Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols

Abstract

Multi-angle azimuthal measurements of light scattering by individual submicrometre particles have been made with the DAWN-A multi-angle light scattering (MALS) instrument. Variability in azimuthal scattering at a polar angle of 55 • has been used to determine spherical and nonspherical fractions of laboratory-produced and atmospheric aerosols classified at mobility diameters of 0.2-0.8 µm (size parameters of 1.3-5.1). Parameters used for shape fractionation were derived empirically by comparing scattering signatures from crystalline sodium chloride cubes and spherical dioctyl sebacate (DOS) droplets and then applied to test aerosols and atmospheric aerosols sampled at low (3-10%) and high (50-80%) values of relative humidity. DOS and NaCl contrast was great enough to permit their distinction with less than 5% uncertainty for 0.4-0.8 µm, but contrast was observed to decrease as the size parameter approached unity. Crystalline ammonium sulphate test aerosol appeared mildly aspherical, with nonspherical fraction values in the range 15-40%. Nonspherical fractions of atmospheric aerosols measured during the Southeastern Aerosol and Visibility Study (SEAVS), conducted during July and August of 1995, were generally small (<10%), providing confidence in our application of Mie theory for determination of aerosol optical properties. DAWN-A shape data have been compared with aerosol chemistry and hygroscopicity measured during SEAVS, revealing an overall strong correlation of nonspherical fractions to soil dust content and 'less hygroscopic' fractions.

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

“…One disadvantage is that DEHS is a plasticiser so can attack plastic components. Oleic acid and ammonium sulphate have been tested, but the former reacts with oxygen and the latter does not form perfectly spherical aerosol (Dick et al, 1998;Hudson et al, 2007).…”

The density of humic acids and humic like substances (HULIS) from fresh and aged wood burning and pollution aerosol particles

“…Using transmission electron microscopy (TEM) (Dick et al, 1998;Li et al, 2003;Perry et al, 1978), multi-angle light scattering (Dick et al, 1998;Perry et al, 1978) and by measuring particle beam divergence (Huffman et al, 2005) it was shown that by spraying and drying AS solutions, mildly aspherical particles with some significant variability form. Huffman et al (2005) noticed that the lift shape factor of such AS particles increases with particle size ranging from 110 to 320 nm.…”

Just-Noticeable Differences in Atmospheric Haze

“…The SEAVS focused largely on aerosol composition, 5,6 airborne particle size distribution, 7,8 and the role of water in the aerosol. [9][10][11] However, the SEAVS had a number of other aspects, including a study of the perception of color through atmospheric haze.…”