Portola (Northern Sierra), Sacramento (Sacramento Valley), and Visalia (San Joaquin Valley).
In 2007, CARB began monitoring for specific wood smoke tracers to determine the contribution of wood burning sources to PM2.5 levels. Wood smoke tracers are being monitored during the winter season at all six of the State and Local CSN sites - Calexico, Chico, Modesto, Portola, Sacramento, and Visalia.
Accessing PM2.5 Data
Data collected as part of California’s PM2.5 monitoring program may be obtained in several ways. Daily PM2.5 values as well as summary statistics can be accessed at iADAM: Air Quality Data Statistics.
Real-time hourly PM2.5 data from California’s continuous monitors can also be found at Air Quality and Meteorological Information System (AQMIS).
AQview is a new community-focused air quality monitoring data portal bringing together many data sources across the State. The AQview Continuous Monitoring Download Tool is providing access to community air quality data This information can be found at AQview - Air Quality Viewer.
Use of PM2.5 Data
Data collected as part of the PM2.5 monitoring program is used by policy makers, regulators, researchers, community groups, and individual citizens. A few of the countless uses of PM2.5 data at CARB include: