Ground-based measurements on aerosol particles at Paphos, Cyprus, in March-April 2017

Super-micron particles originated mainly from sea spray aerosol (SSA) and partly from mineral dust. INP concentrations (NINP) were measured in the temperature range from −6.5 to −26.5 ℃, using two freezing array type instruments. NINP at a particular temperature span around 1 order of magnitude below −20 ℃, and about 2 orders of magnitude at warmer temperatures (T> −18 ℃).

Few samples showed elevated concentrations at temperatures > −15 ℃, which suggests a significant contribution of biological particles to the INP population, which possibly could originate from Cyprus. Both measured temperature spectra and NINP probability density functions (PDFs) indicate that the observed INP (ice active in the temperature range between −15 and −20 ℃) mainly originate from long-range transport. There was no correlation between NINP and particle number concentration in the size range >500 nm (N>500nm).

Parameterizations based on N>500nm were found to overestimate NINP by about 1 to 2 orders of magnitude. There was also no correlation between NINP and particle surface area concentration. The ice active surface site density (ns) for the polluted aerosol encountered in the eastern Mediterranean in this study is about 1 to 3 orders of magnitude lower than the ns found for dust aerosol particles in previous studies.

This suggests that observed NINP-PDFs as those derived here could be a better choice for modelling NINP if the aerosol particle composition is unknown or uncertain.