《环境化学》课程PPT教学课件讲稿（英文版）Unit 9 Stratospheric Ozone depletion

Stratospheric Ozone Depletion

Stratospheric Ozone Depletion

Ozone in the atmosphere STRATOSPHERE TROPOSPHERE In this region, ozone protects In this region, ozone can us from the sun's harmful damage lung tissue and uitraviolet radiation onts MESOSPHERE

Ozone in the atmosphere

The ozone layer Altitud Altitude 80 km Mesosphere 50 km Ozone stratosphere layer 10 km Tro asphere Temperature Czone concentration

The ozone layer

Ultraviolet protection by ozone of sunligh outside ozone layer After passage through ozone layer 400 60 Visible light: 400-700 nm Ultraviolet ligl Ozone absorbs UV light in the solar irradiation that is harmful to life

Ultraviolet protection by ozone Ozone absorbs UV light in the solar irradiation that is harmful to life

Ultraviolet protection by ozone 9 Relative Actual action sensitivity urn Ground-level radiation 60 6 好 3 2 270 280 320 33 0 340 Wavelength of Light(nm) The overlap of ground level radiation with the sunburn sensitivity curve would be much greater without the filtering effects of the ozone layer

Ultraviolet protection by ozone The overlap of ground level radiation with the sunburn sensitivity curve would be much greater without the filtering effects of the ozone layer

Express ozone abundance Total column ozone is the total amount of ozone integrated from the surface to the top of the atmosphere Dobson Units(DU is used to express the total column ozone, named after G.M.B. dobson. a scientist who conducted pioneering measurements of the stratosphere in the 1920s and 1930s One du is the thickness measured in units of hundredths of a millimeter(0.01 mm), that the ozone column would occupy at standard temperature and pressure(273 K and 1 atm

Express ozone abundance • Total column ozone is the total amount of ozone integrated from the surface to the top of the atmosphere. • Dobson Units (DU) is used to express the total column ozone, named after G.M.B. Dobson, a scientist who conducted pioneering measurements of the stratosphere in the 1920s and 1930s. • One DU is the thickness, measured in units of hundredths of a millimeter (0.01 mm), that the ozone column would occupy at standard temperature and pressure (273 K and 1 atm)

Typical ozone column values Total ozone column value ranges from 290 to 310 DU over the globe. If all the atmosphere' s ozone were brought down to the earth's surface at standard pressure and temperature, it would produce a layer of about 3mm thick Ozone depletion: when sum of ozone over height is lower than 2/3 of the normal value we say"ozone depletion " occurs

Typical ozone column values • Total ozone column value ranges from 290 to 310 DU over the globe. • If all the atmosphere's ozone were brought down to the earth's surface at standard pressure and temperature, it would produce a layer of about 3mm thick. • Ozone depletion: when sum of ozone over height is lower than 2/3 of the normal value, we say "ozone depletion" occurs

What is ozone? Ozone is a stable molecule O composed of three oxygen atoms While stable, it is highly reactive. The greek word ozein means to smell"and o3 has a strong pungent odor. Electric discharges in air often produce significant quantities of o3 and you may have smelled o3 near these sources

What is ozone? Ozone is a stable molecule composed of three oxygen atoms. O O O While stable, it is highly reactive. The Greek word ozein means “to smell” and O3 has a strong pungent odor. Electric discharges in air often produce significant quantities of O3 and you may have smelled O3 near these sources

Ozone formation and destruction in the stratosphere Oa Formation Photon= hu<242 nm Highly energetic oxygen atoms Oxygen Energy ● transfer b. High-energy oxygen atom (Low kinetic energy) CHigh kinetic energy. Stable ozone Highly energetic collision (M is a third body, for example n2, O Ou Destructi Photon=<(200-320nm) ozone Oxygen molecule Two-body collision Oxygen molecules

Ozone formation and destruction in the stratosphere

Chapman Theory )O2+hV(20 formation b)o+O2+M->O3+M c)O3+hv(202 Where M is a random air molecule(o2 or N2) Steady-state 03 03] kaki 1/2 concentration O2] kk Chapman theory describes how sunlight converts the various forms of oxygen from one to another, explains why the highest content of ozone occur in the layer between 15 and 50 km, termed the ozone layer

Chapman Theory a) O2+ hv ( 2O b) O+O2+M -> O3+M c) O3 + hv (<320nm)→ O +O2 d) O + O3→2O2 Where M is a random air molecule (O2 or N2) Chapman theory describes how sunlight converts the various forms of oxygen from one to another, explains why the highest content of ozone occur in the layer between 15 and 50 km, termed the ozone layer formation Destruction 1/ 2 ) [ ] ( [ 2] [ 3] c d a b k k k k M O O = Steady-state O3 concentration