Abstract
Abstract. The main objective of this study is the identification of major factors controlling levels and chemical composition of aerosols in the regional background (RB) along the Mediterranean Basin (MB). To this end, data on PM levels and speciation from Montseny (MSY, NE Spain), Finokalia (FKL, Southern Greece) and Erdemli (ERL, Southern Turkey) for the period 2001 to 2008 are evaluated. Important differences on PM levels and composition are evident when comparing the Western and Eastern MBs. The results manifest W-E and N-S PM10 and PM2.5 gradients along the MB, attributed to the higher frequency and intensity of African dust outbreaks in the EMB, while for PM1 very similar levels are encountered. PM in the EMB is characterized by higher levels of crustal material and sulphate as compared to WMB (and central European sites), however, RB nitrate and OC + EC levels are relatively constant across the Mediterranean and lower than other European sites. Marked seasonal trends are evidenced for PM levels, nitrate (WMB), ammonium and sulphate. Also relatively higher levels of V and Ni (WMB) are measured in the Mediterranean basin, probably as a consequence of high emissions from fuel-oil combustion (power generation, industrial and shipping emissions). Enhanced sulphate levels in EMB compared to WMB were measured. The high levels of sulphate in the EMB may deplete the available gas-phase NH3 so that little ammonium nitrate can form due to the low NH3 levels. This study illustrates the existence of three very important features within the Mediterranean that need to be accounted for when modeling climate effects of aerosols in the area, namely: a) the increasing gradient of dust from WMB to EMB; b) the change of hygroscopic behavior of mineral aerosols (dust) via nitration and sulfation; and c) the abundance of highly hygroscopic aerosols during high insolation (low cloud formation) periods.
Highlights
Tropospheric aerosols have been the object of intensive research mainly because of their impact on health (Pope and Dockery, 2006), the Earth’s climate (IPCC, 2007), visibility, ecosystems and building materials
PM in the EMB is characterized by higher levels of crustal material and sulphate as compared to WMB, regional background (RB) nitrate and OC + EC levels are relatively constant across the Mediterranean and lower than other European sites
This study aims to summarise the results on levels and chemical composition of RB-PM along the Mediterranean Basin, with special attention giving to the comparison between WMB and EMB, in order to identify and discriminate the major controlling factors
Summary
Tropospheric aerosols have been the object of intensive research mainly because of their impact on health (Pope and Dockery, 2006), the Earth’s climate (IPCC, 2007), visibility, ecosystems and building materials. Air quality degradation by particulate matter (PM) over polluted areas is often characterized by high levels of regional background (RB) aerosols on which intense episodes of either natural or anthropogenic origins are superimposed. Such episodes are associated with synoptic and mesoscale meteorological conditions that favour formation and accumulation of aerosol pollutants at regional or even continental scales. Measurements performed at RB sites, seem to optimize accurate documentation on both aerosol long-term trends and relevant synoptic features. The importance of this type of measurement site is highlighted by the creation of the EU-wide EUSAAR network
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