Coarse mode optical information retrievable using ultraviolet to short-wave infrared Sun photometry: Application to United Arab Emirates Unified Aerosol Experiment data

Abstract

The United Arab Emirates Unified Aerosol experiment provided a unique opportunity for testing aerosol retrieval algorithms in conditions where the optical influence of coarse mode particles was significant. Comparisons between Aerosol Robotic Network (AERONET) Sun photometry retrievals of a previously reported spectral deconvolution algorithm (SDA) and surface-based microphysical and optical measurements showed levels of correlation suggestive of moderate vertical homogeneity for (extensive) measures of fine and coarse mode aerosol particles and stronger vertical homogeneity for indicators of (intensive) aerosol type. An extension of the SDA into the short-wave infrared (SDA+) was developed in order to exploit the enhanced coarse mode information available in new AERONET instruments which include a 1.64 m channel. Comparisons between values of coarse mode Angstrom exponent (αc (1.64 μm)) retrieved from SDA+ and effective (coarse mode) radius derived from AERONET inversions showed moderate but significant correlations. Correlations between coarse mode effective radius derived from αc (1.64 μm) and surface-based volume mean diameter estimates underscored the physical significance of the spectral retrievals and suggested moderate vertical homogeneity in terms of coarse mode particle size.