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

Atmospheric O 3 concentration as a function of height/altitude

Stratospheric Ozone “Cycle” : 2O 3 + → 2O 2 + O ( < 290 nm; UV-B; 90% absorption) 2O 2 + 2O → 2O 3 O 2 + → 2O ( < 240 nm; UV-C; 100% absorption) 2O + O 2 → 2O 3

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) O 3 + → O 2 + O ( < 290 nm; UV-B) Cl + O 3 → ClO + O 2 ClO + O → Cl + O 2 A single Cl - radical can reside in the stratosphere for nearly a decade and disrupt the formation of several hundred thousand O 3 molecules. Increased UV-B reached Earth’s surface

 What is a greenhouse gas ?  Transparent to insolation  Absorbs outgoing terrestrial radiation

 Is O 3 an atmospheric greenhouse gas?  How can the destruction of stratospheric O 3 enhance the atmospheric greenhouse effect?  Does the destruction of stratospheric O 3 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 O 3 at 0°C * 100. (e.g., 4mm = 400 DU)

Bar graph of area with Antarctic low O 3 concentrations (< 220 DU) during October and November (area of North America ~ 24 million km 2).

Monthly average total O 3 Northern Hemisphere spring

Bar graph of area with Arctic low O 3 concentrations (< 300 DU) during February and March.

 Increased rate of skin cancers  Increased frequency of cataracts  Decreased phytoplankton productivity  Decreased photosynthesis rates  Decreased plant growth rates

Atmospheric O 3 concentration as a function of height/altitude

NOx VOCs NO x Sources Tropospheric Ozone Formation : 2NO + O 2 → 2NO 2 NO 2 + → NO + O O + O 2 → 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 NO 2 (through reaction with HO 2 or RO 2 radicals), which also regenerates OH [ R3, R4 ]. NO 2 is photolyzed to generate atomic oxygen, which combines with O 2 to create O 3 [ 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 O 3 standard was exceeded in Los Angeles as well as the 1-hour peak concentration

 Is O 3 an atmospheric greenhouse gas?  Does the formation of tropospheric O 3 enhance the atmospheric greenhouse effect?

Factors that contribute to atmospheric warming and cooling and our level of understanding

Global Warming Potentials (GWP) and Atmospheric Lifetimes (Years) Used in the Inventory Gas Atmospheric Lifetime 100-year GWPa 20-year GWP 500-year GWP Carbon dioxide (CO 2 ) Methane (CH 4 )b 12± Nitrous oxide (N 2 O) HFC ,700 9,100 9,800 HFC ,800 4, HFC-134a ,300 3, HFC-143a ,800 5,000 1,400 HFC-152a HFC-227ea ,900 4, HFC-236fa 209 6,300 5,100 4,700 HFC-4310mee ,300 3, CF 4 50,000 6,500 4,400 10,000 C 2 F 6 10,000 9,200 6,200 14,000 C 4 F 10 2,600 7,000 4,800 10,100 C 6 F 14 3,200 7,400 5,000 10,700 SF 6 3,200 23,900 16,300 34,900

Net 100-year Global Warming Potentials for Select Ozone Depleting Substances Gas Direct Netmin Netmax CFC-11 4,600 (600) 3,600 CFC-12 10,600 7,300 9,900 CFC-113 6,000 2,200 5,200 HCFC-22 1,700 1,400 1,700 HCFC HCFC HCFC-141b 700 (5) 570 HCFC-142b 2,400 1,900 2,300 CHCl (560) 0 CCl 4 1,800 (3,900) 660 CH 3 Br 5 (2,600) (500) Halon ,300 (24,000) (3,600) Halon ,900 (76,000) (9,300)