AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Acid-base Reactive Uptake of Dimethylamine and Nitric Acid onto Nanoparticles: Cluster Simulations and Nanoparticle Composition Measurements
SABRINA CHEE, Nanna Myllys, Kelley Barsanti, Bryan Wong, James Smith, University of California, Irvine
Abstract Number: 158 Working Group: Aerosol Chemistry
Abstract Nanoparticle composition measurements and cluster simulations of particle formation and growth via reactive uptake of nitric acid (HNO3) and dimethylamine (DMA) have been investigated. A flow tube reactor with adjustable reaction time was used to study particle formation from these species under both dry and humid conditions. A Thermal Desorption Chemical Ionization Mass Spectrometer was used to measure size-resolved nanoparticle composition from 9 – 30 nm in diameter, and those results were compared with simulations of clusters up to 1 nm in size to probe the mechanism of reactive uptake. Particles were produced readily in both dry and humid (55% relative humidity, RH) conditions. Humid conditions did not significantly increase particle number concentration but increased the geometric mean diameter of the particle number-size distribution. HNO3-DMA particle composition measurements show that the acid:base ratio remains neutral (1:1) in both RH conditions at all studied sizes. Additionally, cluster simulations strongly suggest that a 1:1 acid-base ratio is the most stable cluster growth pathway due to over 7 orders of magnitude lower evaporation rates compared to other cluster combinations. These results contrast with composition measurements of particles made from sulfuric acid (H2SO4) and DMA as well as NH3, and it is likely that these compositional differences between H2SO4-DMA particles and the particles in this study are due to the components’ volatility. Whereas HNO3 and DMA must neutralize each other to remain in the particle phase, H2SO4 has a low enough volatility that it can contribute to nanoparticle growth without reactive uptake and thus particles are likely to be more acidic. Implications of these observations on ambient nanoparticle composition are discussed.