Atmospheric pollution concentrations over the Eastern Mediterranean during summer – A review

Abstract

<p><strong>Abstract.</strong> The Eastern Mediterranean (EM) is one of the regions in the world where elevated concentrations of primary and secondary gaseous air pollutants have been reported frequently, mainly in summer. This review discusses published studies of the atmospheric dispersion and transport conditions characterizing this region during the summer, followed by a description of some essential studies dealing with the corresponding concentrations of air pollutants such as ozone, carbon monoxide, total reactive nitrogen, methane and sulfate aerosols observed there. <br><br> The interlaced relationship between the downward motion of the subsiding air aloft induced by global circulation systems affecting the EM and the depth of the Persian Trough, a low-pressure trough that extends from the Asian monsoon at the surface controlling the spatio-temporal distribution of the mixed boundary layer during summer is discussed. The strength of the wind flow within the mixed layer and its depth affect much the amount of pollutants transported and determine the potential of the atmosphere to disperse contaminants off their origins in the EM. The reduced mixed layer and the accompanying weak westerlies, characterizing the summer in this region, lead to reduced ventilation rates, preventing an effective dilution of the contaminants. Several studies pointing at specific local (e.g. ventilation rates) and regional peculiarities (long-range transport) enhancing the building up of pollutant concentrations are presented. <br><br> Tropospheric ozone concentrations observed in the summer over the EM are among the highest over the Northern Hemisphere. The three essential processes controlling its formation (i.e., long- range transport of polluted air masses, dynamic subsidence at mid-tropospheric levels, and stratosphere-to-troposphere exchange) are reviewed. Airborne campaigns and satellite-borne initiatives have indicated that the concentration values of reactive nitrogen identified as precursors in the formation of ozone over the EM were found to be 2 to 10 times higher than in the hemispheric background troposphere. Several factors favor sulfate particulate abundance over the EM. Models, aircraft measurements, and satellite derived data, have clearly shown that sulfate has a maximum during spring and summer over the EM. The carbon monoxide (CO) seasonal cycle, as obtained from global background monitoring sites in the EM is mostly controlled by the tropospheric concentration of the hydroxyl radical (OH), and therefore demonstrates high concentrations over winter months and the lowest during summer when photochemistry is active. Modeling studies have shown that the diurnal variations in CO concentration during the summer result from long-range CO transport from European anthropogenic sources, contributing 60 to 80 % of the boundary-layer CO over the EM. The values retrieved from satellite data enable us to derive the spatial distribution of methane (CH<sub>4</sub>), identifying August as the month with the highest levels over the EM. The outcomes of a recent extensive examination of the distribution of methane over the tropospheric Mediterranean Basin, as part of the Chemical and Aerosol Mediterranean Experiment (ChArMEx) program, using model simulations and satellite measurements is coherent with other previous studies. Moreover, this methane study provides some insights on the role of the Asian monsoon anticyclone in controlling the variability of CH<sub>4</sub> pollutant within mid-to-upper tropospheric levels above the EM in summer.</p>

An example of aerosol pattern variability over bright surface using high resolution MODIS MAIAC: The eastern and western areas of the Dead Sea and environs

“…The winter (December-February) and fall (September-November) months have a lower seasonal mean AOD, while during the summer we see a concentration of somewhat higher values around the western coast of the Dead Sea, where the northwestern wind penetrates the Negev, bringing humidity and air masses from the densely-populated industrial coast of central Israel as well as from Europe (Derimian et al, 2006). Previous studies has found that during this season and at this location, fine particle loadings with anthropogenic origin are dominant (Derimian et al, 2006;Dayan et al, 2017).…”

“…During the summer season, the persistent Persian Trough system cause local stability beneath the seasonal strong inversion layer at about 1 km above mean-sea-level. This allows the Mediterranean sea breeze to influence the area greatly alongside its unique topography, by enhancing the impact of local emission sources (Kishcha et al, 2016;Alpert et al, 1997;and Dayan et al, 2017) and transporting dust and anthropogenic aerosols from afar (Derimian et al, 2006;Derimian et al 2017). Specifically, Derimian et al (2017) have shown that chemical composition, microphysical and optical properties of atmospheric aerosol deep inland in the Negev Desert of Israel were found to be influenced by daily occurrences of sea breeze flow from the Mediterranean Sea.…”

Polybrominated diphenyl ethers (PBDEs) in background air around the Aegean: implications for phase partitioning and size distribution

“…In addition, previous studies in this area revealed higher particle-phase PBDEs levels in summer than in winter (Besis et al 2015;Besis et al 2016;Cetin and Odabasi 2008;Gevao et al 2013). The reduced mixed layer and the weak west winds, characterizing the summer in Eastern Mediterranean, lead to reduced ventilation rates, preventing an effective dilution of the contaminants (Dayan et al 2017). The present study presents the G/P partitioning of PBDEs, their mass size distribution, and explores the long-range transport potential during an intensive 2week summertime sampling campaign concurrently carried out at four quasi-background sites around the Aegean Sea.…”