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Quantum chemical studies on atmospheric sulfuric acid nucleation

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Finnish Meteorological Institute: Veli-Matti Kerminen. ... University of Oulu, Department of Chemistry: Kari Laasonen, Chang-Geng Ding. ... – PowerPoint PPT presentation

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Title: Quantum chemical studies on atmospheric sulfuric acid nucleation


1
Quantum chemical studies on atmospheric sulfuric
acid nucleation
  • Theo Kurtén
  • Division of Atmospheric Sciences
  • Department of Physical Sciences
  • University of Helsinki
  • 08.11.2007

2
Co-authors
  • University of Helsinki, Department of Physical
    Sciences Hanna Vehkamäki, Ismael Kenneth Ortega,
    Ville Loukonen, Martta Salonen, Leena Torpo,
    Markku Kulmala.
  • Finnish Meteorological Institute Veli-Matti
    Kerminen.
  • University of Helsinki, Department of Chemistry
    Markku Sundberg.
  • University of Oulu, Department of Chemistry
    Kari Laasonen, Chang-Geng Ding.
  • University of Tartu Madis Noppel.

3
New-particle formation is observed frequently in
the atmosphere
  • but the molecular-level mechanisms behind these
    nucleation events are unknown.
  • Events seem to be connected with sulfuric acid
    (H2SO4) concentrations, and sometimes also
    ammonia (NH3).

Diameter (m)
Time
4
Suggested nucleation mechanisms
  • Binary H2SO4-H2O
  • Ternary H2SO4-H2O-NH3
  • Ion-induced H2SO4-H2O
  • H2SO4 organics

5
Quantum Chemistry
  • The numerical solution of Schrödingers
    equation for a system of atomic nuclei and
    electrons subject to various approximations.
  • Approximations are made e.g. regarding the shape
    of the wavefunction and the treatment of
    electron-electron correlation
  • Different sets of approximations ? different
    model chemistries
  • denoted by a bewildering multitude of acronyms
  • We have recently used quantum chemistry to
    investigate sulfuric acid water ammonia
    nucleation in the atmosphere.

6
NH3 enhances formation of neutral clusters, but
the effect only becomes apparent when n(H2SO4) ?
2. For ionic clusters, NH3 has little or no
effect.
  • Gibbs free energies of formation for clusters
    with
  • 2-4 sulfuric acid molecules
  • T 265 K
  • H2SO4 0.36 ppt
  • NH3 1 ppb
  • HSO4- 3000 cm-3

Blue clusters with NH3 Red clusters without
NH3 Solid lines neutral clusters Dashed lines
ionic clusters
RI-CC2/aug-cc-pV(Td)Z energies with BLYP/DZP
geometries frequencies. Data by I.K. Ortega.
7
However, NH3H2SO4 mole ratio almost always ? 11
RI-MP2/aug-cc-pV(Td)Z energies with
RI-MP2/aug-cc-pV(Dd)Z geometries frequencies.
s.a. sensitivity analysis frequencies scaled
by 0.75 and -2 kcal/mol added to the energy of
each ammonia addition step.
typical atmospheric range
8
The problem with sulfuric acid ammonia - water
nucleation
  • It might not be (only) sulfuric acid
  • Threshold H2SO4 concentration for nucleation
    (Berndt et al.)
  • 1010 cm-3 if taken from a liquid reservoir
  • 107 cm-3 if produced from SO2 H2O UV
  • ? Some other SO2 oxidation products participate!
  • and it might not be ammonia, either.
  • Measurements and calculations (e.g. Murphy et
    al.) show that amines, rather than ammonia, may
    be the primary enhancers of atmospheric nitric
    acid nucleation
  • Our calculations indicate that this is likely to
    be the case for sulfuric acid nucleation, too.
  • (Water is probably still a safe bet, though.)

