Black carbon radiative heating effects on cloud microphysics and implications for the aerosol indirect effect. 1. Extended Köhler theory

William C Conant, Athanasios Nenes, John H. Seinfeld

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

Black carbon (BC) aerosol absorbs sunlight that might have otherwise been reflected to space and changes the radiative heating of the atmosphere and surface. These effects may alter the dynamical and hydrological processes governing cloud formation. A new, microphysical, effect of BC on climate is identified here, in which solar heating within BC-containing cloud condensation nuclei (CCN) slows or prevents the activation of these CCN into cloud drops. Solar-heated BC-containing droplets are elevated in temperature by fractions of a degree above the ambient, thus raising the droplet vapor pressure and inhibiting activation of the most absorptive CCN. This paper develops the theory describing the alteration of the Köhler curve (i.e., the equilibrium vapor pressure over a droplet as a function of water uptake) as a function of CCN size and BC fraction. The effect is most significant in those CCN that contain volumes of BC larger than a 500 nm diameter sphere. For an aerosol population with 10% BC mass fraction per particle, solar heating can cause a 10% reduction in the CCN concentration at 0.01% critical supersaturation. On the other hand, the effect of heating by BC absorption on CCN activation above ∼0.1% critical supersaturation is negligible.

Original languageEnglish (US)
Article number4604
JournalJournal of Geophysical Research: Space Physics
Volume107
Issue number21
DOIs
StatePublished - 2002
Externally publishedYes

Fingerprint

Soot
cloud microphysics
black carbon
cloud condensation nucleus
condensation nuclei
Aerosols
aerosols
Condensation
aerosol
heating
Heating
carbon
droplet
Solar heating
solar heating
Chemical activation
Supersaturation
supersaturation
Vapor pressure
vapor pressure

Keywords

  • Black carbon
  • CCN
  • Cloud condensation nuclei
  • Droplet thermodynamics
  • Kohler theory
  • Soot

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Atmospheric Science
  • Astronomy and Astrophysics
  • Oceanography

Cite this

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title = "Black carbon radiative heating effects on cloud microphysics and implications for the aerosol indirect effect. 1. Extended K{\"o}hler theory",
abstract = "Black carbon (BC) aerosol absorbs sunlight that might have otherwise been reflected to space and changes the radiative heating of the atmosphere and surface. These effects may alter the dynamical and hydrological processes governing cloud formation. A new, microphysical, effect of BC on climate is identified here, in which solar heating within BC-containing cloud condensation nuclei (CCN) slows or prevents the activation of these CCN into cloud drops. Solar-heated BC-containing droplets are elevated in temperature by fractions of a degree above the ambient, thus raising the droplet vapor pressure and inhibiting activation of the most absorptive CCN. This paper develops the theory describing the alteration of the K{\"o}hler curve (i.e., the equilibrium vapor pressure over a droplet as a function of water uptake) as a function of CCN size and BC fraction. The effect is most significant in those CCN that contain volumes of BC larger than a 500 nm diameter sphere. For an aerosol population with 10{\%} BC mass fraction per particle, solar heating can cause a 10{\%} reduction in the CCN concentration at 0.01{\%} critical supersaturation. On the other hand, the effect of heating by BC absorption on CCN activation above ∼0.1{\%} critical supersaturation is negligible.",
keywords = "Black carbon, CCN, Cloud condensation nuclei, Droplet thermodynamics, Kohler theory, Soot",
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T1 - Black carbon radiative heating effects on cloud microphysics and implications for the aerosol indirect effect. 1. Extended Köhler theory

AU - Conant, William C

AU - Nenes, Athanasios

AU - Seinfeld, John H.

PY - 2002

Y1 - 2002

N2 - Black carbon (BC) aerosol absorbs sunlight that might have otherwise been reflected to space and changes the radiative heating of the atmosphere and surface. These effects may alter the dynamical and hydrological processes governing cloud formation. A new, microphysical, effect of BC on climate is identified here, in which solar heating within BC-containing cloud condensation nuclei (CCN) slows or prevents the activation of these CCN into cloud drops. Solar-heated BC-containing droplets are elevated in temperature by fractions of a degree above the ambient, thus raising the droplet vapor pressure and inhibiting activation of the most absorptive CCN. This paper develops the theory describing the alteration of the Köhler curve (i.e., the equilibrium vapor pressure over a droplet as a function of water uptake) as a function of CCN size and BC fraction. The effect is most significant in those CCN that contain volumes of BC larger than a 500 nm diameter sphere. For an aerosol population with 10% BC mass fraction per particle, solar heating can cause a 10% reduction in the CCN concentration at 0.01% critical supersaturation. On the other hand, the effect of heating by BC absorption on CCN activation above ∼0.1% critical supersaturation is negligible.

AB - Black carbon (BC) aerosol absorbs sunlight that might have otherwise been reflected to space and changes the radiative heating of the atmosphere and surface. These effects may alter the dynamical and hydrological processes governing cloud formation. A new, microphysical, effect of BC on climate is identified here, in which solar heating within BC-containing cloud condensation nuclei (CCN) slows or prevents the activation of these CCN into cloud drops. Solar-heated BC-containing droplets are elevated in temperature by fractions of a degree above the ambient, thus raising the droplet vapor pressure and inhibiting activation of the most absorptive CCN. This paper develops the theory describing the alteration of the Köhler curve (i.e., the equilibrium vapor pressure over a droplet as a function of water uptake) as a function of CCN size and BC fraction. The effect is most significant in those CCN that contain volumes of BC larger than a 500 nm diameter sphere. For an aerosol population with 10% BC mass fraction per particle, solar heating can cause a 10% reduction in the CCN concentration at 0.01% critical supersaturation. On the other hand, the effect of heating by BC absorption on CCN activation above ∼0.1% critical supersaturation is negligible.

KW - Black carbon

KW - CCN

KW - Cloud condensation nuclei

KW - Droplet thermodynamics

KW - Kohler theory

KW - Soot

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