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 Gilardoni31Politecnico di Milano, Department of Civil and Environmental Engineering, Milano, Italy 2Regional Agency for Environmental Protection Lombardia, Milano, Italy 3National Research Council, Istitute of Atmospheric Science and Climate, Bologna, Italy
Received: 26 Nov 2016 – Accepted for review: 01 Mar 2017 – Discussion started: 24 Mar 2017
Abstract. Particle number size distributions (PNSDs) have been collected periodically in Milan urban area, 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 (2250 m a.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 0.3–25 µm, mainly belonging to the coarse mode (PMcoarse), with a time resolution of one minute. 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 103 cm−3 in winter season) compared to Oga-San Colombano (not greater than 2 ∙ 102 cm−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 SB (JSB) distribution has been tested for this aim, due to its great flexibility and ability of assuming different shapes. The PNSD pattern has been found to be generally invariant under site and season changes. Nevertheless, several PNSDs belonging to Milan winter season (generally more than 30 %) clearly deviate from the standard empirical pattern. The seasonal increase of the concentration of primary aerosols due to combustion processes in winter and the influence of weather variables, such as precipitation and wind speed, throughout the year, could be considered plausible explanations of PNSD dynamics.
Cugerone, K., De Michele, C., Ghezzi, A., Gianelle, V., and Gilardoni, S.: On the functional form of particle number size distributions:
influence of particle source and meteorological variables, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1054, in review, 2017.