81. 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: 352; Downloads: 2
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82. Particle number size distribution statistics at City-Centre Urban Background, urban background, and remote stations in Greece during summerS. Vratolis, Maria I. Gini, Spiros Bezantakos, Iasonas Stavroulas, Nikos Kalivitis, E. Kostenidou, E. Louvaris, D. Siakavaras, George Biskos, Nikolaos Mihalopoulos, 2019, original scientific article 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. Keywords: Mediterranean aerosol, particle number size distribution clustering, FLEXPART clustering Published in RUNG: 13.05.2024; Views: 299; Downloads: 0 This document has many files! More... |
83. Optical properties of near-surface urban aerosols and their chemical tracing in a Mediterranean city (Athens)Dimitris Katsanos, Aikaterini Bougiatioti, Eleni Liakakou, Dimitris G. Kaskaoutis, Iasonas Stavroulas, D. Paraskevopoulou, Maria Lianou, Basil E. Psiloglou, Evangelos Gerasopoulos, Christodoulos Pilinis, 2019, original scientific article Abstract: One-year measurements (October 2016–September 2017) of aerosol optical properties in the Athens urban environment were analyzed; for closure purposes, the results were supported by data of chemical composition of the non-refractory submicron aerosol fraction acquired with an Aerosol Chemical Speciation Monitor (ACSM). Both the spectral scattering (bsca) and absorption (babs) coefficients exhibit a pronounced annual variability with higher values (63.6 Mm–1 at 550 nm and 41.0 Mm–1 at 520 nm, respectively) in winter, due to domestic heating releasing increased carbonaceous emissions and the shallow mixing layer trapping aerosols near the surface. Much lower values (33.5 Mm–1 and 22.9 Mm–1 for bsca and babs, respectively) are found during summer, indicating rather aged aerosols from regional sources. The estimations of the dry spectral single scattering albedo (SSA), scattering (SAE) and absorption (AAE) Ångström exponents focus on the seasonality of the urban aerosols. The high SAE (~2.0) and low SSA (0.62 ± 0.11) values throughout the year indicate the dominance of fine-absorbing aerosols from fossil-fuel combustion, while the high AAE (~1.5) in winter suggests enhanced presence of biomass-burning aerosols. Pronounced morning and late evening/night peaks are found in both bsca and babs during winter, coinciding with the morning traffic rush hour and increased residential wood burning in the evening, while in the other seasons, the diurnal patterns flatten out. The wind speed strongly affects the aerosol loading and properties in winter, since for winds below 3 m s–1, a high increase in bsca and babs is observed, consistent with low dilution processes and hazy/smoggy conditions. Our closure experiments indicate a good agreement (R2 = 0.91, slope = 1.08) between the reconstructed and measured bsca values and reveal that organic matter contributes about half of the sub-micron mass in winter, followed by sulfate (~40%) and nitrate (10%, only in winter) aerosols. Keywords: urban aerosols, light scattering, absorption, chemical species, wood burning, Athens Published in RUNG: 10.05.2024; Views: 352; Downloads: 2
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84. Measurement of atmospheric black carbon in some South Mediterranean cities : seasonal variations and source apportionmentHamza Merabet, Rabah Kerbachi, Nikolaos Mihalopoulos, Iasonas Stavroulas, Maria Kanakidou, Noureddine Yassaa, 2019, original scientific article Abstract: This study aims to investigate, for the first time in Algeria, the atmospheric black carbon (BC) concentrations over one year measured at the Scientific Observatory of Algiers and to compare their concentration levels with other Mediterranean cities (i.e., Athens and Crete). The diurnal cycles as well as seasonal variations of BC concentrations were evaluated and attributed to their emission sources (fossil fuel: BCff and wood burning: BCwb). The annual mean concentrations of BC, BCff and BCwb were 1.113±2.030, 1.064±2.002 and 0.049±0.262 µgm-3, respectively. The highest seasonal mean concentrations were recorded in summer and autumn with 1.283±1.346 and 1.209±1.149 µgm-3 for BC and 1.217±1.431 and 1.177±1.151 µgm-3 for BCff, respectively. However, the lowest mean concentrations were recorded in winter and spring with 1.023±1.189 and 0.966±0.964 µgm-3 for BC and 0.933±1.177 and 0.956±0.874 µgm-3 for BCff, respectively. For BCwb, the highest mean concentrations were reached in winter and summer with 0.090±0.055 and 0.066±0.050 µgm-3, respectively, very likely due to the forest fires and long-range transport of air pollution from Europe. The lowest mean concentrations of BCwb were recorded in autumn and spring with 0.032±0.033 and 0.010±0.021 µgm-3, respectively. Seggregating BC levels into eight wind sectors, showed that the prevailing BC pollution with concentrations reaching up to 5.000 µgm-3 originated from the North-West wind sector. A source apportionment of BC for the wet and dry period was also perfomed followed by a back trajectory cluster analysis for long-range transport. Keywords: aerosol, black carbon, atmospheric pollution, source apportionment, seasonal variation, year modulation Published in RUNG: 10.05.2024; Views: 331; Downloads: 3
