Ph.D. Defense: Daniel Orozco

Tittle: Aerosols, light, and water: Measurements of aerosol optical properties at different relative humidities.

Abstract: The Earth’s atmosphere is composed of a large number of different gases as well as tiny suspended particles, both in solid and liquid state. These tiny particles, called atmospheric aerosols, have an  immense impact on our health and on our global climate. In ambient conditions, aerosol particles experience hygroscopic growth due to the influence of relative humidity (RH); therefore, humid particles scatter more light than when the particles are dry. The quantitative knowledge of the RH effect and its influence on the light scattering is important to verify assumptions used in remote sensing techniques and for the improvement of climate models. In this work, we use a novel instrument called PI-NEPH (Polarized Imaging Nephelometer), designed and built at UMBC, to measure the first two elements of the scattering matrix for laboratory-generated and ambient aerosol particles. The measurements were performed at different RH levels in order to observe the changes in the optical properties when the particles are dry and after they absorb water. The results showed significant changes in the optical properties due to the hygroscopic growth. These changes were evaluated through classic thermodynamic equilibrium theory producing comparable results between measurements and simulations made with Mie formalism.