Barbara Winter

Thesis Approved December 1994

Light Scattering by a Sea Salt Aerosol Layer

When the "global warming" predictions first surfaced, an intense study of the response of the earth-atmosphere-aerosol system began. Before trying to understand the system as a whole, however, it is essential to know the relative importance of the different factors within it. So far, research on the radiative properties of aerosols has targeted mainly anthropogenically produced aerosol. The purpose of the present work is to determine how much of the planetary clear sky albedo is due to the layer of sea salt aerosol that exists over the oceans. This is done by solving the two-stream approximation to the radiative transfer equation, and applying the thin-layer limit of the solution to the sea salt layer. The result is used to calculate Delta F - the change in solar flux entering at the top of the atmosphere - corresponding to the aerosol's contribution to the clear-sky albedo. It is shown that Delta F for sea salt aerosol is opposite in sign and comparable in magnitude to the predicted radiative forcing by increased levels of CO_2. Since sea salt is a stable component of the atmosphere, its radiative effects are included in any measurement or calculation of the current planetary albedo. But when studying climates with strong winds (leading to a greater sea salt aerosol loading), it is important to factor in the greater cooling due to sea salt, as an omission of this effect would lead to an underestimate of the planetary albedo.