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85. Measuring the spatial variability of black carbon in Athens during wintertimeGeorgios Grivas, Iasonas Stavroulas, Eleni Liakakou, Dimitris G. Kaskaoutis, Aikaterini Bougiatioti, D. Paraskevopoulou, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2019, original scientific article Abstract: A first assessment of the spatial variability of ambient black carbon (BC) concentrations in the Greater Area of Athens (GAA) was carried out during an intensive wintertime campaign, when ambient levels are exacerbated by increased biomass burning for residential heating. Short-term daytime BC measurements were conducted at 50 sites (traffic and urban/suburban/regional background) and on-road along 12 routes. Daytime measurements were adjusted based on BC concentrations continuously monitored at a reference site. Indicative nighttime BC ambient concentrations were also measured at several residences across the area. Daytime BC concentrations recorded an average of 2.3 μg m-3 with considerable between-site variability. Concentrations at traffic sites were significantly higher (43% on average), compared with the rest of the sites. Varying levels were observed between background site subtypes, with concentrations at urban background sites (located near the center of Athens and the port of Piraeus) being 34% and 114% higher, on average, than at suburban and regional background sites, respectively. The traffic intensity at the nearest road and the population and built density in the surrounding area of sites were recognized as important factors controlling BC levels. On-road concentration measurements (5.4 μg m-3 on average) enabled the identification of hot-spots in the road network, with peak levels encountered along motorways (13.5 μg m-3 on average). Nighttime measurements demonstrated that wintertime BC pollution, enhanced by residential biomass burning for heating, affects the entire Athens basin. The reference site in central Athens was found to be representative of the temporal variability for daytime and nighttime BC concentrations at background locations. Keywords: mobile measurements, microaethalometer, Athens, mapping, traffic, biomass burning Published in RUNG: 10.05.2024; Views: 308; Downloads: 3
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86. Yearlong measurements of monoterpenes and isoprene in a Mediterranean city (Athens) : natural vs anthropogenic originAnastasia Panopoulou, Eleni Liakakou, Stéphane Sauvage, Valérie Gros, Nadine Locoge, Iasonas Stavroulas, Bernard Bonsang, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2020, original scientific article Abstract: Monoterpenes and isoprene are important constituents of the volatile organic compounds (VOCs) due to their high reactivity and participation in ozone and secondary aerosol formation. The current work focuses on the results of a 13-month intensive campaign of high resolution time-resolved measurements of these compounds, at an urban background site in Athens, Greece. On an annual basis, monoterpenes (α-pinene and limonene) surpass the isoprene levels presenting mean values of 0.70 ± 0.83 μg m−3, 0.33 ± 0.78 μg m−3 and 0.19 ± 0.36 μg m−3, respectively. The large standard deviation highlights the significant diurnal and day-to-day variability. Isoprene presents a typical seasonal cycle, with a photochemically induced summer-time maximum. Enhanced noon levels are observed during summer, whereas a morning peak in the autumn and winter profiles occurs, despite the generally low levels encountered during these seasons. The monoterpenes deviate from the expected biogenic pattern, presenting higher mean levels during the cold period and a night-to-early morning enhancement strongly related to local anthropogenic tracers such as BC, CO, NO or toluene, as well as increased levels under wind speeds lower than 3 m s−1. Estimations of the anthropogenic and biogenic fractions based on the enhancement ratios of α-pinene versus a variety of anthropogenic tracers, demonstrate a clear dominance of the anthropogenic sources in all studied seasons. Simultaneously, the biogenic fraction increased during summer relative to winter by more than 10 times. Both α-pinene and limonene significantly contribute to locally formed secondary organic aerosol (SOA), determined by means of an ACSM, accounting for at least 22% and 13% of their levels in summer and winter respectively. Additionally, monoterpenes and isoprene contribute 6% to the observed oxidants levels (O3 + NOx) during summer. Keywords: volatile organic compounds, biogenic compounds, monoterpenes, isoprene, Athens Published in RUNG: 10.05.2024; Views: 333; Downloads: 2
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87. Formation and growth of atmospheric nanoparticles in the eastern Mediterranean : results from long-term measurements and process simulationsNikos Kalivitis, Veli-Matti Kerminen, Giorgos Kouvarakis, Iasonas Stavroulas, Evaggelia Tzitzikalaki, Panayiotis Kalkavouras, Nikos Daskalakis, Stelios Myriokefalitakis, Aikaterini Bougiatioti, Hanna E. Manninen, 2019, original scientific article Abstract: Atmospheric new particle formation (NPF) is a common phenomenon all over
the world. In this study we present the longest time series of NPF records in
the eastern Mediterranean region by analyzing 10 years of aerosol number size
distribution data obtained with a mobility particle sizer. The measurements
were performed at the Finokalia environmental research station on Crete,
Greece, during the period June 2008–June 2018. We found that NPF took place
on 27 % of the available days, undefined days were 23 % and non-event
days 50 %. NPF is more frequent in April and May probably due to the
terrestrial biogenic activity and is less frequent in August. Throughout the
period under study, nucleation was observed also during the night. Nucleation
mode particles had the highest concentration in winter and early spring,
mainly because of the minimum sinks, and their average contribution to the
total particle number concentration was 8 %. Nucleation mode particle
concentrations were low outside periods of active NPF and growth, so there
are hardly any other local sources of sub-25 nm particles. Additional
atmospheric ion size distribution data simultaneously collected for more than
2 years were also analyzed. Classification of NPF events based on ion
spectrometer measurements differed from the corresponding classification
based on a mobility spectrometer, possibly indicating a different
representation of local and regional NPF events between these two measurement
data sets. We used the MALTE-Box model
for simulating a case study of NPF in the eastern Mediterranean region.
