The Effect of Meteorological Conditions and Atmospheric Composition in the Occurrence and Development of New Particle Formation (NPF) Events in Europe

Although new particle formation (NPF) events have been studied extensively for some decades, the mechanisms that drive their occurrence and development are yet to be fully elucidated. Laboratory studies have done much to elucidate the molecular processes involved in nucleation, but this knowledge has yet to be linked to NPF events in the atmosphere, except at very clean air sites. There is great difficulty in successful application of the results from laboratory studies to real atmospheric conditions, due to the diversity of atmospheric conditions and observations found, as NPF events occur almost everywhere in the world without following a clearly defined trend of frequency, seasonality, atmospheric conditions or event development. The present study seeks common features in nucleation events by applying a binned linear regression over an extensive dataset from 16 sites of various types (rural and urban backgrounds as well as roadsides) in Europe. A clear positive relation is found between the solar radiation intensity, temperature and atmospheric pressure with the frequency of NPF events, while relative humidity presents a negative relation with NPF event frequency. Wind speed presents a less consistent relationship which appears to be heavily affected by local conditions. While some meteorological variables appear to have a crucial effect on the occurrence and characteristics of NPF events, especially at rural sites, it appears that their role becomes less marked when at higher values. The analysis of chemical composition data presents interesting results. Concentrations of almost all chemical compounds studied (apart from O3) and the Condensation Sink (CS) have a negative relation with NPF event probability, though areas with higher average concentrations of SO2 had higher NPF event probability. Particulate Organic Carbon (OC), Volatile Organic Compounds (VOCs) and particulate phase sulphate consistently had a positive relation with the growth rate of the newly formed particles. As with some meteorological variables, it appears that at increased concentrations of pollutants or the CS, their influence upon NPF probability is reduced.