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Composition and hygroscopicity of the Los Angeles Aerosol: CalNex

Hersey, Scott P. and Craven, Jill S. and Metcalfe, Andrew R. and Lin, Jack and Lathem, Terry and Suski, Kaitlyn J. and Cahill, John F. and Duong, Hanh T. and Sorooshian, Armin and Jonsson, Haflidi H. and Shiraiwa, Manabu and Zuend, Andreas and Nenes, Athanasios and Prather, Kimberly A. and Flagan, Richard C. and Seinfeld, John H. (2013) Composition and hygroscopicity of the Los Angeles Aerosol: CalNex. Journal of Geophysical Research. Atmospheres, 118 (7). pp. 3016-3036. ISSN 2169-897X. doi:10.1002/jgrd.50307.

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Aircraft-based measurements of aerosol composition, either bulk or single-particle, and both subsaturated and supersaturated hygroscopicity were made in the Los Angeles Basin and its outflows during May 2010 during the CalNex field study. Aerosol composition evolves from source-rich areas in the western Basin to downwind sites in the eastern Basin, evidenced by transition from an external to internal mixture, as well as enhancements in organic O : C ratio, the amount of organics and nitrate internally mixed on almost all particle types, and coating thickness on refractory black carbon (rBC). Transport into hot, dilute outflow regions leads to significant volatilization of semivolatile material, resulting in a unimodal aerosol comprising primarily oxygenated, low-volatility, water-soluble organics and sulfate. The fraction of particles with rBC or soot cores is between 27 and 51% based on data from a Single Particle Soot Photometer (SP2) and Aerosol Time of Flight Mass Spectrometer (ATOFMS). Secondary organics appear to inhibit subsaturated water uptake in aged particles, while CCN activity is enhanced with photochemical age. A biomass-burning event resulted in suppression of subsaturated hygroscopicity but enhancement in CCN activity, suggesting that BB particles may be nonhygroscopic at subsaturated RH but are important sources of CCN. Aerosol aging and biomass burning can lead to discrepancies between subsaturated and supersaturated hygroscopicity that may be related to mixing state. In the cases of biomass burning aerosol and aged particles coated with secondary material, more than a single parameter representation of subsaturated hygroscopicity and CCN activity is needed.

Item Type:Article
Related URLs:
URLURL TypeDescription
Metcalfe, Andrew R.0000-0003-0385-1356
Lin, Jack0000-0002-4453-1263
Suski, Kaitlyn J.0000-0001-5183-7335
Sorooshian, Armin0000-0002-2243-2264
Jonsson, Haflidi H.0000-0003-3043-1074
Shiraiwa, Manabu0000-0003-2532-5373
Zuend, Andreas0000-0003-3101-8521
Nenes, Athanasios0000-0003-3873-9970
Prather, Kimberly A.0000-0003-3048-9890
Flagan, Richard C.0000-0001-5690-770X
Seinfeld, John H.0000-0003-1344-4068
Additional Information:© 2013 American Geophysical Union. Received 2 July 2012; revised 24 January 2013; accepted 21 February 2013; published 11 April 2013. This work was supported by NOAA grant NA09OAR4310128 and CARB agreement #09-333.
Funding AgencyGrant Number
National Oceanic and Atmospheric Administration (NOAA)NA09OAR4310128
California Air Resources Board09-333
Subject Keywords:urban aerosol; hygroscopicity; CCN; CalNex
Issue or Number:7
Record Number:CaltechAUTHORS:20130712-102252597
Persistent URL:
Official Citation:Hersey, S. P., et al. (2013), Composition and hygroscopicity of the Los Angeles Aerosol: CalNex, J. Geophys. Res. Atmos., 118, 3016–3036, doi:10.1002/jgrd.50307.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39339
Deposited On:12 Jul 2013 20:00
Last Modified:24 Feb 2023 23:51

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