Aerosol Properties Computed from Aircraft-Based Observations During the ACE-Asia Campaign: 2. A Case Study of Lidar Ratio Closure

Abstract

For a vertical profile with three distinct layers (marine boundary, pollution, and dust layers), observed during the ACE-Asia campaign, we carried out a comparison between the modeled lidar ratio vertical profile and that obtained from co-located airborne NASA AATS-14 sunphotometer and shipborne Micro-Pulse Lidar (MPL) measurements. The vertically resolved lidar ratio was calculated from two size distribution vertical profiles-one obtained by inversion of sunphotometer-derived extinction spectra, and one measured in-situ-combined with the same refractive index model based on aerosol chemical composition. The aerosol model implies single scattering albedos of 0.78-0.81 and 0.93-0.96 at 0.523 μm (the wavelength of the lidar measurements), in the pollution and dust layers, respectively. The lidar ratios calculated from the two size distribution profiles agree closely in the dust layer; they are however, significantly lower than the lidar ratios derived from combined lidar and sunphotometer measurements. Uncertainties in aerosol size distributions and refractive index only partly explain these differences, suggesting that particle nonsphericity in this layer is an additional explanation. In the pollution layer, the two size distribution profiles yield lidar ratios that agree within the MPLNET is funded by the NASA Earth Observing System and Radiation Sciences Program. We would like to thank Jens Redemann for his detailed review of an earlier version of the manuscript and helpful comments. We would also like to thank the anonymous reviewers for their valuable comments and suggestions.Address correspondence to M. Kuzmanoski, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia. E-mail: mkuzm@phys.unsw.edu.au estimated uncertainties. The retrieved size distributions result in a lidar ratio which is in closer agreement with that derived from lidar/sunphotometer measurements in this layer, with still large differences at certain altitudes (the largest relative difference was 46%). We explain these differences by non-uniqueness of the result of the size distribution retrieval, by a lack of information on the mixing state of particles, and the vertical variability of the particle refractive index.

Night-Time Ground Hyperspectral Imaging for Urban-Scale Remote Sensing of Ambient PM. I. Aerosol Optical Thickness Acquisition

“…Moreover, optimally, to obtain the best retrieval the spectral range for analysis should be dynamic and change according to the characteristics of the true environmental (i.e., aerosol) conditions. Many studies in the past 30 years aimed at retrieving bi-or tri-modal atmospheric aerosol PSD from spectral optical thicknesses in the UV-visible and the NIR ranges, acquired by satellite and airborne mounted instruments (Heintzenberg et al 1981;Ferri et al 1995;Wang et al 1996;Franssens 2001;Kocifaj and Horvath 2005;Kuzmanoski et al 2007) or by ground-based radiometers (Dubovik et al 2002;Wang et al 2002). In general, correlations between spectral optical thickness and ground-level fine PM concentrations are highly dependent on site-specific attributes, seasonality, and meteorological conditions such as the relative humidity (RH) and mixing layer height (Schäfer et al 2008).…”

Aerosol closure study by lidar, Sun photometry, and airborne optical counters during DAMOCLES field campaign at El Arenosillo sounding station, Spain

“…In this section we compare lidar ratio values retrieved from elastic lidar signals constrained by Sun‐photometric data (section 3.2) with those calculated from in situ aircraft measurements (section 3.1) in several layers. While the aerosol extinction coefficient is sensitive mainly to the aerosol size distribution and the real part of the refractive index, the lidar ratio also depends on the imaginary part, mixing stage (i.e., the relative contribution of internal and/or external aerosol mixing), and shape of the particles because the backscatter coefficient is sensitive to these properties [ Kuzmanoski et al , 2007]. Therefore this comparison is convenient for testing the validity of the aerosol model in estimating other aerosol optical properties [ Kuzmanoski et al , 2007].…”

Determination of index of refraction and size of supermicrometer particles from light scattering measurements at two angles

“…Certainly questions can be raised about the usefulness of characterizing a complex mixture of atmospheric aerosol, which include non‐spherical, absorbing, multicomponent, externally mixed particles, with a single complex index of refraction. Such a reduction is a significant simplification; however, such simplifications are required for many applications, including retrieving aerosol properties from in situ optical particle measurements [ Guyon et al , 2003; Reidmiller et al , 2006; Kuzmanoski et al , 2007] and active [ Ansmann et al , 2007; Papayannis et al , 2007] and passive [ Remer et al , 2005; Adamopoulos et al , 2007; Mi et al , 2007; Zieger et al , 2007] radiation measurements. Similar simplifications are required for completing radiative transfer calculations [ Kocifaj and Lukac , 1998; Caron et al , 2004] and to assess the role of aerosol in global climate models [ Ghan and Schwartz , 2007].…”