AIMIS LABORATORY
Dr. Paul Cooper, Department of Chemistry and Biochemistry
pcooper6@gmu.edu – 703–993-2403
Chemistry and Contrails
Chemistry and Contrails
• Hydrated Molecular Complexes
- Radiative Balance
- Nucleation of aerosols
• Photochemistry
- Molecular complexes
- Ices
• Laboratory Capabilities and Methods
Chemistry and Contrails
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
Chemistry and Contrails
O
H
H
Chemistry and Contrails
Higher electronegativity of O atom pulls electron
density away from H atoms and produces an electric
dipole.
-
O
+H
+H
Chemistry and Contrails
-
O
+H
+H
Chemistry and Contrails
Dipole-dipole intermolecular bond.
-
O
+H
+H
+
-
Chemistry and Contrails
Dispersion force intermolecular bond.
-
O
+H
Induced
dipole
+H
-
+
Chemistry and Contrails
Hydrogen-bonded intermolecular bond.
-
O
+H
+H
-
O
+H
+H
Chemistry and Contrails
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!
Chemistry and Contrails
Kjaergaard et al, 2003
Chemistry and Contrails
• In the wake of aircraft the molecular collision crosssection should be greater than ambient atmospheric
conditions.
• Will this increase the local population of molecular
complexes?
• Why are molecular complexes important?
Chemistry and Contrails
• Molecular complexes can absorb radiation at
wavelengths different from their parent molecules.
Low et al., 1999
Chemistry and Contrails
• Intensities of absorption bands can alter significantly!
Cooper et al., 2003
Chemistry and Contrails
• 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.
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?
Chemistry and Contrails
H2O-SO2 complex first
identified in 1988.
Tarbuck et al., 2005
Chemistry and Contrails
• 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
Chemistry and Contrails
• 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.
Chemistry and Contrails
• Ozone depletion
• NOx reacts with Cl and ClO that are ozone
destroying.
• NOx adsorbs onto aerosol and forms HNO3
Chemistry and Contrails
• 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.
Chemistry and Contrails
• 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.
Chemistry and Contrails
• Facility to study these complexes and ices is being
built at GMU.
• Base temperature of 4 K.
• Facility should be operational by early 2008.
Chemistry and Contrails
hl
Chemistry and Contrails
• Reflection or
absorption
• 200 – 28,000 nm
• Matrix-isolation
and ices
Chemistry and Contrails
• 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
pcooper6@gmu.edu