3.2. Particle Number Distribution (PND)
It is traditional to describe the particle size distribution by
means of the sum of several lognormal distributions (Hussein et al.,
2004; Van Dingenen et al., 2005). Each mode can be defined by
three parameters: median diameter, geometrical standard
deviation and particle concentration. Figure 2 show fitted multimodal
particle size distribution indicating these parameters. The
results reveal that PND is characterized by three modes: mode–1
(nucleation), mode–2 (Aitken), and mode–3 (accumulation). The
geometric mean diameters of mode–1 ranged from 13.8 to 14.8
nm for hot events and between 13.8 and 14.1 nm for cold events.
Mode–2 geometric mean diameters ranged between 28.0–34.2 nm
and 28.7–30.6 nm for hot and cold events, respectively. In addition