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Atmospheric Ozone: Facts and Misconceptions. Arthur N. Samel Chair, Department of Geography Bowling Green State University & Chief Reader, Advanced Placement Environmental Science Program. The concentration of O 3 near the earth’s surface is minute ~40 ppb. Location of stratospheric O 3. - PowerPoint PPT Presentation
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Arthur N. SamelChair, Department of GeographyBowling Green State University
&Chief Reader,
Advanced Placement Environmental Science Program
The concentration of O3 near the earth’s surface is minute ~40 ppb
Location of stratospheric O3
Atmospheric O3 concentration as a function of height/altitude
Stratospheric Ozone “Cycle”:
2O3 + → 2O2 + O ( < 290 nm; UV-B; 90% absorption)2O2 + 2O → 2O3
O2 + → 2O ( < 240 nm; UV-C; 100% absorption)2O + O2 → 2O3
CFCs…
Oh NO!!!
CFCs are extremely stable molecules in the troposphere and become well mixed.
It takes many years (60-100) for CFC molecules to enter the stratosphere.
Once in the stratosphere, CFCs absorb UV-C radiation, dissociate, and Cl- radicals are released.
Stratospheric Ozone Destruction: CFCs
CFC + → CFC + Cl ( < 215 nm; UV-C)O3 + → O2 + O ( < 290 nm; UV-B)Cl + O3 → ClO + O2
ClO + O → Cl + O2
A single Cl- radical can reside in the stratosphere for nearly a decade and disrupt the formation of several
hundred thousand O3 molecules.
Increased UV-B reached Earth’s surface
What is a greenhouse gas? Transparent to insolation Absorbs outgoing terrestrial radiation
Is O3 an atmospheric greenhouse gas?
How can the destruction of stratospheric O3 enhance the atmospheric greenhouse
effect?
Does the destruction of stratospheric O3
contribute to warming in the troposphere?
Energy emission spectra of Sun and Earth (A) and absorption of energy in the Earth’s atmosphere (B).
UV-B absorption in the stratosphereIR absorption in the troposphere
DU = thickness of compressed atmospheric O3 at 0°C * 100.(e.g., 4mm = 400 DU)
Bar graph of area with Antarctic low O3 concentrations (< 220 DU) during Octoberand November (area of North America ~ 24 million km2).
Monthly average total O3 Northern Hemisphere spring
Bar graph of area with Arctic low O3 concentrations (< 300 DU) during Februaryand March.
Increased rate of skin cancers
Increased frequency of cataracts
Decreased phytoplankton productivity
Decreased photosynthesis rates
Decreased plant growth rates
Atmospheric O3 concentration as a function of height/altitude
NOx
VOCs
NOx Sources
Tropospheric Ozone Formation:2NO + O2 → 2NO2
NO2 + → NO + OO + O2 → O3
Various sources of VOCs
Ozone formation occurs through the following sequence of reactions. The sequence is almost always initiated by the reaction of various VOC or CO with the OH radical [R1, R2]. This is followed by the conversion of NO to NO2 (through reaction with HO2 or RO2 radicals), which also regenerates OH [R3, R4]. NO2 is photolyzed to generate atomic oxygen, which combines with O2 to create O3 [R5, R6].
Variation in ground level O3 concentration during a typical 24-hour day
New York City, July 10, 2007
New York City, July 16, 2008
L.A. City Hall, 1953 L.A. City Hall, 2005
Number of days when the 1-hour federal O3 standard was exceededin Los Angeles as well as the 1-hour peak concentration
Is O3 an atmospheric greenhouse gas?
Does the formation of tropospheric O3
enhance the atmospheric greenhouse effect?
Factors that contribute to atmospheric warming and cooling and our levelof understanding
Global Warming Potentials (GWP) and Atmospheric Lifetimes (Years) Used in the Inventory
Gas Atmospheric Lifetime 100-year GWPa 20-year GWP 500-year GWPCarbon dioxide (CO2) 50-200 1 1 1Methane (CH4)b 12±3 21 56 6.5Nitrous oxide (N2O) 120 310 280 170HFC-23 264 11,700 9,100 9,800HFC-125 32.6 2,800 4,600 920HFC-134a 14.6 1,300 3,400 420HFC-143a 48.3 3,800 5,000 1,400HFC-152a 1.5 140 460 42HFC-227ea 36.5 2,900 4,300 950HFC-236fa 209 6,300 5,100 4,700HFC-4310mee 17.1 1,300 3,000 400CF4 50,000 6,500 4,400 10,000C2F6 10,000 9,200 6,200 14,000C4F10 2,600 7,000 4,800 10,100C6F14 3,200 7,400 5,000 10,700SF6 3,200 23,900 16,300 34,900
Net 100-year Global Warming Potentials for Select Ozone Depleting Substances
Gas Direct Netmin NetmaxCFC-11 4,600 (600) 3,600CFC-12 10,600 7,300 9,900CFC-113 6,000 2,200 5,200HCFC-22 1,700 1,400 1,700HCFC-123 120 20 100HCFC-124 620 480 590HCFC-141b 700 (5) 570HCFC-142b 2,400 1,900 2,300CHCl3 140 (560) 0CCl4 1,800 (3,900) 660CH3Br 5 (2,600) (500)Halon-1211 1,300 (24,000) (3,600)Halon-1301 6,900 (76,000) (9,300)