Light scattering Q‐space analysis of irregularly shaped particles

Abstract

AbstractWe report Q‐space analysis of light scattering phase function data for irregularly shaped dust particles and of theoretical model output to describe them. This analysis involves plotting the scattered intensity versus the magnitude of the scattering wave vector q = (4π/λ)sin(θ/2), where λ is the optical wavelength and θ is the scattering angle, on a double‐logarithmic plot. In q‐space all the particle shapes studied display a scattering pattern which includes a q‐independent forward scattering regime; a crossover, Guinier regime when q is near the inverse size; a power law regime; and an enhanced backscattering regime. Power law exponents show a quasi‐universal functionality with the internal coupling parameter ρ′. The absolute value of the exponents start from 4 when ρ′ < 1, the diffraction limit, and decreases as ρ′ increases until a constant 1.75 ± 0.25 when ρ′ ≳ 10. The diffraction limit exponent implies that despite their irregular structures, all the particles studied have mass and surface scaling dimensions of Dm = 3 and Ds = 2, respectively. This is different from fractal aggregates that have a power law equal to the fractal dimension Df because Df = Dm = Ds < 3. Spheres have Dm = 3 and Ds = 2 but do not show a single power law nor the same functionality with ρ′. The results presented here imply that Q‐space analysis can differentiate between spheres and these two types of irregularly shaped particles. Furthermore, they are applicable to analysis of the contribution of aerosol radiative forcing to climate change and of aerosol remote sensing data.