Effects of mixing state on water-uptake properties of ammonium sulfate – Organic mixtures

Abstract

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 hygroscopicities, 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.

Copyright © 2022 American Association for Aerosol Research

Graphical Abstract

SYNOPSIS STATEMENT

This work provides water-uptake measurements of mixed aerosol particles that are prevalent in the atmosphere that can be useful in improving climate models.

Data availability

The data is available upon request from the corresponding authors as stated.

Author contributions

PNR and KAM, TMR, DDD, AAA designed and conducted the CCN and H-TDMA experiments. KD, JND, and MAF conducted experiments, and performed the calculations using the CRDS data. PNR conducted modeling analysis across all three data sets and prepared the manuscript with input from all the coauthors.

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

PNR, KAM, and AAA acknowledge support from the NSF: AGS-1723920 and AGS-2124489. KD, JND, MAF acknowledge support from NSF: AGS-2124490. PNR and JND also acknowledge support from NSF GRFP Awards (1840340 & 1255832). DDD and TMR acknowledge support from the NSF: AGS-2124491.