1. Chemistry and Contrails
AIMIS LABORATORY
Dr. Paul Cooper, Department of Chemistry and Biochemistry
– 703–
Chemistry and Contrails

2. Chemistry and Contrails
Hydrated Molecular Complexes
- Radiative Balance
- Nucleation of aerosols
Photochemistry
- Molecular complexes
- Ices
Laboratory Capabilities and Methods

3. Chemistry and Contrails

4. Chemistry and Contrails
What are molecular complexes?
Molecular complexes are formed when two (or more) molecules stick together because of intermolecular bonding.
Chemical reaction - A + B  C + D
Complex formation - A + B  AB
Complexes are often transient

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Higher electronegativity of O atom pulls electron density away from H atoms and produces an electric dipole. - H O + +

7. Chemistry and Contrails- H O + +
O=C=O

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Dipole-dipole intermolecular bond. - H O + + - +
O=C=O -

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Dispersion force intermolecular bond. - H O - +
Induced dipole + +
O=O

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Hydrogen-bonded intermolecular bond. - H O + + H O

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Relative strengths of intermolecular bonding
Hydrogen bonding – 10
Dipole-dipole – 2
Dispersion forces – <0.5
Type and strength of bond will determine the lifetime of a complex in the atmosphere. However, lifetime is not a good indicator of abundance!

12. Chemistry and Contrails
Kjaergaard et al, 2003

13. Chemistry and Contrails
In the wake of aircraft the molecular collision cross-section should be greater than ambient atmospheric conditions.
Will this increase the local population of molecular complexes?
Why are molecular complexes important?

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Molecular complexes can absorb radiation at wavelengths different from their parent molecules.
Low et al., 1999

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Intensities of absorption bands can alter significantly!
Cooper et al., 2003

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Hydrated complexes are being studied using both theoretical and experimental methods to determine absorption band wavelength and intensity shifts.
Field has boomed over the last 10 years.
Hydrated-complexes in the atmosphere are just being recognized as contributors to radiative forcing.
The contribution of hydrated-complexes formed in the wake of aircraft to the radiative balance of the Earth has not been assessed.

17. Chemistry and Contrails
Complex formation is the first step in the nucleation of aerosols – fundamental to our understanding of nucleation.
Theoretical studies of nucleation involve sequentially adding water molecules.
Dynamics of nucleation
How does the reactivity of a molecule change upon formation of a hydrated complex?

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H2O-SO2 complex first identified in 1988.
Tarbuck et al., 2005

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Photochemistry of hydrated-complexes
H2SO4 is transparent in UV >140 nm.
Near-IR pumping of OH overtone can dissociate H2SO4
Dissociation is predicted to be more efficient in the H2SO4-H2O complex than H2SO4 monomer.
Vaida et al., 2003

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Stratospheric aerosol layer.
H2SO4/H2O aerosol
Natural source of sulfur to the stratosphere is biogenic and geological sources of OCS.
What is the impact of sulfur emissions from aviation on the stratospheric aerosol layer?
Radiative balance – reflects solar radiation to cool Earth – but can also absorb IR radiation to trap heat.

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Ozone depletion
NOx reacts with Cl and ClO that are ozone destroying.
NOx adsorbs onto aerosol and forms HNO3

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Photochemistry of ices
Water ice with adsorbed CO2 can enhance H2O2 production when photolyzed. Solid carbonic acid ice may also be formed.
Water ice adsorbed with SO2 may provide an additional source of H2SO4 when photolyzed.

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Molecular complexes can be produced in and studied using the matrix-isolation technique.
Matrix-isolation involves trapping reactive or unstable molecules in solid inert gas hosts such as Ne and Ar.
The inert gas provides a pseudo gas-phase environment due to negligible intermolecular interactions.
Inert gases are also transparent in the UV, vis and IR regions of the spectrum.

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Facility to study these complexes and ices is being built at GMU.
Base temperature of 4 K.
Facility should be operational by early 2008.

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Reflection or absorption
200 – 28,000 nm
Matrix-isolation and ices

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Hydrated molecular complexes are important throughout the atmosphere.
They are also very relevant in understanding the chemistry of contrails at their most fundamental level.
There is a lot of chemistry still to learn, but the tools are there to do it.
Dr. Paul Cooper