edu.ucar.opensky::articles:19271 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-26T02:39:53.568747 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d74m9682 Unexpectedly acidic nanoparticles formed in dimethylamine–ammonia–sulfuric-acid nucleation experiments at CLOUD 2016-11-03T00:00:00Z publication https://n2t.org/ark:/85065/d74m9682 https://doi.org/10.5194/acp-16-13601-2016 Lawler, Michael J. author Winkler, P. M. author Kim, J. author Ahlm, L. author Tröstl, J. author Praplan, A. P. author Schobesberger, S. author Kürten, A. author Kirkby, J. author Bianchi, F. author Duplissy, J. author Hansel, A. author Jokinen, T. author Keskinen, H. author Lehtipalo, K. author Leiminger, M. author Petäjä, T. author Rissanen, M. author Rondo, L. author SImon, M. author Sipilä, M. author Williamson, C. author Wimmer, D. author Riipinen, I. author Virtanen, A. author Smith, J. N. author UCAR/NCAR - Library publisher New particle formation driven by acid-base chemistry was initiated in the CLOUD chamber at CERN by introducing atmospherically relevant levels of gas-phase sulfuric acid and dimethylamine (DMA). Ammonia was also present in the chamber as a gas-phase contaminant from earlier experiments. The composition of particles with volume median diameters (VMDs) as small as 10 nm was measured by the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Particulate ammonium-to-dimethylaminium ratios were higher than the gas-phase ammonia-to-DMA ratios, suggesting preferential uptake of ammonia over DMA for the collected 10-30 nm VMD particles. This behavior is not consistent with present nanoparticle physicochemical models, which predict a higher dimethylaminium fraction when NH3 and DMA are present at similar gas-phase concentrations. Despite the presence in the gas phase of at least 100 times higher base concentrations than sulfuric acid, the recently formed particles always had measured base : acid ratios lower than 1 : 1. The lowest base fractions were found in particles below 15 nm VMD, with a strong size-dependent composition gradient. The reasons for the very acidic composition remain uncertain, but a plausible explanation is that the particles did not reach thermodynamic equilibrium with respect to the bases due to rapid heterogeneous conversion of SO2 to sulfate. These results indicate that sulfuric acid does not require stabilization by ammonium or dimethylaminium as acid-base pairs in particles as small as 10 nm. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright Author(s) 2016. This work is distributed under the Creative Commons Attribution 3.0 License. None eng geoscientificInformation