Modeling the contribution of secondary aerosols on aerosol scattering ensemble: a comparative analysis of the scattering abilities of different aerosol species
Geoengineering News
Abstract
Atmospheric transport processes and conditions can cause primary aerosols to interact, giving rise to secondary aerosols with unique chemical and physical properties. These new species of aerosols can potentially influence the light-scattering properties of the aerosol ensemble and thus the climate system in ways that are not yet fully understood. In this study, the effects of different aerosol types on the scattering of incident solar radiation are modeled and the contribution of secondary aerosols to the aerosol scattering ensemble is highlighted. Using the discrete dipole approximation method, the scattering properties of freshwater droplets, sea salts (liquid, dry, and wet solids), ice crystals, clay minerals, clay particles coated with a thin film of water and sea salt droplets, black carbon (BC), and a complex particle of clay, sea salt, and BC with sulphate coating are calculated and compared. The calculations assume a spherical particle shape model for marine aerosols, a distorted cube for wet salts and ice, and a distorted ellipse with an induced surface roughness length for terrestrial aerosols at a size parameter of x=5 and a wavelength range of 400 to 750 nm. The results show that tiny ice crystals trapped in freshwater droplets are the most efficient atmospheric scatterers, followed by sea salt droplets, while BC absorbs the most compared to other aerosols studied. On average, the atmospheric interaction between marine and terrestrial aerosols is able to enhance atmospheric light scattering and polarisation by aerosols compared to terrestrial aerosols. This study suggests that the scenario in which there are many freshwater aerosols in the atmosphere can be very healthy for the Earth’s system compared to other aerosols. Therefore, we suggest that when formulating the radiative properties of aerosols in climate models, the scenarios of dominant freshwater aerosols and the contribution of secondary aerosols should not be ignored. The results presented here may be useful in the fields of Geoengineering and Aerosol-cloud microphysics.
Fig. 1. Shape of marine aerosols (a) used to model sea salt and freshwater droplet, (b) is the shape used to model wet salt and wet ice, (c) is the scenario where there is a mixture of the ice-crystal and liquid phase in the atmosphere, (d) is the shape used to model dry salt grains and frozen water (snowlike particles). (e) is the shape of the terrestrial aerosol (dust, BC), (f) is the scenario where a dust particle is trapped in a molecule of water or sea salt droplet, and (g) is the scenario where we consider a sulphate particle internally mixed with clay mineral, BC, and sea salts