engleski

Chemical Characterization of the Sea Surface and Ambient Marine Aerosols of Middle Adriatic Area During Spring and Summer Seasons

The current knowledge in aerosol science is still incapable of giving a real and quantitative assessment of their actual impact on the global climate and the human health. This problem arises from the insufficient understanding of aerosol sources, their formation mechanisms, chemical composition and properties. Organic matter (OM) is an important atmospheric fraction which enters the atmosphere through biogenic and anthropogenic emissions. However, the composition of atmospheric OM and the respective source apportionment are far less known than those of the inorganic part of the atmospheric particulate matter (PM). The lack of information about atmospheric organic species lies in their complexity and low concentrations in general [1]. Many of the organics identified in the atmospheric aerosols are known to be surface active in aqueous solutions, contributing to the aerosol water soluble organic carbon (WSOC) pool [2]. Surface active substances (SAS) or surfactants present in the atmosphere influence the climate by reducing the surface tension of the air-droplet interface, affecting physical properties of aqueous droplets in the air. Being amphiphilic organic compounds, SAS are also highly enriched in the upper part of the sea surface, known as a sea surface microlayer (SML) [3], which represents the largest interface on the Earth. Therefore, the sea surface has a global role in exchanging marine OM with the atmosphere and a combined interdisciplinary SML and aerosol study could provide new knowledge on the linkage between the sea and the atmosphere. Thus, a comprehensive physical-chemical study of both, marine aerosols and sea surface samples (SML and corresponding underlayer water (ULW) from 0.5 m depth) collected simultaneously during spring and summer 2015 at the Rogoznica Lake, central Dalmatia, Croatia, has been performed. Water soluble organic matter of aerosol, SML and ULW samples was analysed. SAS were determined by electrochemical methods and the total organic carbon (TOC) and dissolved organic carbon (DOC) by high temperature catalytic oxidation (HTCO) technique. Ionic composition was studied by ion chromatography (IC). Spring aerosol samples were characterized by lower PM mass, TOC, WSOC, SAS and inorganic ion concentrations (F- , Cl- , Br- , NO2 - , NO3 - , SO4 2 , PO4 3- , Na+ , K+ , NH4 + ) in comparison to the summer samples. At the same time, higher enrichment factors (EFs) were obtained for particulate and dissolved organic carbon, nutrients and SAS of the spring SML samples, indicating a recent phytoplankton bloom and accumulation of OM within the SML. Intense biological activity most likely influenced the atmospheric PM during the spring season, whereas the aerosols from the summer period were highly affected by the local biomass burning events (significant correlation of PM mass with K+ ions) as well as by secondary photo-oxidation processes (indicated by elevated WSOC/OC ratios as well as the content of dicarboxylic acids and SAS).

marine aerosols ; sea surface microlayer

This work was also supported by the Slovenian Research Agency project (Contract no. P1-0034- 0140)