LONG-TERM STUDY OF URBAN NEW PARTICLE FORMATION (NPF) EVENTS AND
THEIR IMPACT ON CLOUD CONDENSATION NUCLEI (CCN)
C.DAMETO DE ESPANA1, A. WONASCHÜTZ 1 , G. STEINER 1,2, B. ROSATI1, A. DEMATTIO1, J.
BURKART3, R. WAGNER4, H. SCHUH1 AND R. HITZENBERGER1
1
University of Vienna, Faculty of Physics, Aerosol Physics and Environmental Physics,
Boltzmanngasse 5, A-1090 Vienna, Austria.
2
University of Innsbruck, Institute for Ion Physics and Applied Physics,
Technikerstraße 25, A-6020 Innsbruck.
3
Vienna University of Technology, Institute of Materials Chemistry,
Getreidemarkt 9/165, A-1060 Vienna, Austria
4
University of Helsinki, Department of Physics,
P.O. Box 64, FI-00014 University of Helsinki, Finland
Keywords: New Particle Formation, Cloud Condensation Nuclei, Long-term study, Urban Aerosol.
INTRODUCTION
Observations and model studies (e.g. Kerminen et al., 2012) have demonstrated that New Particle
Formation (NPF) events can be an important source of cloud condensation nuclei (CCN) in the
atmosphere. However, the observations often only consider particle growth to a certain threshold in size
distribution measurements. Just few studies (e.g. Asmi et al., 2011, Wiedensohler et al., 2009), have linked
observed NPF and growth events directly to increases in measured CCN concentrations. Clearly, there is a
lack of continuous long-term parallel measurements of CCN concentrations and of NPF events
particularly in urban aerosols. Here, we present a 19-month CCN study embedded in a long term study of
NPF events in the urban background
METHODS
Atmospheric aerosol measurements are performed in the rooftop laboratory of the Faculty of Physics in
the urban background of Vienna. Continuous size distribution measurements in the range of 10 – 600 nm
have been conducted from September 2007 until December 2008 and from March 2012 until December
2016 with a Vienna type Differential Mobility Particle Sizer (DMPS) and an SMPS 3082 (TSI, Inc.)
Simultaneous CCN concentration measurements were carried out from June 2014 to December 2015 with
the Vienna Cloud Condensation Nuclei Counter (CCNC) (Dusek et al., 2006) operated at a nominal
supersaturation of 0.5%. Total particle number concentrations were tracked to determine the activation
ratio. Black carbon (BC) concentrations were measured with a Multi Angle Absorption Photometer
(MAAP, Thermo Scientific) and used as tracer for traffic emissions. Hourly meteorological data were
provided by the Central Institute for Meteorology and Geodynamics (ZAMG) situated 1 km north
(Station: Hohe Warte) of the laboratory. Recorded size distributions were analysed in 24-hour sets
spanning from midnight to midnight. The criteria by Dal Maso et al., 2005 were used to classify size
distributions into event days, non-event days and undefined days.
RESULTS
Most of the NPF events happened during spring and summer. For example, in 2014 and 2015, events
were observed on 69 (i.e. 13%) of the 539 measurement days, which is similar to the results presented in
the study by Wonaschütz et al. (2015) and lower than in other central European long-term urban studies
(Skrabalova et al., 2015). The results of the monthly size distribution classification for 2014 and 2015 are
shown in Figure 1.
Figure 1. Monthly size distribution classification for 2014 and 2015
During the simultaneous CCN measurements in 2014 and 2015, 69 events were observed, and in 38
events, CCN concentration data were sampled to evaluate the impact of NPF on CCN concentrations. In
the urban background, NPF events and the continuing growth of the newly-formed particles are sometimes
superposed by local pollution plumes. Traffic emissions could additionally increase the concentration of
particles during a NPF event and CCN concentrations can vary due to weather conditions.
In order to study the impact of NPF on CCN concentrations, CCN concentrations before and after an event
were compared when no changes in local emissions were observed and weather conditions before and
after the event were similar. Figure 2 shows a contour plot of particle size distribution and a time series of
the CCN concentration, observed on an event day where CCN concentrations before and after the event
were compared. In 17 occasions, increases in CCN concentrations after event were observed.
Figure 2. CCN concentration during a NPF
CONCLUSIONS
From the 38 evaluated NPF events with CCN data, BC concentrations and weather conditions were
unchanged before and after the events in 17 occasions. In these cases, CCN concentrations after and
before the event could be compared. Changes in CCN concentrations could, however, have occurred also
by changes in boundary layer height or air mass. To take into account these influences, selection criteria
were developed (Dameto de Espana et al., 2017). Applying these criteria, NPF was found to be a source of
CCN in 14 of the 17 events in the urban background of Vienna.
ACKNOWLEDGEMENTS
This study was supported by the Austrian Science Fund (FWF; grant P19515-N20). The authors thank the
Austrian Central Institute for Meteorology and Geodynamics (ZAMG) for providing meteorological data
and the Viennese Environmental Department (MA 22) for air quality monitoring network data.
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