1. Yearlong variability of oxidative potential of particulate matter in an urban Mediterranean environmentD. Paraskevopoulou, Aikaterini Bougiatioti, Iasonas Stavroulas, T. Fang, Maria Lianou, Eleni Liakakou, Evangelos Gerasopoulos, R. Weber, Athanasios Nenes, Nikolaos Mihalopoulos, 2019, original scientific article Abstract: The oxidative potential (OP) of fine and coarse fractions of ambient aerosols was studied in the urban environment of Athens, Greece. OP was quantified using a dithiothreitol (DTT) assay, applied to the water soluble fraction of aerosol that was extracted from 361 fine and 84 coarse mode of 24-h and 12-h filter samples over a one-year period. During the cold period, samples were collected on a 12-h basis, to assess the impact of night-time biomass burning emissions from domestic heating on OP. The chemical characteristics of aerosols were measured in parallel using an Aerosol Chemical Speciation Monitoring (ACSM) and a 7-wavelength Aethalometer. A source apportionment analysis on the ACSM data resulted in the identification of organic aerosol (OA) factors on a seasonal basis. A good correlation of OP with NO3−, NH4+, BC (Black Carbon), Organics and LV-OOA (low volatility oxygenated OA) was found during winter, revealing the importance of combustion and aging processes for OP. During the summertime, a good correlation between OP and SO4−2 and NH4+indicates its association with regional aerosol – thus the importance of oxidative aging that reduces its association with any characteristic source. Multiple regression analysis during winter revealed that highly oxygenated secondary aerosol (LV-OOA) and, to a lesser extent, fresh biomass burning (BBOA) and fossil fuel (HOA) organic aerosol, are the prime contributors to the OP of fine aerosol, with extrinsic toxicities of 54 ± 22 pmol min−1 μg−1, 28 ± 7 and 17 ± 4 pmol min−1μg−1, respectively. In summer, OP cannot be attributed to any of the identified components and corresponds to a background aerosol value. In winter however, the regression model can reproduce satisfactorily the water soluble DTT activity of fine aerosol, providing a unique equation for the estimation of aerosol OP in an urban Mediterranean environment.
Keywords: oxidative potential, reactive oxygen species, DTT assay, particulate matter, urban aerosol
Published in RUNG: 13.05.2024; Views: 191; Downloads: 0
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2. Regional new particle formation as modulators of cloud condensation nuclei and cloud droplet number in the eastern MediterraneanPanayiotis Kalkavouras, Aikaterini Bougiatioti, Nikos Kalivitis, Iasonas Stavroulas, Maria Tombrou, Athanasios Nenes, Nikolaos Mihalopoulos, 2019, original scientific article 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: 206; Downloads: 2
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