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| Titel |
CAPRAM modelling of the speciation and redox-cycling of iron in deliquescent particles and cloud droplets |
| VerfasserIn |
A. Tilgner, R. Wolke, H. Herrmann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028147
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| Zusammenfassung |
| The most abundant TMI in tropospheric particles is iron which plays a crucial role in aqueous
phase chemistry of fog and cloud droplets. The redox-cycling of iron is responsible for many
chemical interactions such as the HOx/HOy processing. However, still large uncertainties of
TMI chemistry exist and less is known about the TMI speciation in the particulate phase.
To this end, the iron speciation and redox cycling in deliquescent particles and
cloud droplets were investigated in more detail by means of model studies using
the SPectral Aerosol Cloud Chemistry Interaction Model (SPACCIM). The parcel
model SPACCIM includes a complex microphysical and multiphase chemistry
model. In chemistry model, the multiphase mechanism RACM-MIM2ext/CAPRAM
3.0i with about 1100 processes was applied incorporating a detailed description of
the tropospheric multiphase processes. Simulations were carried out for different
environmental conditions using a non-permanent meteorological scenario. The model results
have been analysed including time-resolved source and sinks studies. The model
studies were particularly focused on temporal variations in the of iron speciation and
redox-cycling in the condensed phase including its importance for other important
chemical subsystems such as the multiphase HOx,y and organic chemistry. For this
purpose, sensitivity studies have been performed on the importance of the water
soluble iron content for the aqueous phase oxidation capacity and chemical organic
processing.
The model results have shown characteristic diurnal profiles of the iron speciation in both
deliquescent particles and clouds. Moreover, up to about 20 to 50% of the soluble iron is
shown to be still present as Fe2+ during the night which reflects an efficient nighttime
iron-redox-cycling under polluted environmental conditions. Performed comparisons with
available cloud water measurements and former model calculations revealed reasonable
agreements as well as some differences.
The model results have additionally pointed out considerable differences between the iron
cycling in deliquescent particles and cloud droplets. The model results revealed chemical
differences in the sink and source reactions caused by different pH conditions as well as the
different HO2/O2- budget in the two aqueous environments. Moreover, the model results
implicated the role of deliquescent particles to be a reactive medium for the TMI
redox-cycling which is potentially important for other chemical subsystems. Under urban
conditions, the modelled total daytime fluxes in the deliquescent particles are partly about 2
times larger than in daytime clouds.
Finally, the performed studies regarding the relevance of the water soluble iron content
for tropospheric multiphase processes have pointed out that the oxidation budget is quite
sensitive to changes of this crucial parameter. Accordingly, the sensitivity studies corroborate
the need for an iron-redox-chemistry treatment in higher scale chemistry transport models.
However, the studies have also confirmed the necessity for further experimental work
concerning the iron-organic aqueous photochemical interactions to clarify open scientific
issues and mechanism limitations. |
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