Methylamine is found in both the gas and aqueous phases in the atmosphere. It has been shown to form light-absorbing, oligomeric species in reactions with methylglyoxal and other aldehyde species in bulk aqueous-phase experiments and when mixed into seed aerosol as a sulfate salt. However, when droplets containing methylamine, methylglyoxal, and ammonium sulfate (AS) were dried and collected on a filter, browning was the same as in bulk solution, indicating that excess methylamine quickly evaporated from aerosol. We therefore explored gas-phase methylamine’s influence on aerosol production, properties, and molecular composition. When methylglyoxal aerosol particles were exposed to 2 ppm methylamine gas in a chamber, rapid browning was observed, but not growth. Aerosol bounce measurements indicated that particles became slightly more viscous and hydrophobic upon methylamine exposure. Subsequent cloud processing increased both viscosity and hygroscopicity, consistent with high-resolution mass spectrometry results showing that aerosol oligomer dicarbonyl functional groups were derivatized to cationic imidazole rings. Photolytic cloud processing triggered the incorporation of hydryoxyacetone and acetal radicals into oligomers, further increasing aerosol viscosity. Since dicarbonyl species are a major component of atmospheric aerosol particles, these results suggest that methylamine exposure and cloud processing will slowly increase brown carbon content, viscosity, and hygroscopicity of atmospheric aerosol.

Effects of gas-phase methylamine and cloud processing on aerosol chemistry, water uptake, viscosity, and optical properties

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.