Abstract
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.
Highlights
Atmospheric aerosol particles affect the global radiative balance of the earth by directly absorbing and scattering solar radiation, and indirectly by acting as cloud condensation nuclei
Good closure between cToF-AMS and hygroscopic tandem differential mobility analyser (HTDMA) measurements was achieved when the aircraft flew in the vicinity of the ground station
Measurements of the chemical composition and hygroscopicity of atmospheric particles were conducted over the region of the Aegean Sea using a cToF-AMS onboard the FAAM BAe-146 aircraft, and a ground-based HTDMA system located on a remote station on the island of Lemnos
Summary
Atmospheric aerosol particles affect the global radiative balance of the earth by directly absorbing and scattering solar radiation (i.e. direct effect; Haywood and Boucher, 2000), and indirectly by acting as cloud condensation nuclei (i.e. indirect effect; Ogren and Charlson, 1992). S. Bezantakos et al.: Chemical composition and hygroscopic properties of aerosol particles species or mixtures of organic and inorganic compounds, existing knowledge does not allow accurate predictions of their hygroscopicity. Bezantakos et al.: Chemical composition and hygroscopic properties of aerosol particles species or mixtures of organic and inorganic compounds, existing knowledge does not allow accurate predictions of their hygroscopicity This limited understanding is one of the greatest uncertainties in determining the role of atmospheric aerosols on climate
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