22 Feb 2022
22 Feb 2022
Status: this preprint is currently under review for the journal ACP.

Long-term visibility variation at the Ebro Observatory (1960–2020)

Juan José Curto1 and Nicolás Tacoronte1,2 Juan José Curto and Nicolás Tacoronte
  • 1Observatorio del Ebro, (OE) CSIC – Universitat Ramón Llull
  • 2Universidad Complutense de Madrid

Abstract. This study explores the interdecadal variability and trends of surface horizontal visibility in the Baix Ebre area (Spain) from 1960 to 2020, using the historical archive of the Ebro Observatory located in the town of Roquetes, in the centre of the region. We detected a prominent improvement in visibility in the first decades of the second part of the twentieth century but this was followed by a dramatic deterioration in the last decade recorded (2010–2020). This was not accompanied by a significant trend in relative humidity over the same period. It was found that very good visibility (20–50 km) occurred at a frequency of more than 40 % in the 1980s and 90s, while this percentage dropped to just 15 % during the 2010–2020 decade.

Visibility was found to be negatively correlated with relative humidity and positively correlated with wind speed. This correlation was statistically valid for most of the time periods we looked at. Wind regime, prevailing wind direction and the corresponding origin (marine or continental) of the air mass were found to display a strong influence on the short-term visibility levels at the Ebro Observatory. However, long term visibility trends are controlled by other factors, which are probably of anthropogenic origin. The rapid increase in population in Roquetes and other neighbouring towns during recent decades could be the cause of the implicit impairment of air quality observed because of increased levels of air pollution on a regional scale. Apart from these local sources, visibility at the Ebro Observatory could also be influenced by the aerosol load from neighbouring regions (Castelló and Tarragona) which have a significant concentration of industries.

Juan José Curto and Nicolás Tacoronte

Status: open (extended)

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Juan José Curto and Nicolás Tacoronte

Juan José Curto and Nicolás Tacoronte


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Short summary
Long term variation of surface horizontal visibility is a clear indicator of atmospheric quality and it does not depend on any measurement device susceptible of lack of calibration. In this paper we present visibility series measured at Ebro Observatory (Spain), in the western part of Mediterranean area. Although these observations being performed in a priori “clean” location, no natural causes can explain the visibility trends and the anthropogenic activity is the most probable cause.