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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 7 | Copyright
Atmos. Chem. Phys., 18, 4831-4842, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Apr 2018

Research article | 10 Apr 2018

On the functional form of particle number size distributions: influence of particle source and meteorological variables

Katia Cugerone1, Carlo De Michele1, Antonio Ghezzi1, Vorne Gianelle2, and Stefania Gilardoni3 Katia Cugerone et al.
  • 1Politecnico di Milano, Department of Civil and Environmental Engineering, Milan, Italy
  • 2Regional Agency for Environmental Protection Lombardia, Milan, Italy
  • 3National Research Council, Institute of Atmospheric Science and Climate, Bologna, Italy

Abstract. Particle number size distributions (PNSDs) have been collected periodically in the urban area of Milan, Italy, during 2011 and 2012 in winter and summer months. Moreover, comparable PNSD measurements were carried out in the rural mountain site of Oga–San Colombano (2250ma.s.l.), Italy, during February 2005 and August 2011. The aerosol data have been measured through the use of optical particle counters in the size range 0.3–25µm, with a time resolution of 1 min. The comparison of the PNSDs collected in the two sites has been done in terms of total number concentration, showing higher numbers in Milan (often exceeding 103cm−3 in winter season) compared to Oga–San Colombano (not greater than 2×102cm−3), as expected. The skewness–kurtosis plane has been used in order to provide a synoptic view, and select the best distribution family describing the empirical PNSD pattern. The four-parameter Johnson system-bounded distribution (called Johnson SB or JSB) has been tested for this aim, due to its great flexibility and ability to assume different shapes. The PNSD pattern has been found to be generally invariant under site and season changes. Nevertheless, several PNSDs belonging to the Milan winter season (generally more than 30%) clearly deviate from the standard empirical pattern. The seasonal increase in the concentration of primary aerosols due to combustion processes in winter and the influence of weather variables throughout the year, such as precipitation and wind speed, could be considered plausible explanations of PNSD dynamics.

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The aerosol particle number size distributions (PNSDs) measured in one urban background site (Milan) and in one rural mountainous site (Oga San Colombano) have been studied and compared. Detailed statistical analyses have shown that a common empirical PNSD pattern exists, except for the urban winter data. In order to explain this phenomenon, we analysed the aerosol dynamics by considering the influence of primary aerosol components and the interaction with precipitation and high wind speed.
The aerosol particle number size distributions (PNSDs) measured in one urban background site...