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

Abstract

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.

Prediction of source contributions to urban background PM<sub>10</sub> concentrations in European cities: a case study for an episode in December 2016 using EMEP/MSC-W rv4.15 and LOTOS-EUROS v2.0 – Part 1: The country contributions

“…LOTOS-EUROS explicitly accounts for cloud chemistry by computing sulfate formation as a function of cloud liquid water content and cloud droplet pH as described in Banzhaf et al (2012). For aerosol chemistry the thermodynamic equilibrium module ISORROPIA II is used (Fountoukis and Nenes, 2007).…”

Long-Term Observed Visibility in Eastern Thailand: Temporal Variation, Association with Air Pollutants and Meteorological Factors, and Trends

“…The relationship between visibility and PM 10 , was analyzed in three ways: (a) correlation analysis; (b) mean PM 10 under different visibility classes; and (c) weekday and weekend differences. Visibility classes (e.g., poor and good) have often been used in visibility assessment [14,45], offering convenience in public communication and also partially reducing the effect of changed visibility targets. As suggested by the US EPA (1987) [43], visibility classes were selected based on yearly frequency, with the lowest upper limit (of visibility target) found over a period of time used as the best visibility Atmosphere 2019, 10, 122 8 of 24 class and the remaining classes based qualitatively on their frequency and separation.…”

Long-term series and trends in surface solar radiation in Athens, Greece

“…Under near-clear-sky conditions, these percentages are −7 % and +9 % for the dimming and brightening periods, respectively. Similarly, Founda et al (2016) analyzed long-term SD and total cloud cover time series over 15 sites in Greece (the oldest one beginning in 1897). They showed an increase in SD at almost all stations since the mid-1980s, which in certain areas of southeastern Greece amounts to an increase of 20 h year −1 .…”