T-matrix modeling of linear depolarization by morphologically complex soot and soot-containing aerosols

Abstract

a b s t r a c tWe use state-of-the-art public-domain Fortran codes based on the T-matrix method to calculate orientation and ensemble averaged scattering matrix elements for a variety of morphologically complex black carbon (BC) and BC-containing aerosol particles, with a special emphasis on the linear depolarization ratio (LDR). We explain theoretically the quasi-Rayleigh LDR peak at side-scattering angles typical of low-density soot fractals and conclude that the measurement of this feature enables one to evaluate the compactness state of BC clusters and trace the evolution of low-density fluffy fractals into densely packed aggregates. We show that small backscattering LDRs measured with groundbased, airborne, and spaceborne lidars for fresh smoke generally agree with the values predicted theoretically for fluffy BC fractals and densely packed near-spheroidal BC aggregates. To reproduce higher lidar LDRs observed for aged smoke, one needs alternative particle models such as shape mixtures of BC spheroids or cylinders.Published by Elsevier Ltd.

Use of the CALIOP vertical feature mask for evaluating global aerosol models

“…Sensitivity analyses we performed (not shown here) suggest that our simulated dust depolarization ratio is not strongly sensitive to any errors we have in the simulated dust particle size, as suggested by Freudenthaler et al (2009), so we speculate here that we are fundamentally limited either because of our assumption that dust particles are ellipsoidal or because of our assumption that they are homogeneous in composition. Imaging of dust particles shows that neither assumption is true (e.g., Buseck and Posfai, 1999), and there is at least theoretical evidence that inclusion of heterogeneity within particles can lead to higher depolarization ratios (Mishchenko et al, 2013). In an attempt to match observed depolarization ratios (∼ 0.31), we therefore increase our simulated dust depolarization ratios by 30 % for our analysis.…”

The Carbon Aerosol / Particles Nucleation with a Lidar: Numerical Simulations and Field Studies

“…Starting from an observed NPF-event promoted by desert dust particles [10], we numerically simulated the corresponding lidar particles backscattering coefficient βNPF, by applying the Mie theory to freshly nucleated sulfuric acid particles and the T-matrix numerical code [9] for non-spherical desert dust particles. We hence retrieved the optical requirement for detecting such a nucleation event (NPF-event) promoted by desert dust particles, for which the lidar backscattering coefficient βNPF is equal to 0.7 Mm -…”

“…In the literature, the terminology related to the carbon aerosol involves soot particles, carbonaceous particles, and biomass burning, as well as secondary organic aerosols, to quote only a few. The carbon aerosol light absorbing properties have been addressed through laboratory measurements on soot particles [8] and accurate numerical simulations [9]. While determining the spatial and temporal behavior of the carbon aerosol is essential for developing carbon reduction emission strategies, in this contribution, we perform a field experiment, supported by a numerical simulation, based on coupling the lidar and LII-techniques, to retrieve a range-resolved profile of LII-thermal radiation emitted by the carbon of an urban atmosphere over several hundred meters.…”

Short wave radiative impact of liquid-liquid phase separation in Brown Carbon aerosols

“…In particular, the T-matrix approach of Mackowski andMishchenko (1996) and solves the problem of obtaining random-orientation properties of clusters of spheres in a numerically efficient manner. In our context, it has been applied in recent years for computing scattering and absorption of 20 morphologically complex soot containing aerosol (e.g., Mishchenko et al, 2013, Cheng et al, 2014. Here, we use the Multiple Sphere T Matrix (MSTM) version 3.0 (Mackowski, 2013, http://eng.auburn.edu/users/dmckwski/scatcodes/) to compute fixed and random oriented scattering and absorption cross sections as well as the asymmetry parameter for eccentric core shell liquid-liquid phase separated aerosol with a molecular absorber in the organic phase.…”