Spectral Characterization of Atmospheric Dust from the IR to the UV: A Combined Laboratory and Modeling Study of Composition, Size, and Shape Effects on Dust Optical Properties

University Of Iowa, Iowa City IA

Investigators

Abstract

Mineral dust aerosol plays a critical role in the atmosphere. Dust affects the Earth's radiation balance by direct absorption and scattering of light across the spectrum from infrared (IR) to ultraviolet (UV). Atmospheric dust particles also serve as sites for cloud nucleation indirectly affecting albedo, and as reactive surfaces for tropospheric reactions altering the chemical balance for important gas phase species such as SO2. Correctly modeling the effects of dust in weather, climate, and air quality requires accurate information about dust loading and composition, size and shape (CSS) distributions, as well as proper treatment of dust optical (scattering and absorption) properties. Dust loading and CSS distributions can be obtained by optical remote sensing. However, remote sensing dust retrievals also depend critically on an accurate treatment of aerosol optical properties. Thus, uncertainties in dust optical properties can lead to errors in estimated dust loading, and CSS distributions with deleterious consequences for weather and air quality forecasts and climate modeling. Intellectual merit. We will investigate dust optical properties across the IR-UV spectrum through laboratory measurements and modeling analyses. The study will focus on authentic dust samples. Aerosol extinction and light scattering properties will be analyzed by measurements of particle CSS distributions through real-time in situ single particle time-of-flight mass spectrometry and particle sizing, and various ex situ methodologies. Since the particle CSS distributions will be measured simultaneously with the optical properties, detailed comparisons with theoretical simulations will be possible, with few (or no) adjustable parameters. The main goals of this work are to establish methods for using spectroscopic and polarimetric measurements to infer mineral dust aerosol CSS distributions, and to explore how these distributions may be altered by atmospheric aging. The qualitative insight and quantitative data provided by this work can be incorporated into remote-sensing retrieval algorithms, improving the reliability of aerosol radiative transfer models for dust retrievals and climate forcing calculations, and thus transforming our understanding of the impact of dust on atmospheric chemistry, dynamics, and climate. Broader impacts. The proposed activities offer tremendous opportunities for post-doctoral fellows and students to develop as independent scientists. This research includes aspects of experimental aerosol science, light scattering, spectroscopy, and reaction kinetics studies, combined with an extensive theoretical modeling program. Students participate in all facets of the work, presenting their results at seminars and conferences. The PIs, through a long standing collaboration, have successfully mentored students and post-doctors at all levels in preparation for professional careers in academia and industry. More than half of the students involved in the research program have been women or from underrepresented minorities. The program also maintains active collaborations with faculty from small colleges in state Iowa, enhancing their research and teaching.