Department of Chemistry CHEM1020 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

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”

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)

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:.N 2 (MW = ~28) layer (~ km).O (AW = ~16) layer (~ km).He (AW = ~4) layer (~ km).H (AW = ~1) layer (~ km, a diffuse layer, 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

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 = ~ :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

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

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

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 (H x O x, from H 2, O 2, to H 2 O, including those oxygen free radicals) C-containing compounds N-containing compounds S-containing compounds X (halogen)-compounds -N 2, O 2, CO 2, H 2 O, and other molecules, these are the major molecules present in relatively large portion in the atmosphere

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

Chapter 12. (L21)-Chemistry of Earth The atmosphere: The good ozone …Basic physical characteristics of the stratosphere -Solar radiation profile: nm available with some nm, (>290 nm for troposphere) -Temperature profile: below 0 °C, but increasing with height …Role of ozone (O 3 ) in the stratosphere (1) UV absorption/protection/life (2) causing T increasing in stratosphere

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

Chapter 12. (L21)-Chemistry of Earth The atmosphere: The good ozone …Source and sink of ozone: Primary source of O 3 : Reaction 1; primary sink of O 3 : Reaction 4. …This is a simplified mechanism, proposed in Later on, new experiments and measurements indicated that the actual mechanism was more complicated, with more pathways and other trace atmospheric chemicals involved.

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 O 3 levels over Antarctic in the Southern Hemisphere spring of each year The first report came from British scientists in 1985 that the measurements of O 3 in the Antarctic showed a ~30% decrease in total O 2 aboundance each October (i.e., in the polar spring) since The findings later were confirmed by satellite measurements. From 1988 to 1997, the depletion, up to ~70%, mostly km, occupied an area larger than the Antarctic continent.

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 nm: CFCl 3 + hν → CFCl 2 + Cl CFCl 2 + hν → CFCl + Cl Reactions destroying O 3 by chlorine: Cl + O 3 → ClO + O 2 ClO + O → Cl + O 2 Net:O 3 + O → O 2 + O 2

Chapter 12. (L21)-Chemistry of Earth The atmosphere: The good ozone …Consequences of O 3 depletion: -more UV -skin cancer -disturbance of the biosphere, DNA, immune system, -others, etc.

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