| Popis: |
This thesis presents the analysis and results of aerosol physical and optical properties over Darwin, Australia, a coastal tropical site which is affected by smoke aerosols from biomass burning inland and sea salt aerosols brought in by the sea breeze. Continuous Multi Filter Rotating Shadow Radiometer (MFRSR) spectral measurements for the period March 2002 -June 2003, have been obtained from the Tropical Western Pacific facilities site in Darwin, part of the D.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program. Atmospheric optical thickness was obtained using the Langley regression analysis and aerosol optical thickness was then obtained by removing the molecular and ozone contributions from the total atmosphere optical thickness. A regression analysis was performed on the aerosol optical thickness and the Angstrom exponent to identify the trends in seasonality. It shows a strong seasonal cycle with low optical thickness in autumn and high optical thickness in spring, coinciding with the peak of the biomass burning season. The aerosol optical thickness data were inverted using the Constrained Linear Inversion technique to obtain the size distributions. A novel method, combining several different criteria, was used for classification of the size distribution into classes which could be related to biomass burning aerosols and sea salt aerosols. These classes showed variations with season and meteorological parameters. The wind diurnal cycle showed a significant signature on the aerosol size and loading, and the aerosol loading was also strongly linked to fire activity. The aerosols observed over Darwin reflected different proportions of biomass and sea salt and variations in size over the whole year. The seasonal pattern in the aerosol properties over Darwin is found to be owing to the location of Darwin in the Tropical Warm Pool and the variety of aerosol types: smoke particles produced by the dry season burning conditions, and the sea salt aerosols associated with the introduction of cleaner maritime westerly and northwesterly winds. Aerosols are also affected by the high rainfall rate during the wet season, which washes out the aerosols from the atmosphere. |
