Aerosols in the atmospheric boundary layer and its association with surface wind speed at a coastal site

A significant component of aerosol particles in the atmospheric boundary la yer is contributed by surface wind. A simple exponential function or a powe r-law is usually used to quantify this dependence. This is fairly valid ove r oceans where the background component is rather small. But over the coast , as a significant contribution to the background comes from the continent, which may not have the same wind speed dependence, it may be physically mo re meaningful to represent the aerosol system over the coast as the sum of two components, one being the background and the other contributed by sea b reeze. The wind speed dependence of aerosol scattering coefficient in the a tmospheric boundary layer at a tropical coastal station is studied in the l ight of the above hypothesis, using the data obtained from a bistatic conti nuous wave lidar. The observed aerosol scattering coefficient at a fixed al titude is represented as the sum of two components, one being the backgroun d and the other depending on the current wind speed having a power-law type wind dependence. The seasonal and altitude pattern of the two components a re studied. It is seen that in this coastal site, during the monsoon season , on average, approximately 25% of the mixing region aerosol optical depth is contributed by the sea breeze. The seasonal pattern of the background co mponent shows a marked difference within and above the a ell mixed region. A comparison of mixing region aerosol optical depth has shown that similar to 30% of the columnar aerosol optical depth comes from the lowest 1 km reg ion of the atmosphere. (C) 1998 Elsevier Science Ltd. All rights reserved.