The unit for absorbed radiation is the “Sievert” ( Sv )

1. The unit for absorbed radiation is the “Sievert” (Sv) • One sievert all at once will make you sick, 5-8 sieverts will kill you. • A microsievert (μSv) is 1 millionth of a sievert. • A millisievert (mSv) is 1 thousandth of a sievert.

4. Composition of the Atmosphere Radiatively and chemically inactive gases Nitrogen (N2) – 78% of lower atmosphere by volume does not react with other substances a neutral substance Just a filler adding inert bulk to the atmosphere Argon (Ar) – just under 1% of surface atmosphere Also largely inert

5. Composition of the Atmosphere Radiatively and chemically active gases Oxygen (O2) - very reactive 21.5% of atmosphere Combines with other substances easily in oxidation Water vapor (H2O↑) – very reactive Can vary greatly in atmospheric concentration (< 1% to >2%) Important greenhouse gas Important to energy transfer and precipitation

6. Anything Special About 21% Oxygen?

7. By 2.5 Billion years ago plankton were altering the oxygen content of the atmosphere

8. Water, Oxygen, Life

9. Where is Earth’s CO2? Rocks - like limestone (and some in plant life and in the ocean)

10. Radiatively and chemically active gases (more) Carbon dioxide (CO2) – important trace gas ~400 ppm Consumed by plants for photosynthesis Important, rapidly increasing greenhouse gas Methane (CH4) – important trace gas Very low concentration ~1800 ppb, but very efficient greenhouse gas Also rapidly increasing concentration Composition of the Atmosphere

11. The Greenhouse Effect What are Greenhouse Gasses? Any gas molecule with two atoms of different elements. Water vapor (H2O) 1-3% Carbon dioxide (CO2) 0.04% Methane (CH4) 0.00018%

12. Aerosols – tiny airborne liquid or solid particles Scatter or absorb solar radiation, cooling surface Sources: Composition of the Atmosphere Dust Meteors Salt Smoke Fuel Burning

13. Atmospheric Pressure & Density • Atmosphere exerts constant pressure on Earth • Atmospheric pressure is weight of air column over a unit of area on surface English: 15lb/in2 Metric: 1 kg/cm2 Air Pressure

14. Air Pressure Change with Altitude • Air pressure decreases with altitude • Near surface, air pressure drops rapidly • Higher in atmosphere, slower drop in pressure • Air at higher altitude less dense, less oxygen • At altitudes > 3000 m, can cause mountain sickness • Symptoms include: • Shortness of breath • Nausea • Headache • Nosebleed

15. Barometer Aneroid • Instrument for measuring atmospheric pressure • Standard unit of atmospheric pressure → millibar • Average surface pressure = 1013.2 millibars (mb) • 2 types of barometer: Mercury

16. Temperature Structure of Atmosphere • In lower atmosphere, temp drops with altitude • Rate of decrease called Lapse Rate (ºC/1000m) • Avgmidlatitude lapse rate = 6.4ºC/1000m • Value called Environmental Lapse Rate (ELR) • ELR varies with atmospheric conditions • Cooling continues to 12-15 km altitude

17. Temperature Structure of Atmosphere

18. Troposphere • Lowest atmospheric layer – 8-16 km thick • All human activity and most weather here • Thicker at Equator, thinner near poles • Temp cools with altitude • Top of troposphere is where temp stops cooling • This level called the tropopause • It separates troposphere from stratosphere above

19. Stratosphere • Lies above the tropopause (~12-50 km altitude) • Contains ozone layer intercepting UV radiation • This causes stratosphere to warm with altitude • Little mixing with air in troposphere • Exception is volcanic eruption • Can push aerosols into stratosphere • Aerosols can cool Earth for a year or more • e.g. Tambora → year without a summer, 1816 • Top of stratosphere is where warming stops • Called Stratopause

20. Mesosphere & Thermosphere • Mesosphere is above stratopause • Cools with greater altitude until mesopause • Thermosphere is above mesopause • Warms with greater altitude • Density of atmosphere very thin here, little energy

