Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published April 27, 2019 | Published
Journal Article Open

Optical Properties and Radiative Forcing of Aged BC due to Hygroscopic Growth: Effects of the Aggregate Structure

Abstract

Black carbon (BC) particles become hydrophilic after mixing with soluble matter in the atmosphere, and their optical and radiative properties can be significantly modified accordingly. This study investigates the impact of aggregate structure on optical and radiative properties of aged BC, that is, BC coated by sulfate or organic aerosols, especially during hygroscopic growth. A more realistic BC morphology based on fractal aggregates is considered, and inhomogeneous mixtures of BC aggregates are treated more realistically (with respect to particle geometries) in the multiple sphere T‐matrix method for optical property simulations. As relative humidity increases, BC extinction is significantly enhanced due to an increase in scattering, and the enhancement depends on the amount and hydrophilicity of the coating. The absorption exhibits less variation during hygroscopic growth because the coating of aerosols already leads to BC absorption close to the maximum. Furthermore, hygroscopic growth not only results in negative radiative forcing (RF) at the top of the atmosphere but also slightly weakens the absorption in the atmosphere (inducing a negative RF in the atmosphere). Compared to the more realistic model with BC as aggregates, the currently popular core‐shell model reasonably approximates the top of the atmosphere RF but underestimates the atmospheric RF due to hygroscopic growth by up to 40%. Furthermore, for the RF caused by internal mixing, the core‐shell model overestimates the RFs at the surface and in the atmosphere by ~10%.

Additional Information

© 2019 American Geophysical Union. Received 13 OCT 2018; Accepted 25 MAR 2019; Accepted article online 2 APR 2019; Published online 17 APR 2019. We particularly thank D. M. Mackowski and M. I. Mishchenko for the MSTM code (http://eng.auburn.edu/users/dmckwski/scatcodes/), and Paul Ricchiazzi for the SBDART code (https://www.paulschou.com/tools/sbdart/). All data related to this work are available online (https://github.com/Zeng86/Hygroscopic‐growth‐data). This work was financially supported by the National Key Research and Development Program of China (2016YFA0602003), the National Natural Science Foundation of China (NSFC) grants 41571348 and 41590873, and the Young Elite Scientists Sponsorship Program by CAST (2017NRC001).

Attached Files

Published - Zeng_et_al-2019-Journal_of_Geophysical_Research__Atmospheres.pdf

Files

Zeng_et_al-2019-Journal_of_Geophysical_Research__Atmospheres.pdf
Files (1.8 MB)

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023