Chemistry and Contrails 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

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

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

Chemistry and Contrails Dipole-dipole intermolecular bond. - H O + + - + O=C=O -

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

Chemistry and Contrails - + Hydrogen-bonded intermolecular bond. - H O + + H O

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 cross-section 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