N.: Optical properties of atmospheric aerosol in Maritime Environments

• Main Authors: Alexander Smirnov, Yoram J. Kaufman, Thomas F. Eck, Ilya Slutsker, Christophe Pietras, Rangasayi N. Halthore
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; Aerosol Robotic Network
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.487.5188; http://gacp.giss.nasa.gov/publications/special/smirnov2.pdf

Systematic characterization of aerosol over the oceans is needed to understand the aerosol effect on climate and on transport of pollutants between continents. We report the results of a comprehensive optical and physical characterization of ambient aerosol in 5 key island locations of the Aerosol Robotic Network (AERONET) of sun and sky radiometers, spanning over 2-5 years. The results are compared with aerosol optical depths and size distributions reported in the literature over the last 30 years. Aerosol found over the tropical Pacific Ocean (at 3 sites between 20°S and 20°N), still resembles mostly clean background conditions dominated by maritime aerosol. The optical thickness is remarkably stable with mean value of τa(500 nm)=0.07, mode value at τam=0.06 and standard deviation of 0.02 to 0.05. Average Ångström exponent ranged from 0.3 to 0.7 characterizes the wavelength dependence of the optical thickness. Over the tropical to subtropical Atlantic (2 stations at 7°S and 32°N) the optical thickness is significantly higher: τa(500 nm)=0.14 and τam=0.10 due to the frequent presence of dust, smoke and urban/industrial aerosol. For both oceans the atmospheric column aerosol is characterized by a bimodal log-normal size distribution