The Impact of Molecular Interactions on Atmospheric Aerosol Radiative Forcing

The Impact of Molecular Interactions on Atmospheric Aerosol Radiative Forcing 

Shawn M. Kathmann, Gregory K. Schenter and Bruce C. Garrett  

Aerosol radiative forcing is nonlinearly dependent on surface albedo, aerosol composition and size distribution, relative humidity, and solar angle [1]. Albedo is simply the ratio of reflected to incident electromagnetic radiation (e.g., fresh clean 

The impact of secondary aerosols on indirect radiative forcing is the most variable and is the least understood [3]. The reasons why the indirect effect of secondary aerosols is so difficult to describe is that it depends upon [1] (1) a series of molecular-microphysical processes that connect aerosol nucleation to cloud condensation nuclei to cloud drops and then ultimately to cloud albedo and (2) complex cloud-scale dynamics on scales of 100-1000 km involve a consistent matching of multiple spatial and time scales and are extremely difficult to parameterize and incorporate in climate models. Nucleation changes aerosol particle concentrations that cause changes in cloud droplet concentrations, which in turn, alter cloud albedo. Thus, macro-scale cloud properties that influence indirect forcing result from both micro-scale and large-scale dynamics. To date, the micro-scale chemical physics has not received the appropriate attention. 

FIGURE 20.2 Illustration of the size (below particle) and number of molecules (upper right) in atmospheric particles ranging from critical clusters up to cloud drops. The visible spectrum is shown to emphasize the size range (0.1 to 1.0 mm) relevant to aerosol radiative forcing. Nucieation creates new particles that evolve into larger particles relevant to aerosol radiative 

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