Preprints
https://doi.org/10.5194/acp-2022-328
https://doi.org/10.5194/acp-2022-328
 
25 May 2022
25 May 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

A comprehensive study on hygroscopic behaviour and nitrate depletion of NaNO3 and dicarboxylic acid mixtures: Implication for the influence factors of nitrate depletion

Shuaishuai Ma1, Qiong Li2, and Yunhong Zhang1 Shuaishuai Ma et al.
  • 1The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, PR China
  • 2Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science & Engineering, Institute of Atmospheric Sciences, Fudan University, Shanghai 200433, PR China

Abstract. The nitrate depletion and HNO3 release in internally mixed nitrate and dicarboxylic acids (DCAs) particles have been widely detected in field and laboratory studies. Nevertheless, considerable discrepancies are still present among these measurements, and the influence factors for this acid-displacement reaction have not yet been elucidated. In this work, the hygroscopic growth and chemical composition evolution of mixtures of NaNO3 and DCAs, i.e., oxalic acid (OA), malonic acid (MA), and glutaric acid (GA), were measured using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and vacuum FTIR techniques. The HNO3 release from NaNO3/OA mixtures was observed in both the measurements, owing to the relatively high acidity of OA. At the same time, the NaNO3 phase state was found to act as a key regulator of nitrate depletion. Amorphous NaNO3 solids at relative humidity (RH) < 5 % were inert to liquid OA. With increasing RH, the mixtures experienced three interesting stages of phase changes showing different HNO3 release rates, e.g., at around 15 % RH, the slow HNO3 release was detected by the vacuum IR spectra, potentially indicating the transformation of amorphous solids to semisolid NaNO3; in the second stage (sudden RH increase from ~ 15 % to 61 %), the HNO3 release rate was increased by about an order of magnitude; when NaNO3 deliquescence occurred in the third stage, this displacement reaction proceeded due to more available NO3- ions formation. Compared to OA, MA and GA reacted with nitrate only in vacuum FTIR measurement, while in ATR-FTIR measurement, the mixtures tended to be effloresced completely without nitrate depletion. Further, the influences of ambient pressure, chemical composition, and water activity on HNO3 release rates were estimated via Maxwell steady-state diffusive mass transfer equation. The results showed that weaker acidity of MA and GA as well as relatively lower HNO3 diffusion rate in ambient gas phase mainly contributed to the unobserved nitrate depletion in ATR-FTIR measurement. Our findings reveal that chemical component, phase state, and water activity of particles, as well as HNO3 gas phase diffusion play crucial roles on HNO3 release from nitrate and DCAs mixtures. This work may provide a new perspective on nitrate depletion in the aging processes during transport of atmospheric aerosols.

Shuaishuai Ma et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-328', Anonymous Referee #1, 23 Jun 2022
    • AC2: 'Reply on RC1', Yunhong Zhang, 18 Jul 2022
  • RC2: 'Review of Shuaishuai Ma et al. (acp-2022-328)', Anonymous Referee #2, 02 Jul 2022
    • AC1: 'Reply on RC2', Yunhong Zhang, 18 Jul 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-328', Anonymous Referee #1, 23 Jun 2022
    • AC2: 'Reply on RC1', Yunhong Zhang, 18 Jul 2022
  • RC2: 'Review of Shuaishuai Ma et al. (acp-2022-328)', Anonymous Referee #2, 02 Jul 2022
    • AC1: 'Reply on RC2', Yunhong Zhang, 18 Jul 2022

Shuaishuai Ma et al.

Shuaishuai Ma et al.

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Short summary
The nitrate phase state can play a critical role in determining the occurrence and extent of nitrate depletion in internally mixed NaNO3/DCAs particles, which may be instructive for relevant aerosol reaction systems. Besides, organic acids have a potential to deplete nitrate based on the comprehensive consideration of acidity, particle-phase state, droplet water activity, as well as HNO3 gas phase diffusion.
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