Ambient aerosol particles can undergo dynamic mixing processes as they coagulate with particles from other air masses and emission sources. Therefore, aerosols exist in a spectrum, from externally mixed to internally mixed. The mixing state of aerosols can affect their ability to uptake water (hygroscopicity) and their cloud condensation nuclei (CCN) activity, modifying their contribution to the planet’s total radiative budget. However, current water-uptake measurement methods may not be able to capture the complex mixing state. In this research, the dynamic mixing process was simulated by the particle-resolved aerosol model PartMC and also created by experiments in a laminar flow mixing tube. The mixing evolution of ammonium sulfate and sucrose binary mixtures were observed along with the changes in their water uptake properties expressed as the single hygroscopicity parameter, κ. The use of a mixing simulation in conjunction with experiments allow for better identification of the particle mixing state and the particle water uptake and show that no one kappa value can capture the complexity of mixing across the mixed particle size distribution. In other words, the PartMC simulations can be used as a guiding tool to interpret a system’s mixing state based on its experimental droplet activation spectra. This work demonstrates the importance of the integration and use of mixing models to aid in mixing state determination and hygroscopicity measurements of mixed systems.
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Effects of Mixing State on Water-Uptake Properties of Ammonium Sulfate – Organic Mixtures
Aerosol particles in the atmosphere have the ability to uptake water and form droplets. The droplets formed can interact with solar radiation (indirect effect of aerosols) and influence the net radiative forcing. However, the magnitude of change in radiative forcing due to the indirect effect of aerosols remains uncertain due to the high variance in aerosol composition and mixing states, both spatial and temporally. As such, there is a need to measure the water-uptake of different aerosol particle groups under controlled conditions to gain insight into the water-uptake of complex ambient systems. In this work, the water-uptake (hygroscopicity) of internally and externally mixed ammonium sulfate – organic binary mixtures were directly measured via three methods and compared to droplet growth prediction models. We found that subsaturated water-uptake of ammonium sulfate-organic mixtures agreed with their supersaturated hygroscopicity, and mixing state information was able to be retrieved at both humidity regimes. In addition, we found that solubility-adjusted models may not be able to capture the water-uptake of viscous particles, and for soluble organic aerosol particles, bulk solubility may not be comparable to their solubility in a droplet. This work highlights the importance of using multiple complementary water-uptake measurement instruments to get a clearer picture of mixed aerosol particle hygroscopicity, especially for increasingly complex systems.
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- NSF-PAR ID:
- 10350181
- Editor(s):
- Nicole Riemer
- Date Published:
- Journal Name:
- Aerosol Science and Technology
- ISSN:
- 0278-6826
- Page Range / eLocation ID:
- 1 to 20
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/02786826.2022.2114313
