Comparison of size and morphological measurements of coarse mode dust particles from Africa

Abstract

[1] A multitude of sensitivity studies in the literature point to the importance of proper chemical and morphological characterization of particles when the radiative impacts of airborne dusts are modeled. However, the community data set is based on heterogeneous measurement methods relying on varying aerodynamic, chemical, morphological, and optical means. During the Puerto Rico Dust Experiment, size distributions of dust particles from Africa were measured using a variety of aerodynamic, optical, and geometric means. Consistent with the literature, comparisons of these size distributions showed quite dissimilar results. ''Measured'' volume median diameters varied from 2.5 to 9 mm for various geometric, aerodynamic, optical, and optical inversion methods. Aerodynamic systems showed mixed performance. Column integrated size distributions inverted from AERONET Sun/sky radiance data produced somewhat reasonable results in the coarse mode when given proper constraints and taken in the proper context. The largest systematic errors were found in optical particle counters due to insensitivities to particle size in the 4-10 mm region with further complications due to dust particle morphology and index of refraction issues. As these methods can produce quite dissimilar size distributions, considerable errors in calculated radiative properties can occur if incorrectly modeled into dust parameters. None of the methods compared in this study can adequately reproduce the measured mass extinction or mass scattering efficiency of the dust using spherical geometry methods. Given all of the uncertainties in the sizing methods, we promote the use of fundamental and quantifiable descriptors of particles such as mass as a function of aerodynamic diameter.

Optical, physical and chemical characteristics of Australian continental aerosols: results from a field experiment

“…The autumn and winter distributions show lower total aerosol content, with the coarse mode again dominating. While some inversions may be biased as a consequence of the low AOD values, especially in winter, these distributions are consistent with those from Africa studied by Reid et al (2003), and from Arabia by Eck et al (2008). Figure 6b shows the volume size distributions for selected days during spring 2007, and we see that the coarse mode peak shifts from day to day.…”

In situ measurements of desert dust particles above the western Mediterranean Sea with the balloon-borne Light Optical Aerosol Counter/sizer (LOAC) during the ChArMEx campaign of summer 2013

“…12). Reid et al (2003b) discuss that the FSSP measurement principle tends to produce some oversizing of coarse particles and also shows particle concentrations as high as twice those measured by a passive cavity aerosol spectrometer probe (PCASP) in their overlapping particle diameter range (1.5-3 µm). This could explain such a shift in our data set.…”

On realistic size equivalence and shape of spheroidal Saharan mineral dust particles applied in solar and thermal radiative transfer calculations

“…Recent studies report that losses of coarse mode particles may occur (Reid et al, 2003;Linke et al, 2006;Johnson et al, 2008a;McConnell et al, 2008;Chen et al, 2011). While Schmid et al (2000) performed cut-off corrections, McConnell et al (2010) refer the optical properties, based on size-limited particle information, to the observed accumulation mode of the entire dust ensemble.…”

“…Efforts have been made to measure them . Nevertheless each measurement is accompanied by certain inaccuracies (Reid et al, 2003) and, unfortunately, it is difficult to measure large particles, since they, e.g., may be picked by the inlet system (cut-off problem). Thus, we wish to study the effect of maximum particle size in a dust size distribution on optical properties and forcing in order to simulate the cut-off problem.…”