Characterization of aerosol properties at Cyprus, focusing on cloud condensation nuclei and ice-nucleating particles

As part of the A-LIFE (Absorbing aerosol layers in a changing climate: aging, LIFEtime and dynamics) campaign, ground-based measurements were carried out in Paphos, Cyprus, to characterize the abundance, properties, and sources of aerosol particles in general and cloud condensation nuclei (CCN) and ice-nucleating particles (INP) in particular. New particle formation (NPF) events with subsequent growth of the particles into the CCN size range were observed. Aitken mode particles featured κ values of 0.21 to 0.29, indicating the presence of organic materials. Accumulation mode particles featured a higher hygroscopicity parameter, with a median κ value of 0.57, suggesting the presence of sulfate and maybe sea salt particles mixed with organic carbon. A clear downward trend of κ with increasing supersaturation and decreasing d crit was found. Super-micron particles originated mainly from sea-spray aerosol (SSA) and partly from mineral dust. INP concentrations ( N INP ) were measured in the temperature range from −6.5 to −26.5 ∘ C, using two freezing array-type instruments. N INP at a particular temperature span around 1 order of magnitude below −20 ∘ C and about 2 orders of magnitude at warmer temperatures (T>-18 ∘ C). Few samples showed elevated concentrations at temperatures >-15 ∘ C, which suggests a significant contribution of biological particles to the INP population, which possibly could originate from Cyprus. Both measured temperature spectra and N INP probability density functions (PDFs) indicate that the observed INP (ice active in the temperature range between −15 and −20 ∘ C) mainly originate from long-range transport. There was no correlation between N INP and particle number concentration in the size range >500 nm ( N >500 nm ). Parameterizations based on N >500 nm were found to overestimate N INP by about 1 to 2 orders of magnitude. There was also no correlation between N INP and particle surface area concentration. The ice active surface site density ( n s ) for the polluted aerosol encountered in the eastern Mediterranean in this study is about 1 to 3 orders of magnitude lower than the n s found for dust aerosol particles in previous studies. This suggests that observed N INP PDFs such as those derived here could be a better choice for modeling N INP if the aerosol particle composition is unknown or uncertain.