Portable device to determine particle asymmetry parameter.

Yuli W Heinson,Christopher M Sorensen,Rajan K Chakrabarty

doi:10.1364/oe.27.010152

Abstract

Accurate characterization of the asymmetry parameter g is of crucial importance for radiative transfer calculations. Here, we present a portable light scattering (PLS) device designed for in situ, real-time, and contact-free measurements of the particle phase function. The integration time is 20ms for each measurement. Using this device, we measured g values for laboratory-generated brown (organic) carbon aerosol and soot, and commercially available Arizona Road Dust. For the three types of aerosol, the g values were 0.664 ± 0.002, 0.506 ± 0.004, and 0.701 ± 0.020, respectively. The smallest angle our PLS device approaches is 0.7°, which is an order of magnitude smaller than that of commercial nephelometers, thus facilitating more accurate determination of g.

Highlights

The asymmetry parameter g is the weighted average of the normalized scattered intensity with the cosine of the scattering angle and describes the directionality of the scattered light from particles
Accurate values of g are essential in many radiative transfer and climate models to assess aerosol radiative effects of the climate [1, 2]
Based on the size distribution of water droplets generated at 137.9 kPa (20 psi) [17] we calculated the theoretical scattered intensity to compare with the experimental data

Summary

Introduction

The asymmetry parameter g is the weighted average of the normalized scattered intensity with the cosine of the scattering angle and describes the directionality of the scattered light from particles. It can be considered as the ratio of the light scattered in the forward direction over that of the backward direction. By assuming S11 remains constant at θ≤0.7 ̊, which is the case for particles with radius of gyration Rg < 6.9 μm, we determine the asymmetry parameter g by adapting the concept of Eq (1) by integrating S11, over angle range 0 ̊ to 162 ̊ for in situ, real-time, and contact-free measurements

Instrument design

System test

Carbonaceous and non-carbonaceous aerosol particles characterization

Findings

Conclusion