Applying Single Particle Levitation to Explore the Properties of Aqueous Brown Carbon Aerosol

PRAKRITI SINGH, Erin Bowey, James F. Davies, Paula K. Hudson, University of California, Riverside

     Abstract Number: 244
     Working Group: Aerosol Chemistry

Abstract
Atmospheric aerosols influence air quality, climate, and cloud formation, with brown carbon (BrC) playing a key role due to its ability to absorb solar radiation at visible wavelengths (<450 nm). While BrC is commonly emitted from biomass burning, it can also form through aqueous-phase reactions of water-soluble organic and nitrogen-containing compounds in cloud droplets.

In this work, we investigate the formation of aqueous BrC by reacting methylglyoxal (MeGX) with glycine in bulk solution; mixtures with 1:1, 1:2, and 2:1 molar ratio were aged over 21 days, showing increasing browning and formation of light-absorbing chromophores. Individual droplets from both fresh and aged solutions were levitated in a linear quadrupole electrodynamic balance (LQ-EDB) to measure hygroscopic growth and phase behavior as a function of relative humidity. Preliminary results show that the 1:2 and 2:1 mixtures exhibit increasing hygroscopic growth with aging, while the 1:1 mixture shows no clear trend. The 1:1 droplet appear to form a viscous phase at low RH and do not effloresce, which may limit water loss at lower RH. Additionally, evaporation measurements revealed that pure MeGX droplets evaporate rapidly, but when mixed with glycine, this volatility is suppressed. Ongoing work aims to determine the threshold composition at which MeGX will show its evaporative behavior within the mixture. Overall, these results show that the properties of BrC can change depending on precursor ratios and aging which could affect how these particles behave in the atmosphere.