Evolution of aerosol composition and optical properties during the 2010 CARES campaign
Authors
Rahul Zaveri — Pacific Northwest National Laboratory
William Patrick Arnott — University of Nevada Reno
Dean Bruce Atkinson — Portland State University
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Josef Beranek — Pacific Northwest National Laboratory
Jack Cahill — University of California, San Diego
Chris Cappa — University of California, Davis
Duli Chand — Pacific Northwest National Laboratory
Daniel James Cziczo — Massachusetts Institute of Technology
Manvendra K. Dubey — Los Alamos National Laboratory
Matt Erickson — Washington State University
Jerome D Fast — Pacific Northwest National Laboratory
Cody Floerchinger — Montana State University
Bradley Flowers — Los Alamos National Laboratory
Kyle Gorkowski — Los Alamos National Laboratory
Madhu Gyawali — Desert Research Institute
John Hubbe — Pacific Northwest National Laboratory
Bertram Tom Jobson — Washington State University
Evgueni Kassianov — Pacific Northwest National Laboratory
Larry Kleinman — Brookhaven National Laboratory
Walter Berkett Knighton — Montana State University
Nels S Laulainen — Pacific Northwest National Laboratory
Claudio Mazzoleni — Michigan Technological University
Mikhail S. Pekour — Pacific Northwest National Laboratory
Kimberly Prather — Scripps Institution of Oceanography
Jimmy Radney — National Institute of Standards and Technology (NIST)
William J. Shaw — Pacific Northwest National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
R. Subramanian — Carnegie Mellon University
Arthur J Sedlacek — Brookhaven National Laboratory
Ari Setyan — University of California, Davis
Chen Song — Pacific Northwest National Laboratory
Kaitlyn Suski — University of California, San Diego
Will Wallace — Washington State University
Xiao-Ying Yu — Pacific Northwest National Laboratory
Alla Zelenyuk-Imre — Pacific Northwest National Laboratory
Qi Zhang — University of California, Davis
Category
Field Campaigns
Description
Atmospheric black carbon (BC) particles readily absorb both upwelling and downwelling broadband radiation and are thought to be second only to CO2 in contributing to global warming. However, large uncertainties still exist in the global estimates of BC radiative forcing, which depend not only on our ability to accurately simulate the global loading and distribution of BC, but also on the precise knowledge of the mixing state and morphology of BC particles due to ageing. To this end, one of the objectives of the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted in Sacramento, California, during June 2010 was to investigate the evolution of urban BC particles and the associated optical properties, with the overarching goal of improving their process-level model representations. The daytime Sacramento urban plume was routinely transported to the northeast into the Sierra Nevada foothills area rich in biogenic emissions, and the aged aerosols were often recirculated back into the urban area the next morning. The CARES campaign observational strategy was designed to take advantage of this flow pattern by setting up two observation supersites—one located within the Sacramento urban area and another located about 24 km to the northeast in Cool, California, a small town in the rural foothills area. The DOE G-1 aircraft was also deployed in the morning and afternoon on selected days to characterize the evolution of urban and biogenic aerosols and their optical properties.
In this study, we present the analysis of the measurements made at the two ground sites and onboard the aircraft to illustrate the evolution of aerosol composition and optical properties due to ageing. Results indicate up to 30% enhancement in BC mass absorption efficiency (at 532 nm wavelength) due to BC ageing. Angstrom exponents for absorption were found to be appreciably greater than unity at low aerosol loadings, suggesting presence of “brown carbon” in background air. Single-particle mass spectrometer data onboard the G-1 and at the ground sites indicate that biomass burning particles were present in appreciable amounts, which could at least partially explain the source of brown carbon. Sensitivity of the predicted optical properties with the core/shell Mie code to model assumptions of particle mixing state will be discussed.