Title: Quantum chemical studies on atmospheric sulfuric acid nucleation
1Quantum chemical studies on atmospheric sulfuric
acid nucleation
- Theo Kurtén
- Division of Atmospheric Sciences
- Department of Physical Sciences
- University of Helsinki
- 08.11.2007
2Co-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.
3New-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
4Suggested nucleation mechanisms
- Binary H2SO4-H2O
- Ternary H2SO4-H2O-NH3
- Ion-induced H2SO4-H2O
- H2SO4 organics
5Quantum 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.
6NH3 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.
7However, 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
8The 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.)
9Comparison 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
10Amines 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.
11Amines 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.
12Conclusions
- 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).
13References
- 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.
14Acknowledgements
- CSC center for computer science
- Johanna Blomqvist, Nino Runeberg, Mikael
Johansson - Academy of Finland
15Thank you for your attention!
- Mange tak for er opmærksomhed!