Atmos. Chem. Phys. Discuss., 14, 3973-4005, 2014
www.atmos-chem-phys-discuss.net/14/3973/2014/
doi:10.5194/acpd-14-3973-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Single particle diversity and mixing state measurements
R. M. Healy1,2, N. Riemer3, J. C. Wenger2, M. Murphy1, M. West4, L. Poulain5, A. Wiedensohler5, I. P. O'Connor2, E. McGillicuddy2, J. R. Sodeau2, and G. J. Evans1
1Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, 200 College Street, Toronto, Ontario, Canada
2Department of Chemistry and Environmental Research Institute, University College Cork, Ireland
3University of Illinois at Urbana-Champaign, Department of Atmospheric Sciences, USA
4University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering, USA
5Leibniz Institute for Tropospheric Research, Leipzig, Germany

Abstract. A newly developed framework for quantifying aerosol particle diversity and mixing state based on information-theoretic entropy is applied for the first time to single particle mass spectrometry field data. Single particle mass fraction estimates for black carbon, organic aerosol, ammonium, nitrate and sulphate, derived using single particle mass spectrometer, aerosol mass spectrometer and multi-angle absorption photometer measurements are used to calculate single particle species diversity (Di). The average single particle species diversity (Dα) is then related to the species diversity of the bulk population (Dγ) to derive a mixing state index value (χ) at hourly resolution. The mixing state index is a single parameter representation of how internally/externally mixed a particle population is at a given time. The index describes a continuum, with values of 0% and 100% representing fully external and internal mixing, respectively. This framework was applied to data collected as part of the MEGAPOLI winter campaign in Paris, France 2010. Di values are low (∼2) for fresh traffic and woodburning particles that contain high mass fractions of black carbon and organic aerosol but low mass fractions of inorganic ions. Conversely, Di values are higher (∼4) for aged carbonaceous particles containing similar mass fractions of black carbon, organic aerosol, ammonium, nitrate and sulphate. Aerosol in Paris is estimated to be 59% internally mixed in the size range 150–1067 nm, and mixing state is dependent both upon time of day and air mass origin. Daytime primary emissions associated with vehicular traffic and woodburning result in low χ values, while enhanced condensation of ammonium nitrate on existing particles at night leads to higher χ values. Advection of particles from continental Europe containing ammonium, nitrate and sulphate leads to increases in Dα, Dγ and χ. The mixing state index represents a useful metric by which to compare and contrast ambient particle mixing state at other locations globally.

Citation: Healy, R. M., Riemer, N., Wenger, J. C., Murphy, M., West, M., Poulain, L., Wiedensohler, A., O'Connor, I. P., McGillicuddy, E., Sodeau, J. R., and Evans, G. J.: Single particle diversity and mixing state measurements, Atmos. Chem. Phys. Discuss., 14, 3973-4005, doi:10.5194/acpd-14-3973-2014, 2014.
 
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