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1.
Emission of volatile organic compounds from residential biomass burning and their rapid chemical transformations
Maximillien Desservettaz, Michael Pikridas, Iasonas Stavroulas, Aikaterini Bougiatioti, Eleni Liakakou, Nikolaos Hatzianastassiou, Jean Sciare, Nikolaos Mihalopoulos, Efstratios Bourtsoukidis, 2023, original scientific article

Abstract: Biomass combustion releases a complex array of Volatile Organic Compounds (VOCs) that pose significant challenges to air quality and human health. Although biomass burning has been extensively studied at ecosystem levels, understanding the atmospheric transformation and impact on air quality of emissions in urban environments remains challenging due to complex sources and burning materials. In this study, we investigate the VOC emission rates and atmospheric chemical processing of predominantly wood burning emissions in a small urban centre in Greece. Ioannina is situated in a valley within the Dinaric Alps and experiences intense atmospheric pollution accumulation during winter due to its topography and high wood burning activity. During pollution event days, the ambient mixing ratios of key VOC species were found to be similar to those reported for major urban centres worldwide. Positive matrix factorisation (PMF) analysis revealed that biomass burning was the dominant emission source (>50 %), representing two thirds of OH reactivity, which indicates a highly reactive atmospheric mixture. Calculated OH reactivity ranges from 5 s−1 to an unprecedented 278 s−1, and averages at 93 ± 66 s−1 at 9 PM, indicating the presence of exceptionally reactive VOCs. The highly pronounced photochemical formation of organic acids coincided with the formation of ozone, highlighting the significance of secondary formation of pollutants in poorly ventilated urban areas. Our findings underscore the pressing need to transition from wood burning to environmentally friendly sources of energy in poorly ventilated urban areas, in order to improve air quality and safeguard public health.
Keywords: biomass burning, urban air quality, VOCs, emission factors, source apportionment
Published in RUNG: 13.05.2024; Views: 314; Downloads: 1
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2.
Yearlong variability of oxidative potential of particulate matter in an urban Mediterranean environment
D. 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: 267; Downloads: 0
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3.
Sources and processes that control the submicron organic aerosol composition in an urban Mediterranean environment (Athens) : a high temporal-resolution chemical composition measurement study
Iasonas Stavroulas, Aikaterini Bougiatioti, Georgios Grivas, D. Paraskevopoulou, M. Tsagkaraki, Pavlos Zarmpas, Eleni Liakakou, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2019, original scientific article

Abstract: Submicron aerosol chemical composition was studied during a year-long period (26 July 2016–31 July 2017) and two wintertime intensive campaigns (18 December 2013–21 February 2014 and 23 December 2015–17 February 2016), at a central site in Athens, Greece, using an Aerosol Chemical Speciation Monitor (ACSM). Concurrent measurements included a particle-into-liquid sampler (PILS-IC), a scanning mobility particle sizer (SMPS), an AE-33 Aethalometer, and ion chromatography analysis on 24 or 12 h filter samples. The aim of the study was to characterize the seasonal variability of the main submicron aerosol constituents and decipher the sources of organic aerosol (OA). Organics were found to contribute almost half of the submicron mass, with 30 min resolution concentrations during wintertime reaching up to 200 µg m−3. During winter (all three campaigns combined), primary sources contributed about 33 % of the organic fraction, and comprised biomass burning (10 %), fossil fuel combustion (13 %), and cooking (10 %), while the remaining 67 % was attributed to secondary aerosol. The semi-volatile component of the oxidized organic aerosol (SV-OOA; 22 %) was found to be clearly linked to combustion sources, in particular biomass burning; part of the very oxidized, low-volatility component (LV-OOA; 44 %) could also be attributed to the oxidation of emissions from these primary combustion sources. These results, based on the combined contribution of biomass burning organic aerosol (BBOA) and SV-OOA, indicate the importance of increased biomass burning in the urban environment of Athens as a result of the economic recession. During summer, when concentrations of fine aerosols are considerably lower, more than 80 % of the organic fraction is attributed to secondary aerosol (SV-OOA 31 % and LV-OOA 53 %). In contrast to winter, SV-OOA appears to result from a well-mixed type of aerosol that is linked to fast photochemical processes and the oxidation of primary traffic and biogenic emissions. Finally, LV-OOA presents a more regional character in summer, owing to the oxidation of OA over the period of a few days.
Keywords: ACSM, organic aerosol, PMF, source apportionment
Published in RUNG: 13.05.2024; Views: 275; Downloads: 2
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4.
Regional new particle formation as modulators of cloud condensation nuclei and cloud droplet number in the eastern Mediterranean
Panayiotis 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: 315; Downloads: 2
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5.
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: 303; Downloads: 2
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6.
Measuring the spatial variability of black carbon in Athens during wintertime
Georgios 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: 290; Downloads: 3
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7.
Formation and growth of atmospheric nanoparticles in the eastern Mediterranean : results from long-term measurements and process simulations
Nikos 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: 286; Downloads: 2
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8.
Long-term variability, source apportionment and spectral properties of black carbon at an urban background site in Athens, Greece
Eleni 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: 283; Downloads: 1
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9.
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 observations
Panayiotis 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: 290; Downloads: 0
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10.
Integrating in situ measurements and city scale modelling to assess the COVID–19 lockdown effects on emissions and air quality in Athens, Greece
Georgios 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: 309; Downloads: 2
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