Key characteristics and statistical investigation of new particle formation events at a Mediterranean site

Abstract

New particle formation (NPF) events were investigated at a coastal suburban site (Chania, Greece) in eastern Mediterranean during May 2022–April 2023. The particle number size distribution was measured together with particulate matter (PM₁₀) and gaseous pollutants (NO, NO₂, O₃). 16 NPF events (8 Class I and 8 Class II) were observed with higher occurrence on May (5 events), whereas no NPF event took place on winter months. On the other hand, 15 undefined events were identified with a higher number of events present in February. Increased frequency on warm months was associated with enhanced biogenic and photochemical activity. The average condensation sink, the formation and growth rate for all events was 0.007 s⁻¹, 0.16 cm⁻³ s⁻¹ and 2.60 nmh⁻¹ respectively, without statistically significant differences between Class I and Class II events. The formation and growth rates were higher during the warm period. Nucleation particles (14 nm – 25 nm) preserved no seasonal variations but were significantly increased on periods with NPF activity. NPF activity was enhanced by the presence of condensable sinks that favored nanoparticle formation. Both the growth and the formation rates were positively correlated with solar radiation, temperature and wind speed. Two main factors were identified during NPF events: atmospheric conditions (solar radiation, temperature, wind speed and condensation sinks) and the urban environment (NO). NO₂, O₃ and PM₁₀ were not associated with nucleation particles and NPF activity.