EGU21-8057, updated on 04 Mar 2021
https://doi.org/10.5194/egusphere-egu21-8057
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Individual Aerosol Droplet pH Measurement via a Ratio-metric Raman Method Using Aerosol Optical Tweezers: Evaluation of Thermodynamic and Activity Models

Meng Li1, Hang Su2, Guangjie Zheng1, Uwe Kuhn2, Guo Li2, Nan Ma3, Ulrich Pöschl2, and Yafang Cheng1
Meng Li et al.
  • 1Minerva Research Group, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 3Institute for Environmental and Climate Research, Jinan University, Guangzhou, China

Measuring pH in individual aerosol droplet is essential for understanding and estimating physicochemical processes within aerosol microenvironments. Recently, aerosol optical tweezers coupling with Raman spectroscopy have been applied to measure the pH of single trapped microdroplets by utilizing conjugate acid-base equilibrium to infer pH shifts. However, such measurements are easily affected by many factors such as variations in detecting volumes and laser intensities, making it hard to directly determine these acid and base concentrations through their respective peak areas. To overcome these problems and accurately measure the concentrations of SO42- and HSO4 within individual NaHSO4 microdroplets, in this study a ratio-metric spectroscopic method is developed based on the peak area ratio of ν(SO42−)/ν(OH) and ν(HSO4)/ν(OH). Combined with the ion balance and ion activity coefficients, droplet pH is determined unambiguously. These experiment results were further used to evaluate the performance of activity models and thermodynamic models associated with aerosol pH, ion concentration and activity coefficient predictions. Pitzer, Simonson, and Clegg (PSC) model provides the best predictions of ion activity coefficients Extended Aerosol Inorganics Model vision IV (E-AIM IV) works well over a wide NaHSO4 concentration range (0.4-8.8 mol/kg), while ACCENT Pitzer model predictions have extremely good agreement with the experiment results in low NaHSO4 concentration condition (≤2.0 mol/kg). By contrast, ISORROPIA II shows relatively poor performance as compared with E-AIM IV.

How to cite: Li, M., Su, H., Zheng, G., Kuhn, U., Li, G., Ma, N., Pöschl, U., and Cheng, Y.: Individual Aerosol Droplet pH Measurement via a Ratio-metric Raman Method Using Aerosol Optical Tweezers: Evaluation of Thermodynamic and Activity Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8057, https://doi.org/10.5194/egusphere-egu21-8057, 2021.