Department of Chemistry CHEM1020 General Chemistry ***********************************************

1. Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel: 931-6325 Email: hzhang@tntech.edu

2. CHEM1020/General Chemistry_________________________________________Chapter 12. (L21)-Chemistry of Earth • Today’s Outline …The atmosphere structure chemical composition …The good ozone basic stratosphere ozone chemistry “ozone hole”

3. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Macroscopic physical perspective Etymology for atmosphere: Atmo-: meaning air; Gk, from atmos, meaning vapor, smoke …Structure of the atmosphere Homosphere (~90 km thick), roughly homogeneous atmospheric composition in terms of proportions of its component gases: .troposphere (~0-10~17 km) .stratosphere (~10~17-30 km) .mesosphere (~30-80 km) .thermosphere (~80-90, > ~80 km)

4. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Macroscopic physical perspective …Structure of the atmosphere Heterosphere (> ~90 km to a indefinite upper limit), varying in composition: .N2 (MW = ~28) layer (~90-200 km) .O (AW = ~16) layer (~200-1100 km) .He (AW = ~4) layer (~110-3500 km) .H (AW = ~1) layer (~3500-10000 km, a diffuse layer, 10000 km is an arbitrary boundary upper limit, where the interplanetary space is encountered) -The order of the location of each layer in the heterosphere is manifestation of the gravitational force of the earth

5. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Macroscopic physical perspective …Thickness of each earthsphere: A comparison -thickness of the earth: ~6400 km in radius -thickness of the atmosphere: ~90 km (earth radius:atmosphere = ~71:1) -thickness of the stratosphere: ~20 km (earth radius:stratosphere = ~320:1 -thickness of the troposphere: ~10-17 km (earth radius:troposphere = ~640-376:1) -thickness of ocean: ~4 km (earth radius:ocean = 1600:1) -thickness of the biosphere: < ~0.1 km -thickness of the pedosphere: < ~0.005 km

6. Chapter 12. (L21)-Chemistry of Earth • The atmosphere …Macroscopic physical perspective Physical characterization of the atmosphere: -temperature (most important, like for lakes) -pressure (next important) -density -solar radiation -humidity Stratification of the atmosphere in terms of temperature (pressure, density): temperature profile of the atmosphere

7. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Microscopic perspective …The atmospheric world not a polymer world small molecules volatile molecules trace chemical substances highly oxidizing environment sun-lit

8. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Microscopic perspective …Elemental composition of the atmosphere N, O, C, S, H, Ar, He, Cl, F, Br, other trace elements in aerosols and droplets (Fe, Mn, etc.) …Molecular composition of the atmosphere H/O containing compounds (HxOx, from H2, O2, to H2O, including those oxygen free radicals) C-containing compounds N-containing compounds S-containing compounds X (halogen)-compounds -N2, O2, CO2, H2O, and other molecules, these are the major molecules present in relatively large portion in the atmosphere

9. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: Microscopic perspective …Sources of atmospheric compounds A. Natural emissions -volcano eruption caused injection, even to as high as stratosphere -photosynthesis -biosphere emissions -biomass burning (a very important, hot subject for research) -ocean emissions -terrestrial geological surface emissions -addition from outer space B. Anthropogenic emissions -power-plants (fossil fuel) -automobiles -other industrial emissions

10. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …Basic physical characteristics of the stratosphere -Solar radiation profile: 175-290 nm available with some 100-175 nm, (>290 nm for troposphere) -Temperature profile: below 0 °C, but increasing with height …Role of ozone (O3) in the stratosphere (1) UV absorption/protection/life (2) causing T increasing in stratosphere

11. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …Basic ozone chemistry in the stratosphere The Chapman theory of ozone chemistry: O2 + hν → O + O (180-240 nm) slow (1)   O + O2 + M → O3 + M rapid (2)   O3 + hν → O2 + O (200-300 nm) (3) O3 + O → O2 + O2 (4) where M = N2 and O2 Primary source of O3: Reaction 1; primary sink of O3: Reaction 4. …The Chapman model is a static, pure-O2, photochemical steady-state model

12. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …Source and sink of ozone: Primary source of O3: Reaction 1; primary sink of O3: Reaction 4. …This is a simplified mechanism, proposed in 1930. Later on, new experiments and measurements indicated that the actual mechanism was more complicated, with more pathways and other trace atmospheric chemicals involved.

13. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …The “ozone hole” or ozone depletion Historical event: Ozone hole refers to the large drop of stratospheric O3 levels over Antarctic in the Southern Hemisphere spring of each year The first report came from British scientists in 1985 that the measurements of O3 in the Antarctic showed a ~30% decrease in total O2 aboundance each October (i.e., in the polar spring) since 1977. The findings later were confirmed by satellite measurements. From 1988 to 1997, the depletion, up to ~70%, mostly 12-20 km, occupied an area larger than the Antarctic continent.

14. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …Basic chemistry of ozone disappearance in the polar region, what CFC can do to destroy the ozone in the stratosphere? CFCs undergoes photolysis at 185-210 nm:   CFCl3 + hν → CFCl2 + Cl CFCl2 + hν → CFCl + Cl Reactions destroying O3 by chlorine:   Cl + O3 → ClO + O2 ClO + O → Cl + O2 Net: O3 + O → O2 + O2

15. Chapter 12. (L21)-Chemistry of Earth • The atmosphere: The good ozone …Consequences of O3 depletion: -more UV -skin cancer -disturbance of the biosphere, DNA, immune system, -others, etc.

16. Chapter 12. (L21)-Chemistry of Earth Quiz Time TBA.