Identifying solid-aqueous-phase transitions in atmospheric aerosols. II. Acidic solutions

Sudhakar Potukuchi, Anthony S. Wexler

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Atmospheric aerosols are often found to be acidic. Predicting the composition of these multi-component aerosols as a function of relative humidity is important in estimating their water content, phase state and acidity. In this work, a computational method that was previously developed and applied to neutral acidity solutions to determine deliquescence relative humidities is extended to acidic solutions. Three sets of acid aerosol compositions are analyzed: H+NH4 +HSO4 -SO4 2-NO3 -, H+NH4 +HSO4 -SO4 2-Cl- and H+NH4NO3 -Cl-. Solubility products are used to determine phase state and water activity at saturation. Activity coefficients are predicted using the recently developed mole-fraction-based thermodynamic model of Clegg and coworkers, along with Pitzer's-molality-based method. Partial dissociation of bisulfate ion, HSO4 - = H+ + SO4 2-, is considered explicitly. For each set of components, water activities at deliquescence are plotted as a function of composition. Trajectories are included that show variation in the composition of the aqueous phase in a multiphase aerosol as a function of relative humidity.

Original languageEnglish (US)
Pages (from-to)3357-3364
Number of pages8
JournalAtmospheric Environment
Issue number22
StatePublished - Nov 1995
Externally publishedYes


  • acid aerosols
  • activity coefficients
  • bisulfate equilibrium
  • Deliquescence
  • Gibbs free energy
  • phase transitions
  • thermodynamic equilibrium
  • water activity

ASJC Scopus subject areas

  • Environmental Science(all)
  • Atmospheric Science
  • Pollution
  • Earth and Planetary Sciences(all)


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