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)