Abstract
Abstract. Atmospheric particle size distributions were measured on Crete island, Greece in the Eastern Mediterranean during an intensive field campaign between 28 August and 20 October, 2005. Our instrumentation combined a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS) and measured number size distributions in the size range 0.018 μm–10 μm. Four time periods with distinct aerosol characteristics were discriminated, two corresponding to marine and polluted air masses, respectively. In marine air, the sub-μm size distributions showed two particle modes centered at 67 nm and 195 nm having total number concentrations between 900 and 2000 cm−3. In polluted air masses, the size distributions were mainly unimodal with a mode typically centered at 140 nm, with number concentrations varying between 1800 and 2900 cm−3. Super-μm particles showed number concentrations in the range from 0.01 to 2.5 cm−3 without any clear relation to air mass origin. A small number of short-lived particle nucleation events were recorded, where the calculated particle formation rates ranged between 1.1–1.7 cm−3 s−1. However, no particle nucleation and growth events comparable to those typical for the continental boundary layer were observed. Particles concentrations (Diameter <50 nm) were low compared to continental boundary layer conditions with an average concentration of 300 cm−3. The production of sulfuric acid and its subsequently condensation on preexisting particles was examined with the use of a simplistic box model. These calculations suggested that the day-time evolution of the Aitken particle population was governed mainly by coagulation and that particle formation was absent during most days.
Highlights
During the past decades, atmospheric research has been concerned with the global distribution of atmospheric aerosol particles because of their effects on global climate by interaction with the incoming solar radiation (Haywood and Boucher, 2000; Lohmann and Feichter, 2005), their oxidation capacity of the atmosphere (Ravishankara, 1997), and their adverse effects on human health (HEI, 2002; WHO, 2004)
Several limitations of the model need to be kept in mind during the discussion of the simulation results: The absence of condensable species beyond H2SO4, no new particle formation was considered during the mid-day observation period, the requirement of a quasi Lagrangian observation, i.e., no significant air mass changes were accounted for during the simulation period
An intensive field study was conducted at the environmental research station Finokalia of the University of Crete, Greece, in order to better understand the variability and climatic relevance of atmospheric particles in the Eastern Mediterranean
Summary
Atmospheric research has been concerned with the global distribution of atmospheric aerosol particles because of their effects on global climate by interaction with the incoming solar radiation (Haywood and Boucher, 2000; Lohmann and Feichter, 2005), their oxidation capacity of the atmosphere (Ravishankara, 1997), and their adverse effects on human health (HEI, 2002; WHO, 2004). N. Kalivitis et al.: Particle size distributions in the Eastern Mediterranean troposphere irradiance with the sea water in the marine environment results in high levels of relative humidity (RH), that causes aerosols to take up water and contribute significantly to direct radiative forcing even in the absence of clouds. In situ observations of particle number size distributions in the Eastern Mediterranean are important for evaluation of these processes, they are scarce, and have been limited to restricted periods in urban areas (e.g. Petajaet al., 2007). To better understand the variability and climatic role of aerosols in Eastern Mediterranean, intensive measurements of atmospheric aerosol particles were conducted between August and October 2005 at a remote location on Crete Island (ARIADNE – Aerosol Physical and Chemical Identification on Crete). Additional results from the campaign, such as the hygroscopic particle properties and chemical particle composition will be presented in a separate paper
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