Investigation of the chemical composition of the lower layer tropospheric aerosolsin the Eastern Mediterranean region: Implications regarding sources and long range transport

Abstract

oz DOĞU AKDENİZ BÖLGESİ AŞAĞI TROPOSFERİK PARÇACIKLARIN KİMYASAL YAPISININ İNCELENMESİ: KAYNAKLARA GÖRE YORUMLAR VE UZUN MENZİLLİ TAŞINIM KOÇAK, Mustafa Yüksek Lisans Tezi, Deniz Bilimleri Tez Yöneticisi: Doç. Dr. Nilgün Nezihe Kubilay Orta Doğu Teknik Üniversitesi Ocak 1996 ve Aralık 1998 tarihleri arasında Doğu Akdeniz'in Türkiye kıyısındaki Erdemli bölgesine ulasan hava kütlelerinden 409 adet aerosol örnekleri yüksek debili hava pompası kullanılarak toplanmıştır. Toplanan örneklerde atomik soğurma spektrofotometre ve iyon kromatografi cihazları kullanılarak sırası ile iz metaller (Al, Fe, Ca, Mn, Mg, Zn) ve sulu ortamda çözünebilen iyonlar (Cl`, Br`, N03`, S04=, C204=, CH3SO3`, Na+, NH4+, K+, Mg2+,Ca2+) ölçülmüştür. Buna ek olarak, örnekleme bölgesine (Erdemli) 900, 850, 700 ve 500 hPa barometrik basınç seviyelerinde ulaşan hava kütlelerinin üç günlük geriye dönük üç boyutlu yörüngeleri hesaplanmıştır. Elde edilen sonuçlar, Erdemli istasyonunda toplanan aerosol filtrelerinde ölçülen iz metal ve suda çözünebilen iyonların derişimlerindeki mevsimsel değişimlerin yerel yağışlarla yalandan ilgili olduğunu göstermiştir. Geçiş mevsimlerinde (ilkbahar ve sonbahar) yağışlar devam etmesine rağmen alüminyum- silikat yapısında zenginleşmiş elementlerin derişimlerinde ani yükselmeler görülmüştür. Faktör analizden ve zenginleşme katsayılarının hesaplanmasından elde edilen sonuçlar toprak, deniz ve antropojenik kaynaklı aerosollerin etkisinde olduğunu göstermiştir. Hava kütlelerinin üç günlük geri yörüngeleri ve biojeokimyasal izleyicilerin birlikte kullanılması toprak kaynaklı elementlerin ve gözlenen yüksek sülfat derişimlerinin kaynaklarım açıklamıştır. Örnekleme süresi boyunca 25 adet Afrika kaynaklı toz olayı tespit edilmiştir ve bu günlere ait örneklerdeki Al, Fe, Ca, Mn ve Zn derişimlerinde ani yükselmeler gözlenmiştir. Hesaplanan biyojenik sülfatın (%50'lere ulaşmakta) toplam sülfata katkısı, yaz aylarında birincil sülfat kaynağının çevre denizlerdeki (Akdeniz ve Karadeniz) biyolojik üretimden (DMS) kaynaklanabileceği fikrini ortaya çıkarmaktadır. VAnahtar kelimeler: aerosol, doğu Akdeniz, iz metaller, suda çözünebilir iyonlar, zenginleşme faktörü/diyagramı, faktör analizi, kaynaklar, geriye dönük hava kütleleri, uzun mesafeli taşınım VI

ABSTRACT INVESTIGATION OF CHEMICAL COMPOSITION OF THE LOWER TROPOSPHERIC AEROSOLS IN THE EASTERN MEDITERRANEAN REGION: IMPLICATIONS REGARDING SOURCES AND LONG-RANGE TRANSPORT KOÇAK, Mustafa M. Sc, in Marine Sciences Supervisor: Assoc. Prof. Dr. Nilgün Nezihe Kubilay Middle East Technical University March 2001 From January 1996 to December 1998 samples of 409 aerosols arriving at a rural site on the Turkish coast of the eastern Mediterranean (Erdemli) were collected by a hi- vol pump. The collected aerosol filter samples were analyzed by flame atomic absorption spectrophotometer and ion chromatography for trace elements (Al, Fe, Ca, Mg, Mn and Zn) and for water-soluble ions (CI`, Br`, N03`, S04=, C204=, CH3SO3`, Na+, NH4+, K+, Mg2+ and Ca2+), respectively. The combined data set provided concentration values for 17 elements and ions. In addition, three dimensional (3D), three days backward trajectories of air masses arriving daily at the Erdemli site at 900, 850, 700 and 500 hPa barometric pressure levels have been calculated to determine potential source regions. Analysis of lower layer and higher layer air mass trajectories indicated distinctly different potential source regions. The lower layer trajectories indicated that the dominating group of air masses originates from the west, north and east and accounting for 74% at 900 hPa and accounting for 72% at 850 hPa, respectively. The upper layer trajectories indicated a rapid transport from the south-southeasterly sector (the North African continent) have frequencies of 36% at 700 hPa and 61% at 500 hPa over the 10 year period. The results depicted that the seasonal variability of the atmospheric concentrations of the trace elements and ions determined at the Erdemli site was related to occurrence of precipitation. Atmospheric concentration of measured species (except marine elements) decreased to their minimum values during winter season due to precipitation scavenging, whereas, during dry summer months the lack of precipitation IIIresulted in the accumulation of aerosols in the atmosphere. During the transitional seasons, although there was still precipitation, the elements associated with mineral particles exhibited sporadic but intense concentration peaks. Air mass backward trajectories associated with geochemical tracer (Al) indicated that, throughout these seasons, incursion of Sahara dust governed the fluctuation in the atmospheric concentrations of the elements. The results obtained from factor analysis and enrichment factors suggested presence of three sources contributing to the determined concentrations. These were: crustal material, marine and anthropogenic sources. Furthermore, the results of factor analysis suggested that atmospheric aerosols over Cilisian Basin dominated by emissions of natural sources. Annually, 4%, 10%, 35% and 79% sea salt contribution were assessed on observed concentrations of Ca2+, S04=, K+ and Mg2+, respectively. The results obtained from biogeochemical tracers and air mass back trajectories showed the origin of the crustal elements and the detected high sulfate levels. During the period of sampling -25 African dust events were identified by an abrupt increase in the Al, Fe, Ca and also Mn and Zn concentration in the atmosphere. The average concentrations of the elements for the identified dates were calculated as 1569, 1 146, 5532, 17.9 and 27.9 ng m`3 for Al, Fe, Ca, Mn and Zn, respectively. The average concentrations of the same elements for the remaining samples (where there was no recorded mineral dust transport) were much lower (262, 255, 2212, 6.8 and 17.5 ng m`3 for Al, Fe, Ca, Mn and Zn, repectively). In addition, 3 -day back trajectory analysis indicate that air masses originating from Black Sea Region and Mediterranean Sea have MSA and nss-S04= values two times as much as than those calculated for air masses of samples originating from European and former Soviet Union. And elevated biogenic contributions to nss-SO/f in summer period (reaches up to 50%) suggest that there is major source of oceanic emissions of DMS in the eastern Mediterranean or surrounding seas (e.g. Black Sea). Keywords: aerosol, eastern Mediterranean, trace metals, water-soluble ions, enrichment factors/diagrams, factor analysis, air mass back trajectories, long range transport, Sahara, geobiochemical tracers. IV