Showing papers by "George Biskos published in 2013"

Chemical composition and hygroscopic properties of aerosol particles over the Aegean Sea

Abstract: . The chemical composition and water uptake characteristics of sub-micrometre atmospheric particles over the region of the Aegean Sea were measured between 25 August and 11 September 2011 within the framework of the Aegean-Game campaign. High temporal-resolution measurements of the chemical composition of the particles were conducted using an airborne compact time-of-flight aerosol mass spectrometer (cToF-AMS). These measurements were performed during two flights from the island of Crete to the island of Lemnos and back. A hygroscopic tandem differential mobility analyser (HTDMA) located on the island of Lemnos was used to measure the ability of the particles to take up water. The HTDMA measurements showed that the particles in the dominant mode were internally mixed, having hygroscopic growth factors that ranged from 1.00 to 1.59 when exposed to 85% relative humidity. When the aircraft flew near the ground station on Lemnos, the cToF-AMS measurements showed that the organic volume fraction of the particles ranged from 43 to 56%. These measurements corroborate the range of hygroscopic growth factors measured by the HTDMA during that time. Good closure between HTDMA and cToF-AMS measurements was achieved when assuming that the organic species were less hygroscopic and had an average density that corresponds to aged organic species. Using the results from the closure study, the cToF-AMS measurements were employed to determine vertical profiles of a representative aerosol hygroscopic parameter κmix. Calculated κmix values ranged from 0.19 to 0.84 during the first flight and from 0.22 to 0.80 during the second flight. Air masses of different origin as determined by back trajectory calculations can explain the spatial variation in chemical composition and κmix values of the particles observed in the region.

Physical and Chemical Processes of Polluted Air Masses During Etesians: Aegean-Game Airborne Campaign – An Outline

Abstract: Gaseous species and aerosol size distribution and chemical composition within the boundary layer during the Etesians is investigated, based upon airborne measurements, over the Aegean Sea, from Crete to Limnos islands (29/8–8/9 2011, Aircraft_BAe146–FAAM) Three flights of a similar route covered the eastern and western parts of the Aegean Sea Two flights were performed on the same day to study the impact of the diurnal cycle The sorties involved horizontal tracks mainly at 150 m asl and above the aerosol layer, at 25 km asl, and profiles up to 45 km near the ground stations of Crete and Limnos and the Central Aegean Sea Marked variations were detected in the vertical structure of aerosols and thermodynamic variables between the eastern and western segments flown around the Aegean Several discrete aerosol layers, separated by a clean slot, containing particles of different chemical composition were observed, with sulfates and organics being the dominant components CO concentrations ranged from 80 ppb above the mixing layer, up to 140 ppb near the surface O3 ranged between 50 and 75 ppb, with higher values observed at surface upwind of Finokalia and in the mixing layer in Central and Northern Aegean Sea

Comparison Between the Theoretical and Experimental Performance of a Differential Mobility Analyzer with Three Monodisperse-Particle Outlets

Abstract: Differential mobility analyzers (DMAs) with more than one monodisperse-particle outlet can offer a number of advantages compared to conventional single monodisperse-particle outlet designs. A generalized theoretical model and experimental measurements describing the performance of a DMA with 3 monodisperse-particle outlets have been independently reported in the literature. The objective of this article is to compare the theoretical predictions with the measurements. Resolutions determined by the theoretically predicted transfer functions for the three monodisperse-particle outlets are compared with measurements when the DMA was operated under different operating conditions. Predictions and measurements show good agreement when the DMA is operated at low sheath flow rates and for aerosol outlets relatively far from the aerosol inlet. For aerosol outlets relatively near the inlet there is evidence that the discrepancy between theoretical predictions and measurements may disappear at higher sheath flow rate...

Air Pollution in Eastern Mediterranean: Nested-Grid GEOS-CHEM Model Results and Airborne Observations

Abstract: Trace gases concentrations in the boundary layer (BL) and the free troposphere are studied in the Eastern Mediterranean based on an updated nested-grid application of GEOS-CHEM global model and airborne observations that were collected over the Greek territory during the AEGEAN GAME airborne field campaign in September 2011. Modelled concentrations are studied against measurements along the flight tracks. Moreover, the spatial distribution of the pollutants over the study domain is examined in relation to the prevailing wind regime. The role of the long-range transport of pollution is investigated particularly through the northern and eastern boundaries due to the prevailing NE circulation. It is found that the model captures adequately carbon monoxide (CO) and ozone (O3) levels within the troposphere. CO and O3 concentrations over the Aegean Sea can exceed the background levels attributed either to transport downwind the local sources or to long range transport particularly from the northern and eastern part of the domain under the strong NE Etesian winds.