4.8 Article

Images reveal that atmospheric particles can undergo liquid-liquid phase separations

Publisher

NATL ACAD SCIENCES
DOI: 10.1073/pnas.1206414109

Keywords

chemistry; physical state; secondary organic aerosol; ambient aerosol; atmospheric chemistry

Funding

  1. National Sciences and Engineering Research Council of Canada
  2. US National Science Foundation [0925467, 0802237, 0909227]
  3. Office of Science (BER) of the US Department of Energy
  4. Pacific Northwest National Laboratory Aerosol Climate Initiative
  5. Directorate For Geosciences
  6. Div Atmospheric & Geospace Sciences [0802237] Funding Source: National Science Foundation
  7. Div Atmospheric & Geospace Sciences
  8. Directorate For Geosciences [0925467] Funding Source: National Science Foundation
  9. Division Of Chemistry
  10. Direct For Mathematical & Physical Scien [909227] Funding Source: National Science Foundation

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A large fraction of submicron atmospheric aerosol particles contains both organic material and inorganic salts. As the relative humidity cycles in the atmosphere and the water content of the particles correspondingly changes, these mixed particles can undergo a range of phase transitions, possibly including liquid-liquid phase separation. If liquid-liquid phase separation occurs, the gas-particle partitioning of atmospheric semivolatile organic compounds, the scattering and absorption of solar radiation, and the reactive uptake of gas species on atmospheric particles may be affected, with important implications for climate predictions. The actual occurrence of liquid-liquid phase separation within individual atmospheric particles has been considered uncertain, in large part because of the absence of observations for real-world samples. Here, using optical and fluorescence microscopy, we present images that show the coexistence of two noncrystalline phases for real-world samples collected on multiple days in Atlanta, GA as well as for laboratory-generated samples under simulated atmospheric conditions. These results reveal that atmospheric particles can undergo liquid-liquid phase separations. To explore the implications of these findings, we carried out simulations of the Atlanta urban environment and found that liquid-liquid phase separation can result in increased concentrations of gas-phase NO3 and N2O5 due to decreased particle uptake of N2O5.

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