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<p>Hygroscopicity of bromine salt influences the formation of cloud condensation activity (CCN) and CCN number concentrations, thereby affecting cloud formation. However, the current study on the hygroscopicity of bromine-containing aerosols has not been fully understood. In this study, we focus on the hygroscopicity and CCN of bromine salt such as sodium bromide (NaBr) and ammonium bromide (NH<sub>4</sub>Br) using a hygroscopic tandem differential mobility analyzer (H-TDMA) and a cloud condensation nuclei counter (CCNC) at 24 ± 1 ℃. The hygroscopic behavior of bromine salts differs from humic acid’s hygroscopic growth, with deliquescence relative humidity (DRH) and different CCN for NaBr and NH<sub>4</sub>Br aerosol particles. The hygroscopic parameter <i>κ</i> for NaBr was determined to be 0.89, larger than the <i>κ</i> value of 0.77 measured for NH<sub>4</sub>Br. NaBr deliquesced at 45%, compared with a DRH of 75% for NH<sub>4</sub>Br aerosols. However, 100&#xa0;nm humic acid aerosols show no obvious DRH. The measurements are accompanied by RH-dependent thermodynamic equilibrium calculations using the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model. There are several effects of humic acid on the hygroscopicity and CCN activity of mixtures containing NaBr and NH<sub>4</sub>Br in relation to the different mass fractions of organic compounds: (1) a shift of DRH of NaBr to higher RH (1.5 to 3.7%) with increasing mass fraction from 25 to 50 wt% of humid acid in the mixture. No DRH was observed in the bromine-containing aerosols with an HA mass fraction of 75 wt%. (2) the usage of Zdanovskii–Stokes–Robinson (ZSR) relation leads to agreement with measured diameter growth factors of aerosol particles containing humic acid and bromine salt. (3) the <i>κ</i> differences between sub- and supersaturated conditions ranged from − 0.28 to 0.14 for 1:1 NaBr/HA, 1:3 NaBr/HA, and all NH<sub>4</sub>Br/HA mixture aerosols, falling within experimental uncertainty. Therefore, it provides insights into the hygroscopicity and cloud condensation nuclei of bromine salts and their interactions with humic acid under sub- and supersaturated conditions, which are crucial for comprehending the atmospheric life processes and impacts of bromine salts.</p>

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Hygroscopicity and Cloud Condensation Nucleation Activity of Bromine Salts

  • 期刊论文

  • 发表日期：

    2026年1月22日

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  • Jiali Zhong,
  • Ting Lei,
  • Chao Peng,
  • Wenjun Gu,
  • Nan Ma,
  • Zhe Wang,
  • Maofa Ge,
  • Weigang Wang

摘要

Hygroscopicity of bromine salt influences the formation of cloud condensation activity (CCN) and CCN number concentrations, thereby affecting cloud formation. However, the current study on the hygroscopicity of bromine-containing aerosols has not been fully understood. In this study, we focus on the hygroscopicity and CCN of bromine salt such as sodium bromide (NaBr) and ammonium bromide (NH4Br) using a hygroscopic tandem differential mobility analyzer (H-TDMA) and a cloud condensation nuclei counter (CCNC) at 24 ± 1 ℃. The hygroscopic behavior of bromine salts differs from humic acid’s hygroscopic growth, with deliquescence relative humidity (DRH) and different CCN for NaBr and NH4Br aerosol particles. The hygroscopic parameter κ for NaBr was determined to be 0.89, larger than the κ value of 0.77 measured for NH4Br. NaBr deliquesced at 45%, compared with a DRH of 75% for NH4Br aerosols. However, 100 nm humic acid aerosols show no obvious DRH. The measurements are accompanied by RH-dependent thermodynamic equilibrium calculations using the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model. There are several effects of humic acid on the hygroscopicity and CCN activity of mixtures containing NaBr and NH4Br in relation to the different mass fractions of organic compounds: (1) a shift of DRH of NaBr to higher RH (1.5 to 3.7%) with increasing mass fraction from 25 to 50 wt% of humid acid in the mixture. No DRH was observed in the bromine-containing aerosols with an HA mass fraction of 75 wt%. (2) the usage of Zdanovskii–Stokes–Robinson (ZSR) relation leads to agreement with measured diameter growth factors of aerosol particles containing humic acid and bromine salt. (3) the κ differences between sub- and supersaturated conditions ranged from − 0.28 to 0.14 for 1:1 NaBr/HA, 1:3 NaBr/HA, and all NH4Br/HA mixture aerosols, falling within experimental uncertainty. Therefore, it provides insights into the hygroscopicity and cloud condensation nuclei of bromine salts and their interactions with humic acid under sub- and supersaturated conditions, which are crucial for comprehending the atmospheric life processes and impacts of bromine salts.