AIMIS LABORATORY Dr. Paul Cooper, Department of Chemistry and Biochemistry firstname.lastname@example.org – 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 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
O H H 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=C=O
O H H Chemistry and Contrails Dipole-dipole intermolecular bond. - + + - + O=C=O -
O H H Chemistry and Contrails Dispersion force intermolecular bond. - Induced dipole + + - O=O +
O O H H H H Chemistry and Contrails Hydrogen-bonded intermolecular bond. - + + - + +
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 • 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 • email@example.com