Abstract
Abstract. 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 conclusively linked to NPF events in the atmosphere. 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 always 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 (combined dataset of 85 years from rural and urban backgrounds as well as roadside sites) in Europe. At most sites, a clear positive relation with the frequency of NPF events is found between the solar radiation intensity (up to R2=0.98), temperature (up to R2=0.98), and atmospheric pressure (up to R2=0.97), while relative humidity (RH) presents a negative relation (up to R2=0.95) with NPF event frequency, though exceptions were found among the sites for all the variables studied. Wind speed presents a less consistent relationship, which appears to be heavily affected by local conditions. While some meteorological variables (such as the solar radiation intensity and RH) 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 at higher average 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 relationship with NPF event frequency, though areas with higher average concentrations of SO2 had higher NPF event frequency. Particulate organic carbon (OC), volatile organic compounds (VOCs), and particulate-phase sulfate 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 frequency is reduced.
Highlights
New particle formation (NPF) events are an important source of particles in the atmosphere (Merikanto et al, 2009; Spracklen et al, 2010)
In this study NPF events are generally observed as particles grow from a smaller size to 30 nm or larger
A total of 1952 NPF events with consequent growth of newly formed particles were extracted, and with the use of binned linear regression, the relationship between three variables associated with NPF events (NPF event frequency, formation, and growth rate) and meteorological conditions as well as atmospheric composition was studied
Summary
New particle formation (NPF) events are an important source of particles in the atmosphere (Merikanto et al, 2009; Spracklen et al, 2010). The many studies conducted have included many different types of locations (urban, traffic, regional background) around the world, and differences were found in both the seasonality and intensity of NPF events. The negative effect of increased temperature upon the stability of molecular clusters should not be overlooked (Kürten et al, 2018; Zhang et al, 2012) The former factor appears frequently be dominant, as higher growth rates are found in most cases in the local summer (Nieminen et al, 2018), the actual importance of VOCs in the occurrence of NPF events is still not fully elucidated, with oxidation mechanisms still under intense research (Tröstl et al, 2016; Wang et al, 2020). Extreme values of those variables may be favourable for the occurrence of NPF events, as they are associated with increased mixing in the atmosphere but at the same time suppress nucleation due to increased dilution of precursors (Brines et al, 2015; Rimnácová et al, 2011; Shen et al, 2018; Siakavaras et al, 2016) or favour it due to a reduced condensation sink (CS)
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