Atmospheric Particles

The atmosphere of the Earth is a system that we do not fully understand. As has been recognized by the Intergovernmental Panel on Climate Change (IPCC), one of its greatest uncertainties is the role of suspended particles. Atmospheric particles can alter the chemical composition of the atmosphere by providing sites for heterogeneous reactions. In addition, once large enough to be optically active, they influence the radiative properties of the atmosphere and thus directly affect the Earth's climate at regional and global scales. The larger particles also indirectly affect the climate of our planet through their action on cloud formation.

Atmospheric nanoparticles (i.e., particles having diameter less than 100 nm) represent the great majority of the global aerosol in terms of number concentration, and due to their small size they exhibit different properties compared to larger particles of the same composition. For example, phase transitions of inorganic nanoparticles from the solid to the liquid state (deliquescence) can be different from those of their large-particle counterparts because the relative contribution of the surface energy to the total free energy of the particle-vapor system increases markedly for sub-100 nm particles. In addition, the hygroscopic growth of these particles (i.e., the growth of the particles due to water vapor condensation) decreases markedly with decreasing size as a result of the Kelvin effect (cf. Biskos et al. 2006), and/or the presence of less hygroscopic compounds on the particles as shown in Fig. 1.

Elucidating the physicochemical mechanisms that involve suspended nanoparticles in the atmosphere is therefore of great importance in atmospheric chemistry and global climate change. Our primary goal is to probe the intrinsic properties of airborne nanoparticles observed in urban and remote environments and understand the transformations they undergo while suspended in the atmosphere. We try to achieve that be combining field measurements with laboratory experiments that aim to simulate the real-life atmospheric conditions. The results from our studies are then used in Atmospheric models aiming to quantify that impact of aerosols on climate. 

Figure 1. Phase transitions and hygroscopic growth of atmospheric aerosol particles at 298 K. The lines show predicted growth factors for (a) pure (NH4)2SO4 particles having any diameter greater than 60 nm (black solid line), (b) pure 10-nm (NH4)2SO4 particles (red dashed line), and (c) 10-nm (NH4)2SO4 particles mixed with less hygroscopic compounds (green dashed-dotted line). The curves at the right top corner of the figure show the respective activation curves of the particles.

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