Formation and growth of atmospheric nanoparticles in the eastern Mediterranean: results from long-term measurements and process simulations

Nikos Kalivitis,Maria Kanakidou,Panayiotis Kalkavouras,Hanna E Manninen,Aikaterini Bougiatioti,Stelios Myriokefalitakis,Nikos Daskalakis,Pontus Roldin,Evaggelia Tzitzikalaki,Iasonas Stavroulas,Nikolaos Mihalopoulos,Veli-Matti Kerminen,Giorgos Kouvarakis,Markku Kulmala,Tuukka Petäjä,Michael Boy

doi:10.5194/acp-19-2671-2019

Abstract

Abstract. Atmospheric new particle formation (NPF) is a common phenomenon all over the world. In this study we present the longest time series of NPF records in the eastern Mediterranean region by analyzing 10 years of aerosol number size distribution data obtained with a mobility particle sizer. The measurements were performed at the Finokalia environmental research station on Crete, Greece, during the period June 2008–June 2018. We found that NPF took place on 27 % of the available days, undefined days were 23 % and non-event days 50 %. NPF is more frequent in April and May probably due to the terrestrial biogenic activity and is less frequent in August. Throughout the period under study, nucleation was observed also during the night. Nucleation mode particles had the highest concentration in winter and early spring, mainly because of the minimum sinks, and their average contribution to the total particle number concentration was 8 %. Nucleation mode particle concentrations were low outside periods of active NPF and growth, so there are hardly any other local sources of sub-25 nm particles. Additional atmospheric ion size distribution data simultaneously collected for more than 2 years were also analyzed. Classification of NPF events based on ion spectrometer measurements differed from the corresponding classification based on a mobility spectrometer, possibly indicating a different representation of local and regional NPF events between these two measurement data sets. We used the MALTE-Box model for simulating a case study of NPF in the eastern Mediterranean region. Monoterpenes contributing to NPF can explain a large fraction of the observed NPF events according to our model simulations. However the adjusted parameterization resulting from our sensitivity tests was significantly different from the initial one that had been determined for the boreal environment.

Highlights

Most of the atmospheric aerosol particles, and a substantial fraction of particles able to act as cloud condensation nuclei (CCN), have been estimated to originate from new particle formation (NPF) taking place in the atmosphere (Spracklen et al, 2006; Kerminen et al, 2012; Gordon et al, 2017)
We found that Aitken mode accounted for 50 % and accumulation mode for 42 % of the total particle number concentration, while the nucleation mode accounted only for 8 %
Calculating the median diurnal variability of the nucleation mode, we can see that there is a clear pattern for all seasons of the year (Fig. 2a) with a sudden burst in the number concentration around noon that is most pronounced in winter and least in summer

Summary

Introduction

Most of the atmospheric aerosol particles, and a substantial fraction of particles able to act as cloud condensation nuclei (CCN), have been estimated to originate from new particle formation (NPF) taking place in the atmosphere (Spracklen et al, 2006; Kerminen et al, 2012; Gordon et al, 2017). Based on ion observations, Pikridas et al (2012) showed that NPF is more frequent in winter. By using the same data set from the eastern Mediterranean, Kalivitis et al (2012) reported nighttime enhancements in ion concentrations with a plausible association with NPF, being among the very few locations where such observations have been made. Manninen et al (2010) presented an analysis of a full year of observations of NPF with atmospheric ion spectrometers at various locations across Europe during the EUCAARI project and showed that NPF is less frequent at the eastern Mediterranean site than at other, mostly continental, European sites. Kalivitis et al (2015), for the first time, studied the NPF–CCN link using observations of particle number size distributions, CCN and high-resolution aerosol chemical composition for the eastern Mediterranean atmosphere. Kalkavouras et al (2017) reported that NPF may result in higher CCN number concentrations, but the effect on cloud droplet number is limited by the prevailing meteorology

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Results

Conclusion