On the composition of ammonia-sulfuric-acid ion clusters during aerosol particle formation

Autor(en)

S. Schobesberger, A. Franchin, F. Bianchi, L. Rondo, J. Duplissy, A. Kuerten, I. K. Ortega, A. Metzger, R. Schnitzhofer, J. Almeida, A. Amorim, J. Dommen, E. M. Dunne, M. Ehn, S. Gagne, L. Ickes, H. Junninen, A. Hansel, V-M Kerminen, J. Kirkby, A. Kupc, A. Laaksonen, K. Lehtipalo, S. Mathot, A. Onnela, T. Petäjä, F. Riccobono, F. D. Santos, M. Sipilä, A. Tome, G. Tsagkogeorgas, Y. Viisanen, Paul Wagner, D. Wimmer, J. Curtius, N. M. Donahue, U. Baltensperger, M. Kulmala, D. R. Worsnop

Abstrakt

The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH

₃) and sulfuric acid (H

₂SO

₄). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH

₃-H

₂SO

₄ clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH

₃] in the range from < 2 to 1400 pptv, [H

₂SO

₄] from 3.3 × 106 to 1.4 × 109 cm

^-1 (0.1 to 56 pptv), and a temperature range from -25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH

₃ and H

₂SO

₄, and then grew to larger clusters containing more than 50 molecules of NH

₃ and H

₂SO

₄, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH

₃-H

₂SO

₄ clusters is primarily determined by the ratio of gas-phase concentrations [NH

₃]/[H

₂SO

₄], as well as by temperature. Pure binary H

₂O-H

₂SO

₄ clusters (observed as clusters of only H

₂SO

₄) only form at [NH

₃]/[H

₂SO

₄] < 0.1 to 1. For larger values of [NH

₃]/[H

₂SO

₄], the composition of NH

₃-H

₂SO

₄ clusters was characterized by the number of NH

₃ molecules m added for each added H

₂SO

₄ molecule n (Δm/Δ n), where n is in the range 4-18 (negatively charged clusters) or 1-17 (positively charged clusters). For negatively charged clusters, Δ m/Δn saturated between 1 and 1.4 for [NH

₃]/[H

₂SO

₄] > 10. Positively charged clusters grew on average by Δm/Δn Combining double low line 1.05 and were only observed at sufficiently high [NH

₃]/[H

₂SO

₄]. The H

₂SO

₄ molecules of these clusters are partially neutralized by NH

₃, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that electrically neutral NH

₃-H

₂SO

₄ clusters, unobservable in this study, have generally the same composition as ionic clusters for [NH

₃]/[H

₂SO

₄] > 10. We expect that NH

₃-H

₂SO

₄ clusters form and grow also mostly by Δm/Δn > 1 in the atmosphere's boundary layer, as [NH

₃]/[H

₂SO

₄] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH

₃-H

₂SO

₄ anion clusters during new-particle formation in the Finnish boreal forest. However, the exact role of NH

₃-H

₂SO

₄ clusters in boundary layer particle formation remains to be resolved.

Organisation(en)

Aerosolphysik und Umweltphysik

Externe Organisation(en)

University of Helsinki, Paul Scherrer Institute, Johann Wolfgang Goethe-Universität Frankfurt am Main, European Organization for Nuclear Research (CERN), Université Lille I - Sciences et Technologies, IONICON Analytik GmbH, Leopold-Franzens-Universität Innsbruck, Universidade de Lisboa, Universidade da Beira Interior, University of Leeds, Finnish Meteorological Institute, University of Eastern Finland, Leibniz-Institut für Troposphärenforschung, Carnegie Mellon University, Aerodyne Res Inc

Journal

Atmospheric Chemistry and Physics

Band

15

Seiten

55-78

Anzahl der Seiten

24

ISSN

1680-7316

DOI

https://doi.org/10.5194/acp-15-55-2015

Publikationsdatum

01-2015

Peer-reviewed

Ja

ÖFOS 2012

103037 Umweltphysik, 103039 Aerosolphysik

Schlagwörter

ASJC Scopus Sachgebiete

Atmospheric Science

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/2995ef4f-6651-40ea-bd66-05a01c383d24