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| Titel |
Global atmospheric particle formation from CERN CLOUD measurements |
| VerfasserIn |
Eimear M. Dunne, Hamish Gordon, Kenneth S. Carslaw |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148313
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| Publikation (Nr.) |
 EGU/EGU2017-12556.pdf |
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| Zusammenfassung |
| New particle formation (or nucleation) is acknowledged as a significant source of
climate-relevant aerosol throughout the atmosphere. However, performing atmospherically
relevant nucleation experiments in a laboratory setting is extremely challenging. As a result,
until now, the parameterisations used to represent new particle formation in global aerosol
models were largely based on in-situ observations or theoretical nucleation models, and
usually only represented the binary H2SO4-H2O system.
Several different chemicals can affect particle formation rates, even at extremely
low trace concentrations, which are technically challenging to measure directly.
Nucleation rates also respond to environmental changes in e.g. temperature in a highly
non-linear fashion. The CERN CLOUD experiment was designed to provide the most
controlled and accurate nucleation rate measurements to date, over the full range of free
tropospheric temperatures and down to sulphuric acid concentrations of the order of
105 cm−3. We will present a parameterisation of inorganic nucleation rates for
use in global models, based on these measurements, which includes four separate
nucleation pathways: binary neutral, binary ion-induced, ternary neutral, and ternary
ion-induced.
Both inorganic and organic nucleation parameterisations derived from CLOUD
measurements have been implemented in the GLOMAP global aerosol model. The
parameterisations depend on temperature and on concentrations of sulphuric acid,
ammonia, organic vapours, and ions. One of CLOUD’s main original goals was to
determine the sensitivity of atmospheric aerosol to changes in the nucleation rate
over a solar cycle. We will show that, in a present-day atmosphere, the changes in
climate-relevant aerosol (in the form of cloud-level cloud condensation nuclei) over a solar
cycle are on average about 0.1%, with local changes of less than 1%. In contrast,
anthropogenic changes in ammonia since pre-industrial times were estimated to have a much
greater influence, resulting in a radiative forcing of between -0.62 and -0.66 W
m−2.
Including ternary inorganic pathways in GLOMAP improved the model’s agreement with
free tropospheric observations, especially aircraft measurements. The further inclusion of an
organic parameterisation, which increased nucleation in the summertime boundary layer,
brought our results more in line with observations made at surface stations. We therefore
believe that, while the addition of other nucleation pathways (such as amine-induced
nucleation) will doubtless improve agreement with local in-situ measurements,
this model set-up provides a good representation of the global atmosphere as a
whole.
By presenting this novel parameterisation at EGU, we hope to encourage its uptake
among the aerosol modelling community. |
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