Articles | Volume 16, issue 17
Atmos. Chem. Phys., 16, 11219–11236, 2016
https://doi.org/10.5194/acp-16-11219-2016

Special issue: CHemistry and AeRosols Mediterranean EXperiments (ChArMEx)...

Atmos. Chem. Phys., 16, 11219–11236, 2016
https://doi.org/10.5194/acp-16-11219-2016

Research article 12 Sep 2016

Research article | 12 Sep 2016

Long-term visibility variation in Athens (1931–2013): a proxy for local and regional atmospheric aerosol loads

Dimitra Founda1, Stelios Kazadzis2,1, Nikolaos Mihalopoulos1,3, Evangelos Gerasopoulos1, Maria Lianou1, and Panagiotis I. Raptis1 Dimitra Founda et al.
  • 1Institute for Environmental Research & Sustainable Development, National Observatory of Athens, Athens, Greece
  • 2Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, Davos, Switzerland
  • 3Department of Chemistry, University of Crete, Heraklion, Greece

Abstract. This study explores the interdecadal variability and trends of surface horizontal visibility at the urban area of Athens from 1931 to 2013, using the historical archives of the National Observatory of Athens (NOA). A prominent deterioration of visibility in the city was detected, with the long-term linear trend amounting to −2.8 km decade−1 (p < 0.001), over the entire study period. This was not accompanied by any significant trend in relative humidity or precipitation over the same period. A slight recovery of visibility levels seems to be established in the recent decade (2004–2013). It was found that very good visibility (>  20 km) occurred at a frequency of 34 % before the 1950s, while this percentage drops to just 2 % during the decade 2004–2013. The rapid impairment of the visual air quality in Athens around the 1950s points to the increased levels of air pollution on a local and/or regional scale, related to high urbanization rates and/or increased anthropogenic emissions on a global scale at that period. Visibility was found to be negatively/positively correlated with relative humidity/wind speed, the correlation being statistically valid at certain periods. Wind regime and mainly wind direction and corresponding air mass origin were found to highly control visibility levels in Athens. The comparison of visibility variation in Athens and at a non-urban reference site on Crete island revealed similar negative trends over the common period of observations. This suggests that apart local sources, visibility in Athens is highly determined by aerosol load of regional origin. AVHRR and MODIS satellite-derived aerosol optical depth (AOD) retrievals over Athens and surface measurements of PM10 confirmed the relation of visibility to aerosol load.

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Short summary
Historical time series are unique sources of information for past climate and atmospheric composition change. The 82-year time series of visibility data collected at the National Observatory of Athens (NOA) was an excellent proxy for the long-term evolution of particulate pollution in the eastern Mediterranean, at times when direct aerosol measurements were missing. Evolution of particulate pollution of both local and regional origin is nicely reflected on visibility records of NOA.
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