Size dependence of in situ pH in submicron atmospheric particles in Hong Kong

Xiaohong Yao, Tsz Yan Ling, Ming Fang, Chak K. Chan

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48 Scopus citations


Some studies have reported that small submicron atmospheric particles are more acidic than large submicron particles; other studies demonstrated a reversed trend. In this study, the size dependence of in situ pH in submicron particles in Hong Kong was investigated. The equivalent ratios of [NH4+]measured to [SO42-]measured in submicron particles were found to be generally less than unity and size dependent, suggesting the possibility of incomplete gas-aerosol equilibrium. The Aerosol Inorganic Model-II (AIM-II) model using measured ionic compositions with the gas-aerosol partitioning disabled was used to estimate the in situ pH in different sized particles. The estimated in situ pH of different sized submicron atmospheric particles was between -2.5 and 1.5 and it generally decreases with increasing submicron particle size. At such low in situ pH, the estimated HSO4- equivalent concentrations were 3.2 times (on average) of those of H+ in different sized particles. The trends of the size dependence of the [NH4+]measured to [SO42-]measured ratio and pH under different regimes of relative humidity are discussed. © 2006 Elsevier Ltd. All rights reserved.
Original languageEnglish (US)
Pages (from-to)382-393
Number of pages12
JournalAtmospheric Environment
Issue number2
StatePublished - Jan 1 2007
Externally publishedYes

Bibliographical note

Generated from Scopus record by KAUST IRTS on 2023-07-06

ASJC Scopus subject areas

  • Environmental Science(all)
  • Atmospheric Science


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