Open AccessBlack carbon aerosol over the Los Angeles Basin during CalNex
Author(s) -
Metcalf A. R.,
Craven J. S.,
Ensberg J. J.,
Brioude J.,
Angevine W.,
Sorooshian A.,
Duong H. T.,
Jonsson H. H.,
Flagan R. C.,
Seinfeld J. H.
Publication year - 2012
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jd017255
Subject(s) - aerosol , plume , soot , carbon black , mie scattering , outflow , troposphere , scattering , structural basin , atmospheric sciences , environmental science , mineralogy , geology , materials science , chemistry , light scattering , meteorology , oceanography , optics , physics , geomorphology , composite material , natural rubber , organic chemistry , combustion
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 μ g m −3 , with an average of 0.172 μ g 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.