atmospheric ozone: facts and misconceptions
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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 PresentationTRANSCRIPT
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Arthur N. SamelChair, Department of GeographyBowling Green State University
&Chief Reader,
Advanced Placement Environmental Science Program
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The concentration of O3 near the earth’s surface is minute ~40 ppb
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Location of stratospheric O3
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Atmospheric O3 concentration as a function of height/altitude
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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
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CFCs…
Oh NO!!!
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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.
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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
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What is a greenhouse gas? Transparent to insolation Absorbs outgoing terrestrial radiation
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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?
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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
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DU = thickness of compressed atmospheric O3 at 0°C * 100.(e.g., 4mm = 400 DU)
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Bar graph of area with Antarctic low O3 concentrations (< 220 DU) during Octoberand November (area of North America ~ 24 million km2).
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Monthly average total O3 Northern Hemisphere spring
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Bar graph of area with Arctic low O3 concentrations (< 300 DU) during Februaryand March.
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Increased rate of skin cancers
Increased frequency of cataracts
Decreased phytoplankton productivity
Decreased photosynthesis rates
Decreased plant growth rates
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Atmospheric O3 concentration as a function of height/altitude
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NOx
VOCs
NOx Sources
Tropospheric Ozone Formation:2NO + O2 → 2NO2
NO2 + → NO + OO + O2 → O3
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Various sources of VOCs
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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].
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Variation in ground level O3 concentration during a typical 24-hour day
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New York City, July 10, 2007
New York City, July 16, 2008
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L.A. City Hall, 1953 L.A. City Hall, 2005
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Number of days when the 1-hour federal O3 standard was exceededin Los Angeles as well as the 1-hour peak concentration
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Is O3 an atmospheric greenhouse gas?
Does the formation of tropospheric O3
enhance the atmospheric greenhouse effect?
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Factors that contribute to atmospheric warming and cooling and our levelof understanding
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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
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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)