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| Titel |
Atmospheric new particle formation and the potential role of organic peroxides |
| VerfasserIn |
Katrin Trawny, Boris Bonn, Stefan Jacobi |
| 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 |
250041319
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| Zusammenfassung |
| New particle formation in the atmosphere belongs to the currently most discussed
aspects of atmospheric aerosols with significant implications for cloud formation and
microphysics, once these particles have grown beyond about 50Â nm in particle diameter. If
these particles act as cloud condensation or ice nuclei they can affect the radiation
budget at the Earths surface and cause climate couplings important to understand
when aiming to predict climate change scenarios. One aspect widely discussed is
the potential contribution of organic trace gases from anthropogenic and biogenic
sources. In this study we analysed datasets from a Central European measurement
station in Germany in a spruce forest approximately 800Â m above sea level and a
distance of about 20Â km to Frankfurt (southeast). Continuous particle size distribution
measurements were classified in nucleation-event or not and unidentified and intercompared
to meteorological and basic trace gas observations. Additionally meteorological
backtrajektories calculated by the German Weather Service for the station every
12Â hours have been considered. These led to the following conclusions: Nucleation was
most likely if (A) the air has not get significantly into touch with the surface within
the last days, or if (B) at least human impact was minor and the air faced forest
surfaces mainly (northwest). As observed already in Hyytiälä (Finland) nucleation
appeared, when the relative humidity and ambient water vapour mixing ratio were
low, ozone was high and the condensation sink was small. A further important
point was the amount of global radiation measured at the Taunus Observatory (Mt.
Kleiner Feldberg). The higher the radiation, the more likely a nucleation event
and the more intense. Temperature impacted on the intensity of nucleation, i.e. the
higher the temperature the more intense the event, but did not directly affect the
occurrence of an event or not, if a threshold value of ca. -6Â -C was exceeded. This latter
observation indicates a potential role of biogenic volatile organic compounds (VOCs) as
their emission is strongly coupled to temperature. Because of our observations in
the laboratory and beacuse of observed nighttime events, we approximated the
concentration of different radicals, e.g. OH, HO2 and RO2. The values of RO2 and
especially the ones of biogenic (e.g. terpene) origin showed a good correlation
with new particle formation occurrence and seemed to be one essential point of
several to allow new particle formation to occur. This might be an indication of the
important role of the biosphere and its stress effects for the particle formation process.
The seasonality observed for the time period since February 2008 displayed two
maxima in May and August, September with a minimum in June, when the weather
conditions were more humid and is in line with the observations made above. July and
August displayed the higest HO2 concentrations, which will act as a sink for the
organic peroxy radicals. In connection to the supressive effect of water vapour on
terpene induced nucleating molecules (secondary ozonides) this might serve as an
explanation for the commonly observed summer minimum in nucleation events. |
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