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Identifier 000456168
Title Atmospheric New Particle Formation over the Eastern Mediterranean; its impact on Cloud Condensation Nuclei and Droplet number
Alternative Title Φαινόμενα σχηματισμού νέων σωματιδίων στην Ανατολική Μεσόγειο· η επίδρασή τους στους πυρήνες συμπύκνωσης νεφών και τα νεφοσταγονίδια
Author Καλκαβούρας, Παναγιώτης Ν.
Thesis advisor Μιχαλόπουλος, Νικόλαος
Reviewer Νένες, Αθανάσιος
Τόμπρου-Τζέλλα, Μαρία
Κανακίδου, Μαρία
Περγαντής, Σπύρος
Hussein, Tareq
Μπουγιατιώτη, Αικατερίνη
Abstract New particle formation (NPF) is an atmospheric phenomenon, observed in many environments globally, that contributes to a major fraction (50%) of the global aerosol number budget thereby affecting climate, air quality, and human health. In this thesis, we examine the drivers behind NPF in two different environments in the Eastern Mediterranean, analyze the regional character of such events, and their impact on cloud condensation nuclei (CCN) and cloud droplet number concentrations (CDNC or 𝑁𝑑). Additionally, we analyse particle number size distribution (PNSD) data for characterization and source apportionment purposes at an urban background site in central Athens. To investigate the exact mechanism triggering NPF, concurrent PNSD measurements spanning a 2-year period were conducted in the urban environment of Athens, and at the regional background site of Finokalia, Crete, situated 350 km south. The analysis revealed NPF events with a relative frequency of 20% at both sites, with all events occurring during midday thus highlighting the crucial role of photochemistry. We observed simultaneous NPF events at both sites on 5% of the total examined days. The simultaneous events were all related to air masses stemming from the Northern sector, thus advocating the regional character of an event in the extended geographical area under study. The intensive regional NPF events tend to occur concomitantly at both sites under low condensation sink conditions, elevated SO2, low relative humidity, and low dynamic (i.e. formation and growth rates) parameters. Utilizing additional PNSD measurements from an urban background site in the Middle East (Amman), we also investigated the regional mechanism of NPF in the Eastern Mediterranean and Middle East, sites that are separated by 1,300 km. We discovered that NPF events may spread to even greater distances, as we detected simultaneous NPF event days between all three sites. All events were associated with the Northen air masses that circulated over the Eastern Mediterranean, becoming enriched in sulfur-rich precursors, which further favors the NPF and growth process. To evaluate the impact of NPF on CCN and CDNC, we analysed 7 years of PNSD and aerosol chemical composition data from the remote background site at Finokalia. A new method was introduced to estimate the onset and time duration of the influence on CCN levels of 162 observed NPF episodes. We found that NPF increases CCN number concentrations from 29% to 77% after its onset, and during the afternoon. Using a droplet parameterization, we further quantified the effect of NPF on CDNC at typical updraft velocities (𝑤=0.3 m s-1 ) in clouds. We showed that NPF increases the CDNC by 13%, and that the supersaturations that develop are extremely low (0.03% to 0.27%). The effect of low supersaturations levels, due to water vapor competition, helps to explain the relationship between CCN and CDNC. The competition for water vapor increases when CCN are appeared, and simultaneously suppresses the cloud formation, as the ambient maximum supersaturation (𝑠𝑚𝑎𝑥) is decreased; this feature restricts the influence of NPF on CDNC, making its contribution on CDNC detectable mainly during the night. In the current urban atmosphere NPF is considered as one of the major sources of ultrafine particles (UFPs; diameter 100 nm), which cause serious adverse effects to human health. Applying statistical tools on PNSD measurements (k-means clustering and Positive Matrix Factorization; PMF), we examined the sources and temporal variability of UFPs for two typical seasonal periods (warm vs. cold), and also during a winter lockdown period. Performing k-means clustering analysis, we found 5 common clusters linked to i) high- and ii) low-traffic, iii) NPF, iv) urban background aerosol and v) regional aerosol for all studied periods, while there were two additional clusters related to nighttime anthropogenic activity. In the case of the warm period this cluster is associated with leisure activities, while during the cold and lockdown periods the respective nighttime cluster is linked with biomass burning. A PMF receptor model identified and quantified major sources contributing to particle number concentrations (PNC), which were also related to those extracted by the cluster analysis. In the warm period, the mean PNC contribution of local sources was comparable (40% vs. 60%) to that of secondary processes (regional transport, area background and nucleation). However, the local contribution was significantly enhanced (13% vs. 87%) in the cold period due to residential wood burning.
Language English
Subject CCN
Cloud droplets
NPF
Regional
Source apportionment
UFP, Ultrafine Particles
Καταμερισμός πηγών υπερλεπτών σωματιδίων
Νανοσωματίδια
Issue date 2023-06-16
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/a/5/0/metadata-dlib-1686223021-754853-13076.tkl Bookmark and Share
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