Particle number size distribution statistics at City-Centre Urban Background, urban background, and remote stations in Greece during summer

doi:10.1016/j.atmosenv.2019.05.064

Atmospheric Environment

Volume 213, 15 September 2019, Pages 711-726

https://doi.org/10.1016/j.atmosenv.2019.05.064 Get rights and content

Highlights

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Particle number size distribution in the Eastern Mediterranean during the Etesians.
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Derivation of aerosol sources at five stations and comparison to previous studies.
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Distinction between long range transported and locally produced aerosol particles.
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Air mass origin impact on the background particle number concentration.
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Nucleation events during summer are rarely observed (0–9% of calendar days).

Abstract

Particle number size distribution measurements were conducted during the summer of 2012 at City-Centre Urban Background (Patras-C), Urban Background (ICE-HT in Patras, DEM in Athens, EPT in Thessaloniki), and Regional Background stations (FIN in Crete). At the City-Centre Urban Background station, the average number distribution had a geometric mean diameter peak approximately at 60 nm and the highest number concentration, whereas at the Regional Background station and the Urban Background stations it displayed a major peak approximately at 100 nm, with the Regional Background station exhibiting the lowest number concentration. The particle number size distribution at each site was divided into size fractions and, based on their diurnal variation and previous studies, we concluded that the main sources for the City-Centre Urban Background station are traffic and the regional background concentration, for the Urban Background stations fresh traffic, aged traffic, cooking and the regional background concentration, and for the Regional Background station local activities (tourism, cooking) and regional background concentration. The median number concentration that is attributed to regional background concentration for the City-Centre Urban Background, the Urban Background and the Regional Background stations are respectively 13, 29 and 45% of the total number concentration. Nucleation events were identified at DEM station, where the newly formed particles accounted for 4% of the total particle concentration for the measurement period in the size range 10–20 nm, EPT, where they accounted for 12%, and FIN, where they accounted for 1%, respectively. New Particle Formation events contribution during summer to Condensation Cloud Nuclei were therefore insignificant in the Eastern Mediterranean. Modal analysis was performed on the number distributions and the results were classified in clusters. At the City-Centre Urban Background station, the cluster-source that dominated number concentration and frequency is related to fresh and aged traffic emissions, at the Urban Background stations aged traffic emissions, while at the Regional Background station number and frequency were dominated by the regional background concentration. Based on cluster analysis, 18% of the median number distribution was due to long range transport at the City-Centre Urban Background site, 37% at the Urban Background sites, and 59% at the Regional Background site. The Flexible Particle Dispersion Model (FLEXPART) was used in order to acquire geographic origin clusters and we concluded that the Etesian flow increases the median regional background number concentration in the Mediterranean basin by a factor of 2.5–4.

Graphical abstract

Introduction

The atmospheric aerosol is generated by natural and anthropogenic processes and its lifetime ranges from a few hours, for resuspended coarse dust, to several days, for fine primary and secondary aerosol (e.g. black carbon, sulphate) (Eleftheriadis et al., 2006). Atmospheric particles are characterized by marked differences in chemical composition and physical properties. Their composition may be directly influenced by anthropogenic emissions of primary particles, condensation of gaseous precursors of anthropogenic or natural origin, and natural sources such as the sea and erodible soils (Seinfeld and Pandis, 1998).

Atmospheric aerosol particles affect air quality, human health, atmospheric visibility, and the climate (Laden et al., 2006; Eleftheriadis et al., 2014; Stafoggia et al., 2017). To understand these effects, measurements of their size distribution and chemical composition are highly needed.

The climate effects of aerosols with dry diameters larger than 50 nm are divided into two groups. The direct effect represents the ability of the atmospheric particles to absorb and scatter short-wave radiation and thus directly affect the radiation balance. These direct effects depend primarily on the aerosol optical properties and particle size distribution (Bond et al., 2013). The indirect effects rely on the ability of aerosol particles to act as condensation nuclei during cloud formation, affecting both the reflectance and the lifetime of the clouds.

During summer and early autumn (warm period), the circulation over the Eastern Mediterranean is dominated by a persistent northerly flow known as the Etesians (Tyrlis and Lelieveld, 2013). When the Etesians prevail, the advection of air masses is evident over the Eastern Mediterranean, rendering the long range transport as the most important factor for high concentrations of gases and aerosol particles. Airborne measurements performed during an Etesian outbreak (Tombrou et al., 2015) clearly show that neutral to stable atmospheric conditions prevail over the Northern and Central Aegean Sea, with reduced friction velocities and absolute turbulent fluxes (momentum or heat) cumulating the concentrations below the planetary boundary layer and mainly inside the shallow marine atmospheric boundary layer. Unstable conditions are observed only over the South Eastern Aegean Sea, in the vicinity of Crete, resulting in enhanced friction velocities and large positive values of sensible heat flux. In previous studies, the fine aerosol fraction over the Aegean Sea has been related to regional sources of pollution which is enhanced by long-range transport during the Etesian flow. A mixture of anthropogenic (Koçak et al., 2011), biogenic (Im and Kanakidou, 2012), and biomass burning emissions (Bougiatioti et al., 2014) originating mainly from the Balkan area, as well as the central and Eastern Europe (Diapouli et al., 2014), results in enhanced aerosol concentrations in the Southern Aegean Sea.

