A New particle formation at Po-Valley during PEGASOS campaign

A field campaign was conducted at the polluted rural site, San Pietro Capofiume (SPC) measurement station (44°39? N, 11°37? E; 11 m a.s.l) in the Po Valley, Italy from June 9th to July 10 th 2012 in the frame of the joint Supersito project and the PEGASOS FP7-project. The SPC campaign 2012 data set is unique in the sense that during this campaign a large number of new particle formation (NPF) events were observed. From a total of 32 measurement days 28 days (87.5%) were NPF days. Interestingly, the NPF days showed large differences in terms of particle formation rates J3 (rate of appearance of new particles > 3 nm in cm-3s-1). While growth rates seem to be consistent with earlier study, the formation rates show significant differences. Therefore, three different groups of NPF days were indentified based on the observed formation rates: First group includes days with high formation rates (J 3 cm-3s-1) i.e. values of J3 were between 6 and 14 cm-3s-1; second group includes NPF days with intermediate values of J3 (4-6 cm-3s-1) and the third group includes the NPF days with low rates of J3<4 cm-3s-1. This variability between the NPF days gives us a good opportunity to study the driving factors of NPF at the SPC site. © 2013 AIP Publishing LLC.