A novel laboratory methodology to evaluate the particle extinction-to-backscatter ratio or particle lidar ratio of aerosols

While atmospheric particles are ubiquitous in nature and contribute to the Earth’s radiative budget, their backscattering and extinction remain insufficiently quantified due to their complexity in size, shape and chemical composition. In this paper, a novel laboratory methodology is proposed to evaluate the particle extinction-to-backscatter ratio or lidar ratio of aerosols. This methodology, called LR-lab, is based on a robust light backscatter experiment at 180.0° angle, enhanced with a cavity ring down experiment to evaluate the particle extinction. No assumption is required on the particle size, shape, nor complex refractive index. Our methodology is validated on homogeneous spherical water droplets, which follow the analytical Mie theory, for different water droplets sizes and number concentrations. The particle extinction-to-backscatter ratio of mineral dust, a heterogeneous mixture of non-spherical particles, is then evaluated at 532 nm wavelength in laboratory. The dust lidar ratio is found to be equal to (47 ± 2) sr while the dust depolarization ratio is equal to (33.6 ± 0.4) %. By proposing a combined laboratory evaluation of the particle lidar and depolarization ratios, we believe our methodology can meet the growing need for lidar-based aerosol typing and for validation of light scattering numerical models on complex-shaped particles.