At the same time, high number concentrations of nucleation-mode particles are observed in the Northern Aegean Sea (Triantafyllou et al., 2016), associated with polluted air masses transported from Istanbul. Kalkavouras et al. (2017) proposed that based on simulations, what contributed to new particle formation (NPF) events was the clean air masses of low preexisting aerosol particles with sufficient H₂SO₄from high altitudes. During the NPF period, the air masses pass over the greater Istanbul area, avoiding mixing with the local emissions. Thereafter, they penetrate at lower levels (due to the Etesian flow structure) over North Western Turkey. During the non-NPF period, the air masses suffered a strong mixing during their longer journey over the Turkish mainland. Without excluding the role of photochemistry in NPF, it was shown by both measurements and simulations that the plume over the Aegean Sea moved fast with rather negligible mixing, especially above the marine atmospheric boundary layer. The fast advection above marine atmospheric boundary layer and the low number of preexisting concentrations inside the plume prevented the subsequent growth of the nucleated particles towards the central Aegean Sea. Although long datasets of particle number concentration data in the Eastern Mediterranean are not available, Asmi et al. (2011) report a mean particle concentration of 1.6×10³ particles per cm³at Finokalia (FIN) regional station during 2008 and 2009.

In this study, we aim to report the particle number concentration in the Eastern Mediterranean during the Etesian flow, in City-Centre Urban Background, Urban Background and Regional Background stations using high time resolution instrumentation. We intend to determine the corresponding aerosol sources and evaluate the relative significance of each source at each station type and compare the Particle Number Size Distribution (NSD) obtained at each site to the corresponding NSD and sources in previous studies. We want to distinguish between long-range transported and locally produced aerosol particles and evaluate the air mass origin impact on the particle number concentration due to long range transport in the Eastern Mediterranean during summer. Also, we would like to evaluate the impact of New Particle Formation (NPF) on to the NSD measured in the Eastern Mediterranean during the Etesians and consequently NPF impact on Condensation Cloud Nuclei concentration (CCN).

Section snippets

Materials and Methods

Simultaneous particle size distribution measurements were performed at five sampling stations in Greece. The measurements were conducted in Patras, Athens, Thessaloniki and Finokalia (Fig. 1), during June and July 2012.

Patras is located at the foothills of a mountain with a height of approximately 2 km, at the Gulf of Patras. It is an urban area with a population of approximately 300,000 inhabitants. Measurements were conducted simultaneously at two stations in Patras.

The City-Centre Urban

Overview of concentration levels and size distributions

Comparisons between measured and modeled concentrations test-img are usually done using the arithmetic means of the relevant quantities. A typical arithmetic mean comparison is of less use for these distributions, as the values of linear means are strongly affected by the outlier values. A way to compare the results would then be the ability of a model to reproduce the measured concentration histograms. In this article we use mostly the percentile values of the number size distributions in

Summary and conclusions

SMPS particle number concentrations at City-Centre Urban Background, Urban Background and Regional Background stations in Greece during the summer of 2012 were investigated. The peak concentration at the City-Centre Urban Background station is approximately at 60 nm, while at the Urban and Regional Background stations is at approximately 100 nm. The highest particle number concentration values were observed at the City-Centre Urban Background station (Patras-C). Also, the median particle number

Declarations of interest

None.

Acknowledgements

This research has been co-funded by the EnTeC FP7 Capacities program (REGPOT-2012-2013-1, FP7 (ID:316173)) and Greek national funds through the Operational Program Education and Lifelong Learning of the National Strategic Reference Framework (NSRF) Research Funding Program: THALES. We also acknowledge support of this work by the project PANhellenic infrastructure for Atmospheric Composition and climatE change (MIS 5021516) which is implemented under the Action Reinforcement of the Research and

References (52)

E. Diapouli et al.
Physicochemical characterization of aged biomass burning aerosol after long-range transport to Greece from large scale wildfires in Russia and surrounding regions, summer 2010
Atmos. Environ.
(2014)
K. Eleftheriadis et al.
Size distribution, composition and origin of the submicron aerosol in the marine boundary layer during the eastern Mediterranean “SUB-AERO” experiment
Atmos. Environ.
(2006)
K. Eleftheriadis et al.
Influence of local and regional sources on the observed spatial and temporal variability of size resolved atmospheric aerosol mass concentrations and water-soluble species in the Athens metropolitan area
Atmos. Environ.
(2014)
M. Koçak et al.
Particulate matter (PM10 ) in Is- tanbul: origin, source areas and potential impact on surrounding regions
Atmos. Environ.
(2011)
M. Kulmala et al.
Formation and growth rates of ultra ne atmospheric particles:a review of observation
J. Aerosol Sci.
(2004)
N. Ma et al.
Estimating the contribution of photochemical particle formation to ultrafine particle number averages in an urban atmosphere
Sci. Total Environ.
(2015)
B. Mølgaard et al.
Evaluation of a statistical forecast model for size-fractionated urban particle number concentrations using data from five European cities
J. Aerosol Sci.
(2013)
M.G. Perrone et al.
Sources and geographic origin of particulate matter in urban areas of the Danube macro-region: the cases of Zagreb (Croatia), Budapest (Hungary) and Sofia (Bulgaria)
Sci. Total Environ.
(2018)
M. Pikridas et al.
Characterization of the origin of fine particulate matter in a medium size urban area in the Mediterranean
Atmos. Environ.
(2013)
X. Querol et al.
African dust contributions to mean ambient PM 10 mass-levels across the Mediterranean Basin
Atmos. Environ.
(2009)

T. Caliński et al.

A dendrite method for cluster analysis

Commun. Stat. Theor. Methods

(1974)

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