Constraining the particle-scale diversity of black carbon light absorption using a unified framework
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Published:2022-11-22
Issue:22
Volume:22
Page:14825-14836
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Beeler PaytonORCID, Chakrabarty Rajan K.ORCID
Abstract
Abstract. Atmospheric black carbon (BC), the strongest absorber of
visible solar radiation in the atmosphere, manifests across a wide spectrum
of morphologies and compositional heterogeneity. Phenomenologically, the
distribution of BC among diverse particles of varied composition gives rise
to enhancement of its light absorption capabilities by over twofold in
comparison to that of nascent or unmixed homogeneous BC. This situation has
challenged the modeling community to consider the full complexity and
diversity of BC on a per-particle basis for accurate estimation of its light
absorption. The conventionally adopted core–shell approximation, although
computationally inexpensive, is inadequate not only in estimating but also
capturing absorption trends for ambient BC. Here we develop a unified
framework that encompasses the complex diversity in BC morphology and
composition using a single metric, the phase shift parameter (ρBC),
which quantifies how much phase shift the incoming light waves encounter
across a particle compared to that in its absence. We systematically
investigate variations in ρBC across the multi-space distribution of
BC morphology, mixing state, mass, and composition as reported by field and
laboratory observations. We find that ρBC>1 leads to
decreased absorption by BC, which explains the weaker absorption
enhancements observed in certain regional BC compared to laboratory results
of similar mixing state. We formulate universal scaling laws centered on
ρBC and provide physics-based insights regarding core–shell
approximation overestimating BC light absorption. We conclude by packaging
our framework in an open-source Python application to facilitate
community-level use in future BC-related research. The package has two main
functionalities. The first functionality is for forward problems, wherein
experimentally measured BC mixing state and assumed BC morphology are input,
and the aerosol absorption properties are output. The second functionality
is for inverse problems, wherein experimentally measured BC mixing state and
absorption are input, and the morphology of BC is returned. Further, if
absorption is measured at multiple wavelengths, the package facilitates the
estimation of the imaginary refractive index of coating materials by combining
the forward and inverse procedures. Our framework thus provides a
computationally inexpensive source for calculation of absorption by BC and
can be used to constrain light absorption throughout the atmospheric
lifetime of BC.
Funder
Energy Frontier Research Centers National Science Foundation
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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