engleski

CHARACTERIZATION OF ORGANIC MATTER IN MARINE AEROSOLS NEAR EUTROPHIC SEAWATER ECOSYSTEM (ROGOZNICA LAKE, CENTRAL DALMATIA) DURING WINTER SEASON

In spite of decades of investigations, the effects of atmospheric aerosols via cloud formation and properties still constitutes the largest uncertainties in assessing the climate budget today [1]. These difficulties result in part from the limited understanding of the microphysical processes controlling the transformations of atmospheric aerosol particles into cloud droplets. Organic matter (OM) is an important atmospheric fraction which enters the atmosphere through biogenic emissions and anthropogenic sources. Many of the organics identified in the atmospheric aerosols are known to be surface active in aqueous solutions contributing to aerosol water soluble organic carbon (WSOC) pool [2]. Surface active substances (SAS) or surfactants become in focus of atmospheric research nowadays as they can substantially influence the surface tension of the gas-liquid interface of solution droplets in the air which plays a critical role in governing their cloud condensation nuclei (CCN) abilities. SAS as the most reactive part of natural organic matter are also enriched in the airsea interface area known as the sea surface microlayer [3]. This millimetre thin layer represents widespread gelatinous and biofilm-like environment which exists even at higher than global average wind speeds. This created a new perspective of the air-water interface and its global role in exchanging marine OM with atmosphere. Thus, the impact of the SML on CCN formation through injection of surface active material from the SML to the atmosphere may be of global significance. A progressive approach to understanding the SML and hence its role in global biogeochemistry can only be achieved by considering all the key components of this complex environments an integrated whole. Thus combined interdisciplinary SML and aerosol study seems to be a promising approach to contributing to the knowledge on the linkage between the SML properties and cloud formation and climate. We selected unique, highly eutrophic, euxinic marine lake system Rogoznica Lake in central Dalmatia (Middle Adriatic, 43o 32’N 15o 58’E) as one of the important study sites. Extreme and fluctuating environmental conditions affecting water column stratification related to salinity, temperature, redox conditions ; mixing with high periodical supply of nutrient and sulphur species, indicate that the marine ecosystem Rogoznica Lake is extreme, naturally eutrophic system which feels all effects of the Adriatic atmospheric and ocean conditions. Influence of these conditions due to the lake semi-closed nature might be several times stronger than in other coastal and open sea Adriatic waters [4]. In order to get better insights into OM characteristics and dynamics between the atmosphere and the marine system this study is designed to comprise seasonal data of the marine aerosols as well as the SML and underlaying water samples (ULW, from 0.5 m depth) at the Rogoznica Lake. Here we will present first results of our winter (01-02 2015) campaign. The aerosol samples (aerodynamic diameter <2.5 μm) were collected on GF/F filters (φ=47 mm) by low volume sampler (2.3 m3 /h, sampling time: 24 h). The SML samples were collected by the Garrett screen method using the stainless steel screen Isolation and characterization of the water soluble organic matter (WSOM) from aerosol, SML and ULW samples by determining the SAS using electrochemical techniques as well as determining the total organic carbon (TOC) and dissolved organic carbon (DOC) by high temperature catalytic oxidation (HTCO) technique were conducted. Our preliminary results indicate that SMLs were enriched with TOC and SAS on average 6.6 and 2.1, respectively, if compared with ULW samples. The contribution of dissolved OC to the TOC pool was in range from 53 to 97% for the SML samples. Concentrations of the aerosol mass fluctuated from around 2.5 to 18.2 μg/m3 . The average concentration (5.5 μg/m3 ) is comparable to the PM2.5 values presented for several regional background sites in Europe. Organic matter represents, on average, approximately 3.8% of the aerosol mass. The average OC concentrations in this study are compared with those from other marine enviromnents over the world. To get more insight to the seasonal variability of predominant surfactant material in marine aerosols, obtained SAS concentrations (expressed in equivalent amounts of model surfactant T-X-100, mg/l) were normalized to the dissolved organic carbon content and corelated with normalized surfactant activities obtained for different model organic compounds as presented in Figure 1. Results will be discussed in relation to the previous data of different environmental systems, regions and seasons.

marine aerosols ; sea surface microlayer

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