Composition and hygroscopicity of the Los Angeles Aerosol: CalNex
Author
Hersey, Scott P.
Craven, Jill S.
Metcalf, Andrew R.
Lin, Jack
Lathem, Terry
Suski, Kaitlyn J.
Cahill, John F.
Duong, Hanh T.
Sorooshian, Armin
Jonsson, Haflidi H.
Shiraiwa, Manabu
Zuend, Andreas
Nenes, Athanasios
Prather, Kimberly A.
Flagan, Richard C.
Seinfeld, John H.
Date
2013Metadata
Show full item recordAbstract
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.
Description
The article of record as published may be found at http://dx.doi.org/10.1002/jgrd.50307
Journal of Geophysical Research-Atmospheres, Vol. 118, pp. 3016-3036
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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