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| Titel |
Annual measurement of size resolved particle fluxes over an urban area |
| VerfasserIn |
Malte Julian Deventer, Frank Griessbaum, Otto Klemm |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078931
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| Zusammenfassung |
| Urban areas exhibit a multitude of well-known particle sources. Therefore, most flux studies
over bigger cities detected almost exclusively upward fluxes or aerosol particles. In most of
these studies, the total particle number concentration was measured for a broad size range,
e.g. PM2.5or PM10. However, source apportionment and analytical studies suggest
that particles within such wide size ranges may vary in their origin, longevity, and
chemical composition. The scope of this study is to directly quantify turbulent
exchange of atmospheric aerosol particles (AAP) of 16 different size classes. Aerosol
dynamics are analyzed in combination with the exchange fluxes of sensible heat, water
vapor, and carbon dioxide. Furthermore, annual time series are analyzed for seasonal
trends.
We employed the Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) and a Passive
Cavity Aerosol Spectrometer Probe (PCASP-X2), both manufactured by Droplet
Measurement Technologies, Boulder, Colorado (USA). This setup covers the aerosol particle
size range between 0.6 μm and 10 μm diameters in up to 140 size bins. In order to reach
acceptable counting statistics and to minimize random flux errors, we combine the initial 140
bins into 16 wider size bins. Nevertheless, the measurement yields a considerable
improvement in terms of sizing information in comparison to that in previous studies. The
measurements are conducted at a 65 m high telecommunication tower in the city of
Münster (population ~ 275.000), NW Germany, throughout the year of 2012 and
beyond.
The results confirm the hypothesis that urban areas can act both as sources and sinks for
AAP at the same time. We regularly observe bi-directional fluxes as a function of particle
size. While smaller particles typically exhibit (upward) emission fluxes, the larger particles
show deposition (downward fluxes). The tipping point (TP) between mostly up- and
downward transported particles lies in the accumulation mode at about 180 nm diameter.
Large numbers of particles smaller than the TP are emitted out of the city, leading to
positive daily number fluxes of 2 – 4.8 -
108# m-2 d-1. Comparatively few particles
bigger than the TP deposit into the city, often causing a negative daily mass flux of
-0.1 – -0.7 μg m-2 d-1. Number fluxes show typical daily patterns, which are
correlated to traffic activity and turbulence characteristics. Spring- and summer
fluxes are up to two times as high as the winter fluxes, which can be attributed
to the considerably less developed turbulence within the boundary layer during
the cold season. Accordingly, particle concentrations are nearly doubled during
winter.
The presentation will further deepen the size differentiated analysis of particle fluxes and
concentrations. |
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