Annual cycle of hygroscopic properties and mixing state of the suburban aerosol in Athens, Greece
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Published:2023-01-06
Issue:1
Volume:23
Page:235-249
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Spitieri Christina, Gini Maria, Gysel-Beer MartinORCID, Eleftheriadis KonstantinosORCID
Abstract
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 analyser (HTDMA). Four dry particle sizes
(D0) were selected to be analysed 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,
1.13 and 1.22, respectively. The hygroscopic growth spectra were divided
into two distinct hygroscopic ranges: a non- and/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/urban 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, either with a distinct bimodal structure or with
partly overlapping modes. Cluster analysis on the hourly dry number size
distributions was performed to identify the link between aerosol
hygroscopicity and aerosol emission sources and formation processes. The
size distributions were classified into five groups, with the “mixed urban
and regional background” aerosol (67 %) and the “fresh traffic-related
particles” from the neighbourhood urban area (15 %) accounting for more
than 80 % of the results. The hygroscopic properties for 50 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 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).
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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