Computer-controlled Raman microspectroscopy (CC-Raman): A method for the rapid characterization of individual atmospheric aerosol particles

ABSTRACT

The ability of an atmospheric aerosol particle to impact climate by acting as a cloud condensation nucleus (CCN) or an ice nucleus (IN), as well as scatter and absorb solar radiation is determined by its physicochemical properties at the single particle level, specifically size, morphology, and chemical composition. The identification of the secondary species present in individual aerosol particles is important as aging, which leads to the formation of these species, can modify the climate relevant behavior of particles. Raman microspectroscopy has a great deal of promise for identifying secondary species and their mixing with primary components, as it can provide detailed information on functional groups present, morphology, and internal structure. However, as with many other detailed spectroscopic techniques, manual analysis by Raman microspectroscopy can be slow, limiting single particle statistics and the number of samples that can be analyzed. Herein, the application of computer-controlled Raman (CC-Raman) for detailed physicochemical analysis that increases throughput and minimizes user bias is described. CC-Raman applies automated mapping to increase analysis speed allowing for up to 100 particles to be analyzed in an hour. CC-Raman is applied to both laboratory and ambient samples to demonstrate its utility for the analysis of both primary and, most importantly, secondary components (sulfate, nitrate, ammonium, and organic material). Reproducibility and precision are compared to computer controlled-scanning electron microscopy (CCSEM). The greater sample throughput shows the potential for CC-Raman to improve particle statistics and advance our understanding of aerosol particle composition and mixing state, and, thus, climate-relevant properties.

© 2017 American Association for Aerosol Research

EDITOR:

• Paul Ziemann

Acknowledgments and funding

University of Michigan startup funds supported this project. The Michigan Center for Materials Characterization (MC²) is acknowledged for assistance with CCSEM. Funding for SOAS sampling was provided by the Environmental Protection Agency (EPA). Professors Paul Shepson, Steve Bertman, Kerri Pratt, Ann Marie Carlton, as well as Manelisi Nhliziyo are thanked for assistance with SOAS sampling. The SOAS CCSEM analysis was performed at the Environmental Molecular Sciences Laboratory (EMSL), with assistance from Professor Alex Laskin and Dr. Bingbing Wang, a Department of Energy (DOE) national user facility sponsored by the Office of Biological and Environmental Research at Pacific Northwest National Laboratory (PNNL). PNNL is operated for DOE by Battelle Memorial Institute under Contract No. DE-AC06-76RL0 1830. The University of Michigan Graduate School and Office of the Provost provided travel funds to PNNL.