A conceptual framework for mixing structures in individual aerosol particles

Weijun Li, Jiaxing Sun, Liang Xu, Zongbo Shi, Nicole Riemer, Yele Sun, Pingqing Fu, Jianchao Zhang, Yangting Lin, Xinfeng Wang, Longyi Shao, Jianmin Chen, Xiaoye Zhang, Zifa Wang, Wenxing Wang

Research output: Contribution to journalArticlepeer-review


This study investigated the particle size- and age-dependent mixing structures of individual particles in clean and polluted air. Aerosols were classified into eight components: sea salt, mineral dust, fly ash, metal, soot, sulfates, nitrates, and organic matter (OM). Based on our aerosol classification, a particle that consists of two or more aerosol components can be defined as an internally mixed particle. Otherwise, it is considered to be an externally mixed particle. Within the internally mixed particle class, we identified four heterogeneous mixing structures: core-shell, dumbbell, OM coating, and dispersed OM, as well as one homogeneous-like mixing structure. Homogeneous-like mixing mainly occurred in fine particles (<1 µm), while the frequency of heterogeneously mixed particles increased with particle size. Our study demonstrated that particle mixing structures depend on particle size and location and evolve with time. OM-coating and core-shell structures are important indicators for particle aging in air as long as they are distant from specific emission sources. Long-range transported particles tended to have core-shell and OM-coating structures. We found that secondary aerosol components (e.g., sulfates, nitrates, and organics) determined particle mixing structures, because their phases change following particle hydration and dehydration under different relative humidities. Once externally mixed particles are transformed into internally mixed particles, they cannot revert to their former state, except when semivolatile aerosol components are involved. Categorizing mixing structures of individual particles is essential for studying their optical and hygroscopic properties and for tracing the development of their physical or chemical properties over time.

Original languageEnglish (US)
Pages (from-to)784-798
Number of pages15
JournalJournal of Geophysical Research: Atmospheres
Issue number22
StatePublished - Nov 27 2016


  • individual particle
  • morphological mixing state

ASJC Scopus subject areas

  • Atmospheric Science
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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