Date

2018-7-26

Author

Tutsak, Ersin

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Long-term aerosol optical and micro physical properties obtained from AERONET sun/sky radiometer situated at the rural coastal site of Eastern Mediterranean between January 2000 and December 2014 were analyzed. Moreover, concentrations of SO42-, NH4+, NO3- (in PM2.5) and their precursor gases (SO2, NH3 and HNO3) were measured with a near real-time Ambient Ion Monitor-Ion Chromatography instrument in winter and summer of 2015. Air flow arriving at 1 km and 4 from Eastern Europe and Western Europe showed a negative trend from 2000 to 2014, decreasing about 0.2 % per year. In contrast, air flow arriving at 1 km (4km) from North Africa and Turkey demonstrated a positive trend throughout the study period, increasing 0.15 (0.40) % and 0.29 (0.15) % per year, respectively. The arithmetic mean AOT decreased 2.5 times from 440 nm (0.30) to 1020 nm (0.12), indicating the dominance of fine particles. AOT and α illustrated a large short-term variability, varying up to couple of fold from day to day. The lowest AOT values were chiefly found in winter owing to the removal of particles by rain. Enhanced AOT values at 440 nm were detected in spring with low α440-870 primarily due to mineral dust intrusions from North Africa and the Middle East. High AOT at 440 nm and α440-870 were principally characterized in summer because of high gas-to particle conversion, sluggish air masses and absence of rain. Elevated AOT with relatively lower α (0.7) and fine mode fraction (47 %) were observed when the air flow originated from North Africa (SAH) and the Middle East (MID). Regarding the relationship between AOT and Water Vapor (WV) as a function of α, three classes of aerosol were identified, namely, non-hygroscopic, moderately hygroscopic and hygroscopic. Potential source contribution function (PSCF) exhibited that non-hygroscopic particles were associated with mineral dust dominated aerosol population, originating from North Africa and the Middle East. Moderately hygroscopic particles were a mixture of mineral dust and anthropic aerosols due mainly to arrival of the dust after travelling over industrialized and populated sites (such as Spain, France and Italy). On the other hand, any particular potential source area couldn’t be defined for hygroscopic particles, showing nearly mesoscale formation of secondary aerosols under the prevailing summer conditions. Imaginary part of the refractive index, single scattering albedo, absorption angstrom exponent for dust, mixed and pollution events showed distinct difference. The imaginary part of refractive index for dust event fluctuated from 2.5 x 10-3 to 2.0 x 10-3 between 870 and 1020 nm and for wavelengths between 675 nm and 440 nm the imaginary part of refractive index augmented from 4.3 x 10-3 to 11.0 x 10-3. Although similar spectral behavior was observed, the imaginary part of the refractive index at 440 nm for mixed event was 2.2 times lesser than that of mineral dust event. For pollution event, the imaginary part of refractive index slightly increased from 5.0 x 10-3 at 440 nm to 6.3 x 10-3 at 1020 nm. Aerosol type were classified into three groups namely dust, mixed and anthropic according to extinction angstrom exponent. The comparison of the microphysical properties of the three aerosol type revealed that categorization of the aerosol type based on extinction angstrom exponent was insufficient. The classification of aerosol type by applying cluster analysis to optical properties presented relatively better results. The aerosol absorption optical thickness at 440 nm and the imaginary part of the refractive index were statistically larger for Period II (2005-2009) compared to Period I (2000-2004) and III (20010-2014) due to the to the higher influence of dust intrusion from desert areas during Period II. Of the water-soluble ions in PM2.5, sulfate and ammonium were the prevailing species. Arithmetic mean sulfate and ammonium concentrations were respectively 2814 ng m-3 and 1371 μg m-3. Aerosol nitrate arithmetic mean was 495 ng m-3. Among the precursor gases, ammonia exhibited the highest concentration with a value of 3330 ng m-3. Sulfur dioxide and nitric acid concentrations were 879 ng m-3 and 346 ng m-3, respectively. Regarding arithmetic means of gas-to-particle conversion ratios for sulfate (0.62), ammonium (0.38) and nitrate (0.50), it might be suggested that the concentrations of these species were mainly influenced by non-local sources. Taking into account this study and historic off-line measurements, there was a decreasing trend for sulfate, nitrate and their precursor gases in the Eastern Mediterranean.

Subject Keywords

Aerosol optical and physical properties, hygroscopic behavior, SSA, AAOT, refractive index, aerosol type,, SO42-, NH4+, NO3-, NH3, HNO3, Eastern Mediterranean

URI

https://hdl.handle.net/11511/95086

Collections

Graduate School of Marine Sciences, Thesis