Nucleation Events in Melpitz, Germany, and Po Valley, Italy: Similarities and Differences

This study has been designed to investigate the factors that influence the occurrence of new particle formation events (particles >3 nm) in two anthropogenically influenced boundary layer regimes in Central Europe (Melpitz, Eastern Germany) and Southern Europe (San Pietro Capofiume “SPC” in the Po Valley, Italy). In particular, we study the similarities and differences of factors driving nucleation events at these two locations. The analysis encompasses three years of data at each observation site, between July 2003 and June 2006. Particle size distribution measurements were carried out using twin DMPS systems (Differential Mobility Particle Sizers) at each site, with particle size ranges of 3–800 nm, and 3–600 nm at Melpitz and SPC, respectively. In addition to particle size measurements, several gas and meteorological parameters are being measured for stations, including SO2, NO, NO2, NOx, O3, temperature, relative humidity, wind direction, wind speed, global radiation, precipitation, and atmospheric pressure. We utilized these parameters in our analysis of particle formation and growth processes. Our preliminarily results show that for Melpitz station, it is possible to separate between nucleation days and nonnucleation days by using just two variables (a product of radiation and sulphuric dioxide – its increase indicates increase of sulphuric acid concentration – and condensation sink“CS”). This result for Melpitz indicates that low enough CS value is needed together with high enough sulphuric acid production to drive nucleation and vice verse for nonnucleation days. For SPC station the same criterion could not separate nucleation days and nonnucleation days as efficiently as for Melpitz, and an overlap region between nucleation and nonnucleation days remained. Interestingly, however, the nonnucleation days in Po Valley are bound by the same criterion as in Melpitz, and it is the nucleation days that cause the Po Valley overlap.