Dimethylamine as a Major Alkyl Amine Species in Particles and Cloud Water: Observations in Semi-Arid and Coastal Regions

Abstract:

Aerosol and cloud water measurements of dimethylamine (DMA), the most abundant amine in this study, were conducted in semi-arid (Tucson, Arizona) and marine (Nucleation in California Experiment, NiCE; central coast of California) areas. In both regions, DMA exhibits a unimodal mass size distribution with a dominant peak between 0.18 – 0.56 μm. Aminium salt formation is likely the dominant path for DMA into particles, but DMA can partition to coarse particle (e.g., dust, sea salt) surfaces too. The ratio of DMA to ammonium for bulk aerosol reaches up to 8% and 15% for Tucson and NiCE, respectively. Marine biogenic emissions are shown to be a significant source of DMA, with DMA being over three times as high during NiCE versus at Tucson. Wildfires during NiCE did not impact the mass size distribution of particulate DMA; conversely, significant DMA concentration enhancements were observed in cloud water due to dissolution. It is likely that DMA, similar to nitrate, volatilizes after drop evaporation, which is why enhancements were not observed in surface or airborne aerosol measurements. PM_1.0 data in Tucson show the following: (i) year-long DMA concentrations are positively correlated with factors that enhance sulfate formation, biogenic volatile organic compound emissions, and aerosol-phase water; and (ii) DMA concentrations exhibit positive correlations with various trace elements, most especially vanadium, which warrants additional investigation.