9
Comparison of sulfuric acid and peroxo-disulfuric
acid dimers (data by M. Salonen)
RI-MP2/QZVPP
H2SO4?H2SO4, H2SO4?H2S2O8, ?E0-18.0,
?G?-6.2 kcal/mol ?E0-20.2, ?G?-4.7 kcal/mol
H2SO4?H2SO4?H2O, H2SO4?H2S2O8?H2O, ?E0-33.0,
?G?-7.3 kcal/mol ?E0-37.4, ?G?-8.7 kcal/mol
10
Amines much more strongly bound than NH3 to
H2SO4, and somewhat more strongly to HSO4-
H2SO4?NH3, ?G?-6.6 kcal/mol H2SO4?(CH3)2NH,
?G?-13.7 kcal/mol
HSO4-?NH3, ?G?1.8 kcal/mol HSO4-?(CH3)2NH,
?G?-0.7 kcal/mol
Computed using RI-CC2/aug-cc-pV(Td)Z energies
and RI-MP2/aug-cc-pV(Dd)Z geometries
frequencies. Data provided by V. Loukonen.
11
Amines also promote addition of H2SO4 to both
neutral and ionic clusters much more effectively
than NH3
Reaction ?G?, kcal/mol
H2SO4 H2SO4 ? (H2SO4)2 -6.9
H2SO4NH3 H2SO4 ? (H2SO4)2NH3 -14.4
H2SO4(CH3)2NH H2SO4 ? (H2SO4)2(CH3)2NH -19.3
HSO4- H2SO4 ? HSO4-H2SO4 -34.1
HSO4-NH3 H2SO4 ? HSO4-H2SO4NH3 -34.7
HSO4-(CH3)2NH H2SO4 ? HSO4-H2SO4(CH3)2NH -42.0
Computed using RI-CC2/aug-cc-pV(Td)Z energies
and RI-MP2/aug-cc-pV(Dd)Z geometries
frequencies.
12
Conclusions
  • NH3 significantly assists the growth of
    atmospheric clusters in the H2SO4 co-ordinate
  • However, amines are likely to be even more
    effective, and might actually be the main
    enhancers of nucleation.
  • The NH3H2SO4 mole ratio of nucleating clusters
    in atmospheric conditions likely to be between
    13 and 11.
  • NH3 probably plays only a small role in
    ion-induced nucleation.
  • Amines, on the other hand, might be important
  • H2S2O8 might also play a role in atmospheric
    nucleation (along with or even instead of H2SO4).

13
References
  • Articles by us
  • T. Kurtén et al. Atmos. Chem. Phys. 2007, 7,
    2765 (NH3H2SO4 mole ratio) Boreal Env. Res.
    2007, 12, 431 (H2SO4 hydration, ions)
  • V. Loukonen et al. J. Phys. Chem. A 2007,
    submitted (amines)
  • M. Salonen et al. Atmos. Res. 2007, submitted
    (SO2 oxidation intermediates)
  • L. Torpo et al. J. Phys. Chem. A 2007, 111,
    10671 (role of NH3)
  • Articles by others
  • S. M. Ball et al. J. Geophys. Res. 1999, D104,
    237098. (experiments on NH3 nucleation)
  • T. Berndt et al. Science 2005, 307, 698
    Geophys. Res. Lett. 2006, 33, L15817 (H2SO4 and
    SO2 nucleation experiments)
  • D. Hanson F. Eisele J. Phys. Chem. A 2000,
    104, 1715 (H2SO4 hydration)
  • S. M. Murpy et al. Atmos. Chem. Phys. 2007, 7,
    2313 (amines)
  • A. Nadykto F. Yu Chem. Phys. Lett. 2007, 435,
    14 (H2SO4-NH3-H2O clusters)
  • Programs used
  • Gaussian 03 by Frisch et al. (Gaussian Inc. 2004)
  • SIESTA version 2.0 by Soler Artacho et al.
  • Turbomole version 5.8. by Alhrichs et al.

14
Acknowledgements
  • CSC center for computer science
  • Johanna Blomqvist, Nino Runeberg, Mikael
    Johansson
  • Academy of Finland

15
Thank you for your attention!
  • Mange tak for er opmærksomhed!
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