A Comparison and Summary of Aerosol Optical Properties as Observed from Aircraft, Ship and Land During ACE-Asia

In-situ measurements of aerosol optical properties were made from multiple research platforms during the ACE-Asia experiment, which took place between March 31 and May 04, 2001. A focus of these measurements was to constrain the optical properties of pollutants and desert dust in the region of China, Korea and Japan so that they can be more accurately represented in radiative forcing models. Each of the platforms involved in ACE-Asia covered a different geographic area and, in some cases, different vertical segments of the atmosphere. The most comprehensive set of information can thus be gained by combining this suite of measurements. First, however, we need to test whether these platforms made equivalent measurements of the aerosol optical properties. This is done by comparing visible-wavelength scattering, absorption, hemispheric backscatter, light scattering hygroscopic growth, Angstrom exponent, hemispheric backscatter fraction, single scatter albedo, and light scattering fine mode fraction as measured in-situ from four of the ACE-Asia platforms: the National Center for Atmospheric Research C-130; the Office of Naval Research Center for Interdisciplinary Remotely-Piloted Aircraft Studies Twin Otter; the National Oceanographic and Atmospheric Administration's ship R.V. Ron Brown; and the South Korean surface station Gosan on Jeju Island. Results will be shown for both direct inter-platform comparisons and for comparisons of campaign-wide data sets. Based on the discrepancies seen in the direct inter-platform comparisons we can infer how much of the difference in the campaign-wide data sets can be attributed to instrumental discrepancies and how much to real differences in the atmospheric aerosol sampled by the platforms. This analysis serves two purposes: 1) it helps us identify biases or errors in any given platform's data set and 2) it helps us to understand how accurately each platform's measurements can be extrapolated to represent the broader ACE-Asia study region. For the C-130, Ron Brown and Gosan data sets optical properties were separately measured for the sub- and super-micron aerosol. This allows us to take cases where the fine mode fraction of scattering, FMF_scat, was high and define the optical properties of pollution from the sub-micron data set. Similarly, we take cases where FMF_scat was low and define the optical properties of dust using the super-micron data set. Finally, we show how the optical properties of the total aerosol change as a function of FMF_scat. Our sub-micron and super-micron data can be used directly in a model for the optical properties of the fine and coarse mode aerosol, respectively. Also, modelers can use sub-micron versus total mass fractions and mass scattering efficiencies to calculate FMF_scat then compare their calculated optical properties as a function of FMF_scat against our measured relationships.