Abstract
Abstract. In this study, we investigate the mode resolved density of ultrafine atmospheric particles measured in boreal forest environment. The method used here enables us to find the distinct density information for each mode in atmospheric fine particle population: the density values for nucleation, Aitken, and accumulation mode particles are presented. The experimental data was gained during 2 May 2005–19 May 2005 at the boreal forest measurement station "SMEAR II" in Hyytiälä, Southern Finland. The density values for accumulation mode varied from 1.1 to 2 g/cm3 (average 1.5 g/cm3) and for Aitken mode from 0.4 to 2 g/cm3 (average 0.97 g/cm3). As an overall trend during the two weeks campaign, the density value of Aitken mode was seen to gradually increase. With the present method, the time dependent behaviour of the particle density can be investigated in the time scale of 10 min. This allows us to follow the density evolution of the nucleation mode particles during the particle growth process following the nucleation burst. The density of nucleation mode particles decreased during the growth process. The density values for 15 nm particles were 1.2–1.5 g/cm3 and for grown 30 nm particles 0.5–1 g/cm3. These values are consistent with the present knowledge that the condensing species are semi-volatile organics, emitted from the boreal forest.
Highlights
Atmospheric aerosol contains a complex mixture of particles of the natural and the anthropogenic origin, consisting of both primary and secondary particles from a variety of sources (e.g. Seinfeld and Pandis, 1998)
The separation of atmospheric aerosol particles into different modes is based on the assumption that the modes have different origins (e.g. Seinfeld and Pandis, 1998)
The Aitken and the accumulation mode particle densities had the lowest values in the beginning of the campaign, i.e. during the first period, when no particle formation occurred
Summary
Atmospheric aerosol contains a complex mixture of particles of the natural and the anthropogenic origin, consisting of both primary and secondary particles from a variety of sources (e.g. Seinfeld and Pandis, 1998). Atmospheric aerosol contains a complex mixture of particles of the natural and the anthropogenic origin, consisting of both primary and secondary particles from a variety of sources Its chemical and elemental composition, optical, hygroscopic and other phys-. The assessment of the climatic and the adverse health effects of atmospheric aerosol particles requires detailed information on particle properties (Yu et al, 2006; Lohmann and Feichter, 2005; Pope and Dockery, 2006). The particle size and chemical composition affect the particle residence time in the atmosphere, its optical properties and its potential to act as a cloud condensation nuclei as well as its behaviour in human lungs. The chemical composition and other chemical and physical properties of the particles carry information concerning sources and the formation mechanisms of particles
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