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Abstract: A significant fraction of atmospheric particles that serve as cloud condensation nuclei (CCN) are thought to originate from the condensational growth of new particle formation (NPF) from the gas phase. Here, 7 years of continuous aerosol and meteorological measurements (June 2008 to May 2015) at a remote background site of the eastern Mediterranean were recorded and analyzed to assess the impact of NPF (of 162 episodes identified) on CCN and cloud droplet number concentration (CDNC) formation in the region. A new metric is introduced to quantitatively determine the initiation and duration of the influence of NPF on the CCN spectrum. NPF days were found to increase CCN concentrations (from 0.10 % to 1.00 % supersaturation) between 29 % and 77 %. Enhanced CCN concentrations from NPF are mostly observed, as expected, under low preexisting particle concentrations and occur in the afternoon, relatively later in the winter and autumn than in the summer. Potential impacts of NPF on cloud formation were quantified by introducing the observed aerosol size distributions and chemical composition into an established cloud droplet parameterization. We find that the supersaturations that develop are very low (ranging between 0.03 % and 0.27 %) for typical boundary layer dynamics (σw ∼0.3 m s−1) and NPF is found to enhance CDNC by a modest 13 %. This considerable contrast between CCN and CDNC response is in part from the different supersaturation levels considered, but also because supersaturation drops from increasing CCN because of water vapor competition effects during the process of droplet formation. The low cloud supersaturation further delays the appearance of NPF impacts on CDNC to clouds formed in the late evening and nighttime – which has important implications for the extent and types of indirect effects induced by NPF events. An analysis based on CCN concentrations using prescribed supersaturation can provide very different, even misleading, conclusions and should therefore be avoided. The proposed approach here offers a simple, yet highly effective way for a more realistic impact assessment of NPF events on cloud formation.
Keywords: regional NPF, CCN, cloud droplets, Eastern Mediterranean, regional background
Published in RUNG: 13.05.2024; Views: 98; Downloads: 2
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Abstract: Atmospheric new particle formation (NPF) is an important source of submicron particles. In remote background environments where local sources are scarce such processes may impact significantly on climate-relevant parameters. On the other hand, in urban environments, newly-formed particles are adding up to submicron particles emitted from primary sources. As the exact mechanism which triggers NPF still remains elusive, so are the circumstances for simultaneous occurrence of such events in two different environments (urban vs. regional background). In this study, concurrent number size distribution measurements were conducted in the urban environment of Athens and at the regional background site of Finokalia, Crete, located 340 km away and spanning a 2-year period. It occurred that the relative frequency of NPF was similar at both sites (around 20%), with a higher frequency during spring and autumn at the urban site, while at the background site most events took place in August and December, during the studied period. There were 35 event days when NPF took place at both sites simultaneously, all associated with air masses originating from the Northern sector, indicating the presence of regional events in the extended geographical area and characterized by low condensation sink (CS). By comparing the common with the non-common class I NPF episodes, we conclude that the conditions applying when regional NPF events with growth are observed in the same day at the surface level of both areas, are: (i) lower CS, (ii) higher SO2 concentrations, (iii) lower RH, and finally (iv) lower formation and growth rates than those observed during the site-specific and more rapidly evolving NPF events.
Keywords: NPF, Athens, Eastern Mediterranean, particle number concentrations, size distributions, concurrent regional events
Published in RUNG: 10.05.2024; Views: 125; Downloads: 0
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Abstract: Atmospheric new particle formation (NPF) events taking place over large distances between locations, featuring similar characteristics, have been the focus of studies during the last decade. The exact mechanism which triggers NPF still remains indefinable, so are the circumstances under which simultaneous occurrence of such events take place in different environments, let alone in environments which are parted by over 1200 km. In this study, concurrent number size distribution measurements were conducted in the urban environments of Athens (Greece) and Amman (Jordan) as well as the regional background site of Finokalia, Crete, all located within a distance of almost 1300 km for a 6-month period (February–July 2017). During the study period Athens and Finokalia had similar occurrence of NPF (around 20%), while the occurrence in Amman was double. When focusing on the dynamic characteristics at each site, it occurs that formation and growth rates at Amman are similar to those at Finokalia, while lower values in Athens can be ascribed to a higher pre-existing particle number at this urban site. By comparing common NPF events there are 5 concomitant days between all three sites, highly related to air masses origin. Additionally, for another 19 days NPF takes place simultaneously between Finokalia and Amman, which also share common meteorological characteristics, adding to a total of 60% out of 41 NPF events observed at Finokalia, also simultaneously occurring in Amman.
Keywords: NPF, Eastern Mediterranean, particle number size distributions, concurrent regional events
Published in RUNG: 10.05.2024; Views: 107; Downloads: 3
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Abstract: Scyphozoa with symbionts have an advantage in oligotrophic environments due to the additional source of nutrients provided by their symbiontic algae, just as corals have benefits from their symbionts. The literature, however, has thus far devoted far less attention to the association between scyphozoan hosts and Symbiodinium sp. than it does to corals. This thesis investigated the identity of symbionts from scyphozoan medusae (Cotylorhiza tuberculata, Phyllorhiza punctata and Cassiopea xamachana) using a phylogenetic approach. Two scyphozoan species, P. punctata and C. tuberculata, were sampled over the Mediterranean Sea, while Cassiopea xamachana was sampled in the Atlantic Ocean. Symbionts were identified from live medusae and their identity and phylogenetic relationships were determined by analysing two nuclear markers, ITS2 and 28S rDNA, from symbionts. Symbiodinium sp. sequences belong to clades A, B, and C based on markers ITS2 and 28S rDNA. Moreover, individual medusae host only one type Symbiodinium (A, B or C). Host species from the Mediterranean Sea hosted Symbiodinium from clade A and B (C. tuberculata) or only from clade A (Phyllorhiza punctata), while the host from the Atlantic Ocean (C. xamachana) hosted Symbiodinium from clade B or C. The phylogeography of C. tuberculata medusae was analysed using mtCO1. All the haplotypes sampled over the Mediterranean Sea were clustered together without any sign of phylogeographic structuring.
Keywords: Scyphozoa, Cotylorhiza tuberculata, Symbiodinium sp., symbiosis, Mediterranean Sea, phylogeography, CO1, 28S rDNA, ITS regions
Published in RUNG: 03.10.2016; Views: 6317; Downloads: 370
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