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IV. Ozone Hole Observations Heterogeneous chemistry Decadal ozone loss

IV. Ozone Hole Observations Heterogeneous chemistry Decadal ozone loss. Vertical [O 3 ] Profile at One Site. Column Densities of O 3. 1 D.U. = 2.7 x 10 16 molecules cm -2. Color-Coded Map of Column O 3. Chlorine Chemistry Critical …. …But Meteorology Also Critical.

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IV. Ozone Hole Observations Heterogeneous chemistry Decadal ozone loss

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  1. IV. Ozone Hole ObservationsHeterogeneous chemistryDecadal ozone loss

  2. Vertical [O3] Profile at One Site

  3. Column Densities of O3 1 D.U. = 2.7 x 1016 molecules cm-2

  4. Color-Coded Map of Column O3

  5. Chlorine Chemistry Critical …

  6. …But Meteorology Also Critical Polar Vortex isolates air mass (no NOx gets in from outside) Very cold (195 K, clouds form)

  7. Sequence of Events Late Fall/Early Winter - not much light - radicals all in reservoirs Mid Winter - gets cold, clouds form - reactions on clouds sequester NOx not ClOx reservoirs: ClONO2(g) + HCl (surf) → HOCl (g, surf) + HONO2 (surf) HOCl + HCl (surf) → Cl2 (g) + HOH (surf)

  8. Sequence of Events Early Spring – gas phase chemistry HOCl + hn → OH + Cl Cl2 + hn → 2 Cl 2 {Cl + O3 → ClO +O2} ClO + ClO → ClOOCl ClOOCl + hn → 2 Cl + O2 (net) 2 O3 → 3O2

  9. Sequence of Events Late Spring – heatbreaks up vortex HONO2 evaporates NOx from outside move in ClO + NO2 → ClONO2

  10. Key Points • Rapid, localized, structured • Meteorology and Chemistry • Timeline (Winter) • - Cold enough for new/big particles • NOx reservoirs bind to particles • ClOx reservoirs stay as gas • Timeline (Spring) • - light starts run-away chemistry • - eventual warming normalizes chemistry

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