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Published April 20, 2012 | Published
Journal Article Open

Black carbon aerosol over the Los Angeles Basin during CalNex


Refractory black carbon (rBC) mass and number concentrations were quantified by a Single Particle Soot Photometer (SP2) in the CalNex 2010 field study on board the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter in the Los Angeles (LA) Basin in May, 2010. The mass concentrations of rBC in the LA Basin ranged from 0.002–0.530 μg m^(−3), with an average of 0.172 μg m^(−3). Lower concentrations were measured in the Basin outflow regions and above the inversion layer. The SP2 afforded a quantification of the mixing state of rBC aerosols through modeling the scattering cross-section with a core-and-shell Mie model to determine coating thickness. The rBC particles above the inversion layer were more thickly coated by a light-scattering substance than those below, indicating a more aged aerosol in the free troposphere. Near the surface, as the LA plume is advected from west to east with the sea breeze, a coating of scattering material grows on rBC particles, coincident with a clear growth of ammonium nitrate within the LA Basin and the persistence of water-soluble organic compounds as the plume travels through the outflow regions. Detailed analysis of the rBC mixing state reveals two modes of coated rBC particles; a mode with smaller rBC core diameters (∼90 nm) but thick (>200 nm) coating diameters and a mode with larger rBC cores (∼145 nm) with a thin (<75 nm) coating. The "weekend effect" in the LA Basin results in more thickly coated rBC particles, coinciding with more secondary formation of aerosol.

Additional Information

© 2012 American Geophysical Union. Received 1 December 2011; accepted 14 March 2012; published 20 April 2012. This work was supported by NOAA grant NA09OAR4310128. The authors wish to thank Greg Kok at DMT and Anne Perring and Joshua (Shuka) Schwarz at NOAA for their guidance on data analysis and calibration. We also acknowledge the entire CIRPAS crew for their professionalism and assistance during the campaign.

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Published - Metcalf2012p18187J_Geophys_Res-Atmos.pdf


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