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| Titel |
Cloud glaciation by mineral dust, soot and biological particles |
| VerfasserIn |
Corinna Hoose, Jón Egill Kristjánsson, Susannah Burrows, Jen-Ping Chen, Anupam Hazra |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033454
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| Zusammenfassung |
| An ice nucleation parameterization based on classical nucleation theory, with aerosol-specific
parameters derived from experiments, has been implemented into the global climate model
CAM-Oslo. The parameterization treats immersion, contact and deposition nucleation by
mineral dust, soot, bacteria, fungal spores and pollen in mixed-phase clouds. The role of
primary biological aerosol particles (PBAP) as heterogeneous ice nuclei is investigated for
the first time with a global model. Emission parameterizations for bacteria, fungal spores
and pollen based on recent literature are introduced. The simulated PBAP number
concentrations are compared to data from various locations. Taking into account the
uncertainties in measurement methods and the possibly limited representativeness of
short-term, locally influenced observations for a larger region and longer time span, the
agreement between measurements and observations is overall satisfactory. While
the simulated bacteria and fungal spore concentrations are of the correct order of
magnitude, the model tends to underestimate total PBAP number. This likely indicates
that either pollen or other (possibly submicron) PBAP that are not considered here
contribute significantly to the total PBAP number at the measurement locations.
Immersion freezing by mineral dust is found to be the dominating ice formation
process, followed by immersion and contact freezing by soot. The simulated biological
aerosol contribution to global atmospheric ice formation is marginal, even with high
estimates on their ice nucleation activity, because the number concentration of ice
nucleation active biological particles in the atmosphere is low compared to other ice
nucleating aerosols. The ice nuclei concentrations in the model agree well with
in-situ continuous flow diffusion chamber measurements, and reflect a correlation
between ice nuclei at temperatures below -20-C and coarse-mode aerosol particles.
Their simulated composition (82% mineral dust, 18% soot and 10-5% biological
particles) lies in the range of observed ice nuclei and ice crystal residue compositions.
Even with high estimates for bacteria emissions and unrealistically high PBAP
freezing efficiency assumptions, it is not higher than 1%. Observed biological ice
nuclei concentrations in snow are reasonably well captured by the model. This
implies that ’bioprecipitation’ processes (snow and rain initiated by PBAP) are of
minor importance on the global scale. The observed high biological IN/ice crystal
residue concentrations in specific cases and events are possibly linked to variations
in PBAP concentrations and/or ice nucleation efficiencies far above the average. |
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