21. Ionosphere • 60-400km in altitude • Contains electrically charged atoms & molecules • These particles called Ions • Creates global electrical and magnetic fields • One outcome of Ionosphere is Aurora Borealis (Northern lights) • Ionospere also can cause communication disruptions

22. Ozone in the Upper Atmosphere • Ozone (O3) – form of oxygen • Mostly in stratosphere, 14-50 km above surface • Absorbs ultraviolet radiation, protecting Earth • Normal reaction: • UV radiation absorbed by O3 • O3 splits into O2 and O • O2 and O reform into ozone (O3)

23. Ozone in the Upper Atmosphere • Ozone concentrations hurt by presence of CFCs • CFCs - synthetic chemicals used as refrigerant • They migrate from surface into upper atmosphere • Deplete ozone as Chlorine (Cl) attacks O3 molecules • UV radiation strikes CFC molecule • Cl atom released, attacks O3 molecule • O2 and ClO are the result • ClO joins with free oxygen (O) • O2 and Cl are the result • O2 cannot stop UV radiation • Cl attacks another O3 (step 2) • One Cl can eliminate many O3 molecules

24. Ozone in the Upper Atmosphere • Obvious “hole” in ozone appeared in 1980s • 1987 agreement to replace CFCs successful • Most CFCs have been phased out • Highest CFC concentration in 1997 • Since 1997 concentration has decreased • CFC molecules very stable, hard to break down • Several decades for CFCs to disappear

25. Ozone in the Lower Atmosphere • O3 is a pollutant near Earth’s surface • Harmful to human lung tissue • Does not protect from UV radiation • Formed by: • organic chemicals • nitrogen/oxygen molecules from burning • sunlight • So, most prevalent in cities during summer

26. A few more words about Aerosols – tiny airborne liquid or solid particles

27. Brown Clouds • These are essentially smog due to human activity • Stoves • Cooking fires • Two effects • Absorb solar radiation and heat lower atm (2-3 km altitude) • Blocks Sunlight producing ground cooling • May effect the monsoons

28. Brown Clouds • This is not just a problem in Asia or China • What do you know about the 1952 London Smog? • December 5-9 • The fog there was so thick that people could not see their own feet! • About 4,000 people died (maybe as many as 12,000)

30. Global Dimming • Because of aerosols pollution, the brightness of the Earth's surface has dropped about 7% • This probably represents a net cooling due to more sunlight being reflected by the increased particle load in the atmosphere

32. The US embassy in Beijing regularly posts automated air quality measurements at @beijingair on Twitter. On 18 November 2010, the feed described the PM2.5 measurement as "crazy bad" after registering a reading in excess of 500 for the first time. This description was later changed to "beyond index",a level which recurred in February, October, and December 2011 (also 1-19-2012 at 558)

37. How does the system maintain balance? • Chemical weathering (sink) and Volcanism (source) • Water and CO2 interact with silicate rock….weathering into clays, calcium carbonate • CaSiO3 + H2CO2 CaCo3 + SiO2 + H2O

38. Weathering • The rate of weathering is controlled by a bunch of factors. • Temperature: Reactions are quicker the hotter it is, so roughly double for every 10C of temp change. • Precip: more water, more carbonic acid • Veg: Planets enhance carbonic acid and break down rocks (increases rates 2-10 times)

39. Tectonic Control of CO2 • Remember from our discussion of sources and sinks of CO2 about the only (natural) way to get CO2 out of the ground is volcanism.

40. Tectonic Control of CO2: Uplift • Tectonics can also increase weathering • Uplift causes all sorts of processes that increase weathering • Glaciers • Mass Wasting • Enhanced rainfall

43. This becomes a functional feedback loop. • Warm conditions speed the removal of CO2 leading to reduced warming. • Cool conditions slow the removal, leading to reducing cooling.

44. Volcanism is the flip side of weathering

45. But the rates of volcanism vary a lot

46. Again, CO2 acts as a planetary thermostat through tectonic feedback loops. • Fast spreading increases CO2 with leads to greater weathering and faster CO2 removal. • Slow spreading reduces CO2 input, but leads to cool conditions that reduce weathering, leading to reduced cooling.

47. Broken thermostat? • Around 650-800 Myr there is evidence of ice sheets near the equator