Preprints
https://doi.org/10.5194/acp-2021-55
https://doi.org/10.5194/acp-2021-55

  12 Apr 2021

12 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Impact of non-ideality on reconstructing spatial and temporal variations of aerosol acidity with multiphase buffer theory

Guangjie Zheng1, Hang Su2, Siwen Wang2, Andrea Pozzer3, and Yafang Cheng1 Guangjie Zheng et al.
  • 1Minerva Research Group, Max Planck Institute for Chemistry, Mainz 55128, Germany
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
  • 3Air Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany

Abstract. Aerosol acidity is a key parameter in atmospheric aqueous chemistry and strongly influence the interactions of air pollutants and ecosystem. The recently proposed multiphase buffer theory provides a framework to reconstruct long-term trends and spatial variations of aerosol pH based on the effective acid dissociation constant of ammonia (Ka,NH3*). However, non-ideality in aerosol droplets is a major challenge limiting its broad applications. Here, we introduced a non-ideality correction factor (cni) and investigated its governing factors. We found that besides relative humidity (RH) and temperature, cni is mainly determined by the molar fraction of NO3 in aqueous-phase anions, due to different NH4+ activity coefficients between (NH4)2SO4− and NH4NO3-dominated aerosols. A parameterization method is thus proposed to estimate cni at given RH, temperature and NO3 fraction, and is validated against long-term observations and global simulations. In the ammonia-buffered regime, with cni correction the buffer theory can well reproduce the Ka,NH3* predicted by comprehensive thermodynamic models, with root-mean-square deviation ~0.1 and correlation coefficient ~1. Note that, while cni is needed to predict Ka,NH3* levels, it is usually not the dominant contributor to its variations, as ~90 % of the temporal or spatial variations in Ka,NH3* is due to variations in aerosol water and temperature.

Guangjie Zheng et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-55', Anonymous Referee #1, 10 May 2021 reply

Guangjie Zheng et al.

Guangjie Zheng et al.

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Short summary
The recently proposed multiphase buffer theory provides a framework to reconstruct long-term trends and spatial variations of aerosol pH, while non-ideality is a major limitation for its broad applications. Here we proposed a parameterization method to estimate the impact of non-ideality, and validated it against long-term observations and global simulations. With this method, the multiphase buffer theory can well reproduce aerosol pH variations estimated by comprehensive thermodynamic models.
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