Glyoxal as a Potential Source of Highly Viscous Aerosol Particles

Recent studies have shown that glyoxal may remain in the particle phase of aqueous aerosol particles upon drying despite the high vapor pressure of pure glyoxal, due to the formation of oligomeric glyoxal water adducts with low vapor pressure. Little is known about the phase state of such particles, even though some studies suggested a semisolid or glassy state for dried aqueous glyoxal solutions. In this study, we performed glass transition temperature (T-g) measurements on various aqueous glyoxal systems. We show experimentally that very slow and also fast drying of aqueous glyoxal solutions can indeed lead to the formation of highly viscous semisolid and glassy states, both in bulk as well as in aerosolized samples. T-g changes with the solute concentration before drying, with drying rate and in the presence of additional solutes such as ammonium sulfate or ammonium bisulfate, even when they are present only in catalytic amounts. Temperature-dependent measurements show that the equilibration between various glyoxal species upon water addition, mimicking atmospheric water uptake upon rising humidity, can range from hours to days. We use the measured glass transition temperatures to infer dependencies of the aqueous phase equilibria between monomer, dimer, and trimer glyoxal species and their water adducts and support these by infrared spectroscopy. Our results imply that aqueous glyoxal aerosols may form highly viscous states at atmospherically relevant conditions..

Automated summary

This study experimentally demonstrates that aqueous glyoxal solutions can form highly viscous semisolid and glassy states upon drying, both in bulk and aerosolized samples. The glass transition temperatures measured in this study provide insights into the phase equilibria of glyoxal species in the aqueous phase, suggesting the formation of highly viscous states in atmospheric conditions.