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| Titel |
Simplifying aerosol size distributions modes simultaneously detected at four monitoring sites during SAPUSS |
| VerfasserIn |
M. Brines, M. Dall'Osto, D. C. S. Beddows, R. M. Harrison, X. Querol |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 6 ; Nr. 14, no. 6 (2014-03-25), S.2973-2986 |
| Datensatznummer |
250118522
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| Publikation (Nr.) |
 copernicus.org/acp-14-2973-2014.pdf |
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| Zusammenfassung |
The analysis of aerosol size distributions is a useful tool for
understanding the sources and the processes influencing particle number
concentrations (N) in urban areas. Hence, during the one-month SAPUSS
campaign (Solving Aerosol Problems by Using Synergistic Strategies, EU Marie
Curie Action) in autumn 2010 in Barcelona (Spain), four SMPSs (Scanning
Mobility Particle Sizer) were simultaneously deployed at four monitoring
sites: a road side (RSsite), an urban background site located in the
city (UBsite), an urban background site located in the nearby hills of the
city (Torre Collserola, TCsite) and a regional background site located
about 50 km from the Barcelona urban areas (RBsite). The spatial
distribution of sites allows study of the aerosol temporal variability as
well as the spatial distribution, progressively moving away from urban
aerosol sources. In order to interpret the data sets collected, a k-means
cluster analysis was performed on the combined SMPS data sets. This resulted
in nine clusters describing all aerosol size distributions from the four
sites. In summary there were three main categories (with three clusters in
each category): "Traffic" (Traffic 1, "Tclus_1" – 8%;
Traffic 2, "Tclus_2" – 13%; and Traffic 3,
"Tclus_3" – 9%) "Background Pollution" (Urban
Background 1, "UBclus_1" – 21%; Regional Background 1,
"RBclus_1" – 15%; and Regional Background 2,
"RBclus_2" – 18%) and "Special Cases" (Nucleation,
"NUclus" – 5%; Regional Nitrate, "NITclus" – 6%; and
Mix, "MIXclus" – 5%). As expected, the frequency of traffic clusters
(Tclus_1–3) followed the order RSsite, UBsite,
TCsite, and RBsite. These showed typical traffic modes mainly
distributed at 20–40 nm. The urban background sites (UBsite and
TCsite) reflected also as expected urban background number
concentrations (average values, N = 1.0 × 104 cm−3
and N = 5.5 × 103 cm−3, respectively, relative to
1.3 × 104 cm−3 seen at RSsite). The cluster
describing the urban background pollution (UBclus_1)
could be used to monitor the sea breeze circulation towards the regional
background study area. Overall, the RBsite was mainly characterised by
two different regional background aerosol size distributions: whilst both
exhibited low N (2.7 × 103 for RBclus_1
and 2.2 × 103 cm−3 for RBclus_2),
RBclus_1 had average PM10 concentrations higher
than RBclus_2 (27 vs. 23 μg m−3). As regards
the minor aerosol size distribution clusters, the "Nucleation" cluster was
observed during daytime, whilst the "Regional Nitrate" was mainly seen at
night. The ninth cluster ("Mix") was the least well defined and likely
composed of a number of aerosol sources.
When correlating averaged values of N, NO2 and PM (particulate mass)
for each k-means cluster, a linear correlation between N and NO2 with
values progressively increasing from the regional site RBsite to the
road site RSsite was found. This points to vehicular traffic as the
main source of both N and NO2. By contrast, such an association does
not exist for the case of the nucleation cluster, where the highest N is
found with low NO2 and PM.
Finally, the clustering technique allowed study of the impact of
meteorological parameters on the traffic N emissions. This study confirms
the shrinking of freshly emitted particles (by about 20% within 1 km in
less than 10 min; Dall'Osto et al., 2011a) as particles
are transported from the traffic hot spots towards urban background
environments. Additionally, for a given well-defined aerosol size
distribution (Tclus_2) associated with primary aerosol
emissions from road traffic we found that N5–15 nm concentrations can
vary up to a factor of eight.
Within our measurement range of SMPSs (N15–228 nm) and Condensation
Particle Counters (CPCs, N>5 nm), we found that ultrafine particles
within the range 5–15 nm in urban areas are the most dynamic, being a
complex ensemble of primary evaporating traffic particles, traffic tailpipe
new particle formation and non-traffic new particle formation. |
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