1 / 13

Spectrometry and Photochemistry

Spectrometry and Photochemistry . Theodore S. Dibble Chemistry Department SUNY-Environmental Science and Forestry Syracuse, NY. Role of Spectrometry and Photochemistry. Light flux, F( l ), vs. wavelength, altitude, etc. Photochemistry as fate of a molecule Photolysis as radical source

griselda
Download Presentation

Spectrometry and Photochemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Spectrometry and Photochemistry Theodore S. Dibble Chemistry Department SUNY-Environmental Science and Forestry Syracuse, NY

  2. Role of Spectrometry and Photochemistry • Light flux, F(l), vs. wavelength, altitude, etc. • Photochemistry as fate of a molecule • Photolysis as radical source • Greenhouse gas absorbances • Concentration Measurement

  3. Beer-Lambert Law Absorbance A= ln (Io/I) base e not base 10 I Io A = slc s= absorption cross-section (per molecule) cm2/molecule (s= e 3.8  10-21) c = concentration (molecules cm-3) l in cm

  4. A =3.3 Example Between 40 and 50 km, [O3] ~ 3 x 1011 molecules cm-3 s254 nm = 1.1 x 10-17 cm2 molecule-1 Calculate Absorbance over the 10 km (106 cm)

  5. Light Intensity Solar Zenith Angle – angle from perpendicular (season, time of day, latitude: see Spreadsheet) Other Factors Clouds Albedo (reflectivity) Eccentricity

  6. Why SZA Matters- Pathlength Absorbance & scatter lo l = lo /cos(SZA) SZA=0 SZA=40

  7. Ozone UV Spectrum Wavelength in nm

  8. Photolysis Rate Constant, J Solar flux: F(l) Absorption cross section:s(l) Quantum yield for photolysis: f(l) (fraction of photons absorbed that cause decomposition) Ozone Photolysis Rate = JO3[O3]

  9. Numerical Integration Spreadsheet: www.esf.edu/chemistry/dibble/fch511/calculateJ.xls Exercise: Calculate J for O3 or HOOH at ground level Use absorption cross-sections from JPL Data Evaluation #14 Assume f =1

  10. Photolytic Production of Radicals O3 + hn→ O2 (3S)+ O(3P) ground state products O3 + hn → O2 (1D)+ O(1D) excited state products O(1D) much more reactive than O(3P) Rate of production of O(1D) = Rate of production of O(3P) =

  11. Quantum Yield for O (1D) from O3 Explain the altitude dependence of J(O(1D)) vs. J(O(3P))

  12. Key Points • Ozone UV absorption dominatesF(l) • F(l) depends on SZA • Photolysis rate constants readily calculable

More Related