AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Assessing Aerosol Mixing State through Single Particle Mass Spectrometry and Particle-Resolved Modeling
NICOLE RIEMER, Swarnali Sanyal, Robert Healy, Greg J. Evans, John Wenger, University of Illinois at Urbana-Champaign
Abstract Number: 347 Working Group: Urban Aerosols
Abstract The mixing state of the aerosol population is the distribution of chemical compounds across the particle population. Recent field observations using single-particle measurement techniques have revealed that the mixing states of ambient aerosol populations are complex. Even freshly emitted particles can have complex compositions by the time they enter the atmosphere, and the initial particle composition is further modified in the atmosphere as a result of aging processes including coagulation, condensation of secondary aerosol species, and heterogeneous reactions. Considering this, it becomes clear that the frequently used terms “external mixture” and “internal mixture” are rarely sufficient to characterize the mixing state of ambient aerosol populations.
In this work, a newly developed framework for quantifying aerosol mixing state based on information-theoretic entropy is applied for the first time to single particle mass spectrometry field data combined with process modeling using the particle-resolved model PartMC-MOSAIC. Single-particle composition estimates for black carbon, organic aerosol and inorganic ions are derived for data collected at an urban site in Paris, France. The composition of each particle is described in terms of its species “diversity” and compared to the composition of the bulk aerosol to derive a quantitative mixing state index. This index is a single parameter representation of how internally or externally mixed a particle population is at a given time, and describes a continuum, with values of 0% and 100% representing full external and internal mixing, respectively. The mixing state index of ambient aerosol in Paris is 59% on average, but changes as a function of time of day and air mass origin between 40% and 70%. This approach represents a new means by which to compare and contrast aerosol chemical mixing state in various environments globally, and the process modeling elucidates the mechanisms of aging in the particular environment.