Study of aerosol optical thickness in Hong Kong, validation, results, and dependence on meteorological parameters

Three years of aerosol optical thickness (AOT) measured from 2002 to 2004 in Hong Kong using a ground-based sky radiometer is reported. Comparison of the ground-based optical thickness measurement with the MODIS satellite AOT using a linear regression analysis confirmed the integrity of the ground-based data quality. The MODIS optical thickness obtained from AQUA and TERRA correlates with the sky radiometer data with linear correlation coefficient, R², values of 0.804 and 0.625, respectively. Annual mean ground-based AOT at visible channels have increased by 33% and 22% for observations at 400 and 500 nm, respectively. Monthly mean turbidity coefficient varies from 0.20 to 0.56 over the period, while the monthly mean of the Angstrom exponent ranges from 0.12 to 1.34. The variation is due to seasonal nature of the aerosols. Fitting the annual mean AOT values to the Angstrom's equation has revealed a significant 53% increase in the Angstrom exponent (from 0.7 to 1.07) over the three-year period, while the turbidity remains comparable.