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


Principal Investigator

Christopher Cappa — University of California - Davis


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.

Related Publications

Atkinson D, M Pekour, D Chand, J Radney, K Kolesar, Q Zhang, A Setyan, NT O'Neill, and C Cappa. 2018. "Using spectral methods to obtain particle size information from optical data: applications to measurements from CARES 2010." Atmospheric Chemistry and Physics, 18(8), 10.5194/acp-18-5499-2018.

Cappa CD, KR Kolesar, X Zhang, DB Atkinson, MS Pekour, RA Zaveri, A Zelenyuk, and Q Zhang. 2016. "Understanding the optical properties of ambient sub- and supermicron particulate matter: results from the CARES 2010 field study in northern California." Atmospheric Chemistry and Physics, 16(10), 10.5194/acp-16-6511-2016.

Liu S, AC Aiken, K Gorkowski, MK Dubey, CD Cappa, LR Williams, SC Herndon, C Massoli, EC Fortner, PS Chhabra, WA Brooks, TB Onasch, JT Jayne, DR Worsnop, S China, N Sharma, C Mazzoleni, L Xu, NL Ng, D Liu, JD Allan, JD Lee, ZL Fleming, C Mohr, P Zotter, S Szidat, and AH Prevot. 2015. "Enhanced light absorption by mixed source black and brown carbon particles in UK winter." Nature Communications, 6, 8435, 10.1038/ncomms9435.

Atkinson DB, JG Radney, J Lum, KR Kolesar, DJ Cziczo, MS Pekour, Q Zhang, A Setyan, A Zelenyuk, and CD Cappa. 2015. "Aerosol optical hygroscopicity measurements during the 2010 CARES campaign." Atmospheric Chemistry and Physics, 15(8), 10.5194/acp-15-4045-2015.