Characterizing the Impact of Water Uptake on Light Absorption by Aerosol Particles

Abstract

Absorbing aerosols have an important impact on the global radiation budget. The composition and properties of absorbing aerosols can vary substantially throughout the atmosphere, depending on the particle source and the influence of chemical aging. Uncertainties associated with the radiative effects of absorbing aerosols remain substantial. A key contributor to this uncertainty is understanding the extent to which water uptake alters absorption by absorbing particles and how this depends on particle composition. We propose to use new and existing experimental tools to systematically characterize the relationship(s) between absorbing aerosol chemical and physical characteristics, relative humidity, and mixing of absorbing aerosols with other aerosol components through a combination of laboratory and field measurements. We will develop fundamental understanding through laboratory experiments that will enable interpretation of field observations at DOE ARM sites and facilitate process-based improvements in the simulation of absorption by carbonaceous aerosols in climate models.

In the laboratory experiments we will consider a variety of different absorbing particle types, including flame-derived (black carbon), chemically-generated (brown carbon), and commercially available surrogate absorbing particles. By examining a range of absorbing aerosol types we will develop insight into how the chemical and physical properties of absorbing particles (e.g. whether they are refractory or soluble) impact the influence of water uptake on absorption. These absorbing particles will also be mixed—both internally and externally—with compounds having a wide range of hygroscopic properties to establish how the impact of water uptake on absorption will vary with photochemical processing. These laboratory observations will be compared with commonly used theoretical models, and robust parameterizations will be developed to facilitate improved representation of absorption by absorbing particles in regional and global climate models. Given the inherent complexity of and substantial variability in the mixing state of absorbing aerosols in the atmosphere, our systematic laboratory experiments on mixed-component absorbing aerosol systems of varying complexity will provide a foundation for robust interpretation of future ambient observations.

Overall, our study will contribute to the mission of the Atmospheric System Research program by quantifying how interactions between aerosols and radiation depend on relative humidity. Through this, our work will improve understanding and model representation of aerosol processes as they affect the Earth’s radiation budget.