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Satellite study suggests California clean air regulations working to reduce PM2.5 emissions in state

Scientists from Emory University, NASA’s Jet Propulsion Laboratory and the California Air Resources Board teamed to analyze satellite data to determine the 15-year trend of PM2.5 pollution in the state. PM2.5 is especially burdensome in California and accounts for the greatest percentage of health impacts attributable to air pollution.

The open-access study, which focused on the four major components of PM2.5 to predict PM2.5 species, was recently published in the journal Atmospheric Environment. This study is the first attempt to use the Multi-angle Imaging SpectroRadiometer (MISR) aerosol sensors aboard NASA’s Terra satellite to predict PM2.5 sulfate, nitrate, OC and EC concentrations at the sub-regional scale.

Most monitors do not track individual PM2.5 components, and monitors are mainly placed in urban areas where traffic is heaviest and more people live, not in rural areas. The satellite technology fills spatial and temporal gaps in air quality data.

The study demonstrates the success of California’s air pollution control programs, regulations, enforcement efforts and clean-air plans in regions with the greatest air quality challenges: Southern California and the southern Central Valley.

MISR Maps_0
Maps of 3-year averaged PM2.5 sulfate, nitrate, OC and EC concentrations estimated using 4.4 km-resolution MISR aerosol properties over Southern California for years 2001–2003, 2007–2009 and 2013–2015. LA=Los Angeles basin, CV=Central Valley, OC=Organic Carbon, EC=Elemental Carbon. Click to enlarge.

Satellite data was able to identify locations that could be directly linked to programs that reduced measured pollutants:

  • Coastal Cities: Concentrations of sulfates in coastal cities decreased significantly, the result of CARB’s 2006 ultra-low sulfur diesel fuel standard, 2007 Drayage Truck Rule, and 2008 Ocean-Going Vessel Fuel Regulation.

  • Transportation Corridors in Los Angeles: Concentrations of nitrates in the Los Angeles area decreased significantly, most prominently near transportation corridors, pointing to the success of CARB’s various mobile source NOx control programs.

  • Urban and Suburban Southern California: Concentrations of organic carbon (OC) and elemental carbon (EC) decreased significantly in both the urban and suburban areas of Southern California. This is the result of CARB’s programs that clean up cars and trucks, along with other programs including wood burning rules implemented by air districts.

In the future, satellite remote sensing technology can be used to identify air pollution “hotspots” of major components of fine particle pollution, and help inform air quality management strategies and public health surveillance programs.

The MISR instrument used in the study was initially designed to help understand Earth’s climate. To determine how the climate may be changing, researchers need to know the amount of sunlight that is scattered in different locations around the globe. Unlike most satellite instruments that look only straight down, or toward the edge of the planet, MISR views Earth with cameras pointed at nine different angles. MISR has other applications, including the ability to distinguish between different types of particle pollution. For this MISR study, researchers built mathematical models linking chemical composition data with specific satellite signals.

Launched in December 1999 with a planned six-year mission life, MISR was built and is operated by JPL for NASA’s Science Mission Directorate in Washington, DC. The Terra spacecraft is operated by NASA’s Goddard Space Flight Center, Greenbelt, Maryland. MISR and Terra are currently in their 19th year of operation.


  • Xia Meng, Michael J. Garay, David J. Diner, Olga V. Kalashnikova, Jin Xu, Yang Liu (20180) “Estimating PM2.5 speciation concentrations using prototype 4.4 km-resolution MISR aerosol properties over Southern California,” Atmospheric Environment, Volume 181, Pages 70-81 doi: 10.1016/j.atmosenv.2018.03.019


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