03 Mar 2022
03 Mar 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Annual Cycle of Hygroscopic Properties and Mixing State of the Suburban Aerosol in Athens, Greece

Christina Spitieri1, Maria Gini1, Martin Gysel-Beer2, and Kostas Eleftheriadis1 Christina Spitieri et al.
  • 1Environmental Radioactivity Laboratory, Institute of Nuclear and Radiological Science & Technology, Energy & Safety, NCSR Demokritos, 15310 Ag. Paraskevi, Athens, Greece
  • 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Forschungsstrasse 111, Villigen PSI, Switzerland

Abstract. The hygroscopic properties of atmospheric aerosol were investigated at a suburban environment in Athens, Greece, from August 2016 to July 2017. The Growth Factor Distribution Probability Density Function, (GF-PDF), and mixing state were determined with a Hygroscopicity Tandem Differential Mobility Analyzer, (HTDMA). Four dry particle sizes, (D0), were selected to be analyzed in terms of their hygroscopic properties at 90 % relative humidity. The annual mean GFs for D0 = 30, 50, 80, and 250 nm, were found to be equal to 1.28, 1.11, 1.14, and 1.22 respectively. The hygroscopic growth spectra can be divided into two distinct hygroscopic ranges; a non or slightly hygroscopic mode (GF ˂ 1.12) and a moderately hygroscopic mode (GF ˃ 1.12), which are representative of a suburban environment influenced by local/regional emissions and background aerosol. The standard deviation σ of the GF-PDF was employed as a measure of the mixing state of ambient aerosol. The 30 nm particles were mostly internally mixed, whereas larger particles were found to be externally mixed, with either a distinct bimodal structure or with partly overlapping modes. Cluster analysis on the hourly dry number size distributions measured in parallel, provided the link between aerosol hygroscopicity and growth/evaporation dynamics. The size distributions were classified into five groups, with the “mixed, urban and aerosol background” (67 %) and “urban-nocturnal” aerosol (12 %) to account for 79 % of the results. The hygroscopic properties for 50 nm and 80 nm were found to be similar in all cases, indicating particles of similar nature and origin across these sizes. This was also confirmed through the modal analysis of the average number size distributions for each cluster; the 50 nm and 80 nm particles were found to belong to the same Aitken mode in most cases. The 250 nm particles (i.e. accumulation mode) were generally more hygroscopic than Aitken particles, but less hygroscopic than the 30 nm particles (nuclei mode).

Christina Spitieri et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-126', Anonymous Referee #1, 05 Apr 2022
    • AC1: 'Reply on RC1', Christina Spitieri, 14 Jul 2022
  • RC2: 'Comment on acp-2022-126', Anonymous Referee #2, 16 May 2022
    • AC2: 'Reply on RC2', Christina Spitieri, 14 Jul 2022

Christina Spitieri et al.

Christina Spitieri et al.


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Short summary
The manuscript aims at providing insights into the hygroscopic properties and state of mixing of atmospheric aerosol, through 1 year of measurements of key microphysical parameters in the suburbs of the most densely populated cities of Greece, Athens, in the Eastern Mediterranean which is considered as an important climate change hotspot. The results can be used for prediction of CCN and quantification of the influence of ambient RH on light scattering by aerosol particles.