quantum chemical studies on atmospheric sulfuric acid nucleation

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

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Quantum chemical studies on atmospheric sulfuric acid nucleation. Theo Kurt é n Division of Atmospheric Sciences Department of Physical Sciences University of Helsinki 08.11.2007. Co-authors. - PowerPoint PPT Presentation

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Page 1: Quantum chemical studies on atmospheric sulfuric acid nucleation

Quantum chemical studies on

atmospheric sulfuric acid nucleation

Theo Kurtén

Division of Atmospheric Sciences

Department of Physical Sciences

University of Helsinki

08.11.2007

Page 2: Quantum chemical studies on atmospheric sulfuric acid nucleation

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.

Page 3: Quantum chemical studies on atmospheric sulfuric acid nucleation

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).

Time

Dia

mete

r (m

)

Page 4: Quantum chemical studies on atmospheric sulfuric acid nucleation

Suggested nucleation mechanisms:

Binary H2SO4-H2O

Ternary H2SO4-H2O-NH3

Ion-induced H2SO4-H2O

H2SO4 + organics

Page 5: Quantum chemical studies on atmospheric sulfuric acid nucleation

Quantum Chemistry

= The numerical solution of Schrödinger’s 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.

Page 6: Quantum chemical studies on atmospheric sulfuric acid nucleation

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

-10

0

10

20

30

40

2 3 4

number of acids

RI-CC2/aug-cc-pV(T+d)Z energies with BLYP/DZP geometries & frequencies.Data by I.K. Ortega.

Page 7: Quantum chemical studies on atmospheric sulfuric acid nucleation

However, NH3:H2SO4 mole ratio almost always 1:1

|typical atmospheric range|

RI-MP2/aug-cc-pV(T+d)Zenergies with RI-MP2/aug-cc-pV(D+d)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.

Page 8: Quantum chemical studies on atmospheric sulfuric acid nucleation

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.)

Page 9: Quantum chemical studies on atmospheric sulfuric acid nucleation

Comparison of sulfuric acid and peroxo-disulfuric acid dimers (data by M. Salonen)

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

RI-MP2/QZVPP

Page 10: Quantum chemical studies on atmospheric sulfuric acid nucleation

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(T+d)Z energies and RI-MP2/aug-cc-pV(D+d)Z geometries & frequencies. Data provided by V. Loukonen.

Page 11: Quantum chemical studies on atmospheric sulfuric acid nucleation

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

H2SO4·NH3 + H2SO4 (H2SO4)2·NH3 -14.4

H2SO4·(CH3)2NH + H2SO4 (H2SO4)2·(CH3)2NH -19.3

HSO4- + H2SO4 HSO4

-·H2SO4 -34.1

HSO4-·NH3 + H2SO4 HSO4

-·H2SO4·NH3 -34.7

HSO4-·(CH3)2NH + H2SO4 HSO4

-

·H2SO4·(CH3)2NH

-42.0

Computed using RI-CC2/aug-cc-pV(T+d)Z energies and RI-MP2/aug-cc-pV(D+d)Z geometries & frequencies.

Page 12: Quantum chemical studies on atmospheric sulfuric acid nucleation

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 NH3:H2SO4 mole ratio of nucleating clusters in

atmospheric conditions likely to be between 1:3 and 1:1. 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).

Page 13: Quantum chemical studies on atmospheric sulfuric acid nucleation

References

Articles by us T. Kurtén et al.: Atmos. Chem. Phys. 2007, 7, 2765 (NH3:H2SO4 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.

Page 14: Quantum chemical studies on atmospheric sulfuric acid nucleation

Acknowledgements

CSC center for computer scienceJohanna Blomqvist, Nino Runeberg, Mikael

Johansson

Academy of Finland

Page 15: Quantum chemical studies on atmospheric sulfuric acid nucleation

Thank you for your attention!

Mange tak for er opmærksomhed!