Abstract
Abstract. The size distribution of atmospheric aerosols plays a key role for understanding and quantifying the uncertainties related to aerosol–radiation and aerosol–cloud interactions. These interactions ultimately depend on the size distribution through optical properties (such as aerosol optical depth, AOD) or cloud microphysical properties. Hence, the main objective of this contribution is to disentangle the impact of the representation of aerosol size distribution on aerosol optical properties over central Europe, particularly over the Mediterranean Basin, during a summertime aerosol episode. To fulfill this objective, a sensitivity test has been conducted using the coupled chemistry–meteorology model WRF-Chem (Weather Research Forecast model coupled with Chemistry). The test modified the parameters defining a lognormal size distribution (geometric diameter and standard deviation) by 10 %, 20 %, and 50 %. Results reveal that the reduction in the standard deviation of the accumulation mode leads to the largest impacts on AOD due to a transfer of particles from the accumulation mode to the coarse mode. A reduction in the geometric diameter of the accumulation mode also has an influence on AOD representation since particles in this mode are assumed to be smaller. In addition, an increase in the geometric diameter of the coarse mode produces a redistribution through the total size distribution by relocating particles from the finer modes to the coarse.
Highlights
Aerosol size distribution is, among others, a key property of atmospheric aerosols that largely determines how they interact with radiation and clouds
A question arising from the results presented so far relies on which modification presents the highest sensitivity for modifying aerosol optical depth (AOD), and how the modifications implemented in the GOCART aerosol scheme compare with observations
The main objective of this contribution is to study the impact of the representation of aerosol size distribution on aerosol optical properties over central Europe, over the Mediterranean Basin, during summertime
Summary
Among others, a key property of atmospheric aerosols that largely determines how they interact with radiation and clouds Aerosol optical properties, such as the scattering phase function, single-scattering albedo, and aerosol optical depth (AOD), strongly depend on the aerosol size distribution (Eck et al, 1999; Haywood and Boucher, 2000; Romakkaniemi et al, 2012; Obiso et al, 2017; Obiso and Jorba, 2018). Atmospheric aerosols influence climate forcing through aerosol–cloud interactions (ACIs) These interactions produce an impact on clouds and precipitation that is connected to the number concentration of particles, which can act as cloud condensation nuclei (CCN) and ice nuclei (IN). These condensation nuclei depend on the aerosol size distribution and composition (Andreae and Rosenfeld, 2008; Romakkaniemi et al, 2012)
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