Monoterpenes contributing to NPF can explain a large fraction of the observed
NPF events according to our model simulations. However the adjusted
parameterization resulting from our sensitivity tests was significantly
different from the initial one that had been determined for the boreal
environment. Keywords: particles, number size distributions, new particle formation, regional background, SMPS, Eastern Mediterannean Published in RUNG: 10.05.2024; Views: 325; Downloads: 2
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88. Long-term variability, source apportionment and spectral properties of black carbon at an urban background site in Athens, GreeceEleni Liakakou, Iasonas Stavroulas, Dimitris G. Kaskaoutis, Georgios Grivas, D. Paraskevopoulou, Umesh Chandra Dumka, M. Tsagkaraki, Aikaterini Bougiatioti, K. Oikonomou, J. Sciare, 2020, original scientific article Abstract: This study aims to delineate the characteristics of Black Carbon (BC) in the atmosphere over Athens, Greece, using 4-year (May 2015–April 2019) Aethalometer (AE-33) measurements. The average BC concentration is 1.9 ± 2.5 μg m−3 (ranging from 0.1 to 32.7 μg m−3; hourly values), with a well-defined seasonality from 1.3 ± 1.1 μg m−3 in summer to 3.0 ± 4.0 μg m−3 in winter. Pronounced morning and evening/night peaks are found in the BC concentrations in winter, while during the rest of the seasons, this diurnal cycle appears to flatten out, with the exception of the morning traffic peak. On an annual basis, the biomass-burning fraction (BB%) of BC accounts for 22 ± 12%, while the fossil-fuel combustion (BCff) component (traffic emissions and domestic heating) dominates during summer (83%) and in the morning hours. BCwb exhibits higher contribution in winter (32%), especially during the night hours (39%). BC levels are effectively reduced by precipitation, while they significantly build-up for wind speeds <3 m s−1 and mixing-layer height (MLH) < 500 m. Normalizing the BC diurnal course by the MLH variations on a seasonal basis reveals that the residential wood-burning emissions are mostly responsible for the large BC increase during winter nights, whereas the low BC levels during daytime in the warm season are mainly attributed to dilution into a deeper MLH. BCwb is highly correlated with other BB tracers during winter nights (e.g. levoglucosan, non-sea-salt-K+, m/z 60 fragment), as well as with the fine fraction (PM2.5) OC and EC. The Delta-C, which represents the spectral dependence of BC as the absorption difference between 370 and 880 nm, is analyzed for the first time in Athens. It exhibits a pronounced seasonality with maximum values in winter night-time, and it appears as a valid qualitative marker for wood combustion. Keywords: black carbon, wood burning, source apportionment, mixing layer, biomass burning tracers, Athens Published in RUNG: 10.05.2024; Views: 311; Downloads: 1
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89. On the regional aspects of new particle formation in the Eastern Mediterranean : a comparative study between a background and an urban site based on long term observationsPanayiotis Kalkavouras, Aikaterini Bougiatioti, Georgios Grivas, Iasonas Stavroulas, Nikos Kalivitis, Eleni Liakakou, Evangelos Gerasopoulos, Christodoulos Pilinis, Nikolaos Mihalopoulos, 2020, original scientific article 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: 329; Downloads: 0 This document has many files! More... |
90. Integrating in situ measurements and city scale modelling to assess the COVID–19 lockdown effects on emissions and air quality in Athens, GreeceGeorgios Grivas, Eleni Athanasopoulou, Anastasia Kakouri, Jennifer Bailey, Eleni Liakakou, Iasonas Stavroulas, Panayiotis Kalkavouras, Aikaterini Bougiatioti, Dimitris G. Kaskaoutis, Michel Ramonet, 2020, original scientific article Abstract: The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real-world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7-week (23 March–10 May 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology-atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre- and post-lockdown 3-week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO2, black carbon (BC) and source-specific BC components. Models were run for pre-lockdown and lockdown periods, under baseline and reduced-emissions scenarios. The in-situ results indicate mean concentration reductions of 30–35% for traffic-related pollutants in Athens (NO2, CO, BC from fossil fuel combustion), compared to the pre-lockdown period. A large reduction (53%) was observed also for the urban CO2 enhancement while the reduction for PM2.5 was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO2 concentrations was reproduced by the implementation of the city scale model, under a realistic reduced-emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO2 mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants. Keywords: pandemic, urban air pollution, traffic, chemical transport model, TAPM, mapping Published in RUNG: 10.05.2024; Views: 355; Downloads: 2
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