Influence of submicron aerosol composition upon atmospheric extinction in coastal areas

摘要

Abstract: Measurements of sub-micron aerosol particles in southern California coastal areas during the Electro-Optical Propagation Assessment in Coastal Environments program indicate that not only particle concentrations but also the composition of the aerosol is highly variable due to the range of particular and pre-cursor gaseous sources present in the littoral zone. Frequently, in offshore flow, large quantities of soot carbon resulting from fossil fuel burning are mixed with pervasive sulphate aerosol particles, while in onshore flow, significant numbers of sea spray particles are present. At larger particle sizes, the aerosol spectrum may be dominated by sea spray particles produced by the action of the wind on the ocean surface at moderate and high wind speeds. This situation is further complicated along coasts where breaking surf provides an additional source of sea spray, and where offshore breezes may transport aeolian dusts from the land interior. These measurements demonstrate that land-sea breezes and other local meteorological processes give rise to substantial variations in aerosol characteristics on relatively small temporal and spatial scales and, from this knowledge of particulate composition, aerosol refractive indices and, hence, atmospheric extinctions at visible and IR wavelengths have been derived for various environmental conditions. !12