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

Xianda Gong, Heike Wex, Thomas Müller, Alfred Wiedensohler, Kristina Höhler, Konrad Kandler, Nan Ma, Barbara Dietel, Thea Schiebel, Ottmar Möhler, Frank Stratmann
2019 Atmospheric Chemistry and Physics Discussions  
<p><strong>Abstract.</strong> As part of the A-LIFE (<b>A</b>bsorbing aerosol layers in a changing climate: aging, <b>life</b>time and dynamics) campaign, ground-based measurements were carried out in Paphos, Cyprus, for characterizing 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
more » ... bserved. 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. A clear downward trend of κ with increasing supersaturation and decreasing <i>d</i><sub>crit</sub> was found. Super-micron particles originated mainly from sea spray aerosol (SSA) and partly from mineral dust.</p> <p>INP concentrations (<i>N</i><sub>INP</sub>) were measured in the temperature range from &amp;minus;6.5 to &amp;minus;26.5&amp;thinsp;℃, using two freezing array type instruments. <i>N</i><sub>INP</sub> at a particular temperature span around 1 order of magnitude below &amp;minus;20&amp;thinsp;℃, and about 2 orders of magnitude at warmer temperatures (T&amp;thinsp;>&amp;thinsp;&amp;minus;18&amp;thinsp;℃). Few samples showed elevated concentrations at temperatures >&amp;thinsp;&amp;minus;15&amp;thinsp;℃, which suggests a significant contribution of biological particles to the INP population, which possibly could originate from Cyprus. Both measured temperature spectra and <i>N</i><sub>INP</sub> probability density functions (PDFs) indicate that the observed INP (ice active in the temperature range between &amp;minus;15 and &amp;minus;20&amp;thinsp;℃) mainly originate from long-range transport. There was no correlation between <i>N</i><sub>INP</sub> and particle number concentration in the size range >&amp;thinsp;500&amp;thinsp;nm (<i>N</i><sub>>&amp;thinsp;500&amp;thinsp;nm</sub>). Parameterizations based on <i>N</i><sub>>&amp;thinsp;500&amp;thinsp;nm</sub> were found to overestimate <i>N</i><sub>INP</sub> by about 1 to 2 orders of magnitude. There was also no correlation between <i>N</i><sub>INP</sub> and particle surface area concentration. The ice active surface site density (<i>n</i><sub>s</sub>) for the anthropogenically polluted aerosol encountered in this study is about 1 to 3 orders of magnitude lower than the <i>n</i><sub>s</sub> found for dust aerosol particles in previous studies. This suggests that observed <i>N</i><sub>INP</sub>-PDFs as those derived here could be a better choice for modelling <i>N</i><sub>INP</sub> if the aerosol particle composition is unknown or uncertain.</p>
doi:10.5194/acp-2019-198 fatcat:7e6x7ca4srf4pllcydnz4e5kxe