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Optical Properties of Near-surface Urban Aerosols and their Chemical Tracing in a Mediterranean City (Athens)

Category: Aerosol and Atmospheric Chemistry

Article In Press
DOI: 10.4209/aaqr.2017.11.0544
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Dimitris Katsanos1, Aikaterini Bougiatioti2,3, Eleni Liakakou1, Dimitris G. Kaskaoutis1, Iasonas Stavroulas1,4, Despina Paraskevopoulou1, Maria Lianou1, Basil E. Psiloglou1, Evangelos Gerasopoulos1, Christodoulos Pilinis5, Nikolaos Mihalopoulos 1,2

  • 1 IERSD, National Observatory of Athens, Lofos Koufou, Palaia Penteli, 15236 Athens, Greece
  • 2 Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003 Crete, Greece
  • 3 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 4 Energy Environment and Water Research Center, The Cyprus Institute, Nicosia 2121, Cyprus
  • 5 Department of Environment, University of Aegean, Mytilene 81100, Greece

Highlights

Very high scattering and absorption coefficients in Athens during winter nighttime.
Significant impact of domestic heating wood burning to aerosol properties in winter.
Primary CO, NOx emissions coincide well with the aerosol scattering and absorption.
Significant agreement of reconstructed scattering from chemistry with observations.


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


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