State of Carbonaceous Aerosols in California


Researchers, including U.S. Department of Energy scientists from Pacific Northwest National Laboratory, used two aircraft-based field campaigns to
understand the distribution and mixing state of carbonaceous aerosols in California. One campaign sampled aerosols over southern California to understand the role of particle composition on air quality and climate change. The other campaign followed the evolution of organics and soot as urban emissions were transported from Sacramento into the Sierra Nevada foothills. These studies, conducted in May and June 2010, assessed the particle mixing state throughout most of California. Even though atmospheric particle composition in both regions was influenced by urban sources, the mixing state was found to vary greatly. Nitrate and soot were the dominant species in southern California, while sulfate and organics were more prevalent in northern California. The mixing state varied temporally in northern California, where soot mixed with organics became the prevalent particle type toward the end of the study as regional pollution levels increased. Nearly 97% of submicron particles contained carbonaceous material, and nearly 88% of all particles sampled showed signs of atmospheric aging. These studies demonstrate that the majority of ambient carbonaceous particles in California are internally mixed and heavily influenced by the secondary species that are most prevalent in this particular region. Considerations of regionally dominant sources and secondary species, as well as temporal variations of aerosol physical and optical properties, will be required to obtain more accurate predictions of aerosol climate impacts in California and elsewhere.


Cahill, J. F., K. Suski, J. H. Seinfeld, R. A. Zaveri, and K. A. Prather. 2012. “The Mixing State of Carbonaceous Aerosol Particles in Northern and Southern California Measured During CARES and CalNex 2010,” Atmospheric Chemistry and Physics 12, 10989–11002. DOI: 10.5194/acp-12-10989-2012, 2012.