First stageDepartment of Environmental Health Environmental pollution Lec

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First stage/Department of Environmental Health Environmental pollution Lec 3 Stratospheric Ozone Formation & Depletion

First stage/Department of Environmental Health Environmental pollution Lec 3 Stratospheric Ozone Formation & Depletion Mohammed Al-Jawasim

What is OZONE? • Ozone (O 3): is a gas composed of three atoms

What is OZONE? • Ozone (O 3): is a gas composed of three atoms of oxygen. • Bluish gas that is harmful to breathe • Nearly 90% of the Earth's ozone is in the stratosphere and is referred to as the ozone layer • Ozone absorbs a band of ultraviolet radiation called UVB

The stratosphere • Stratosphere is about 10, 000 m to 49, 000 m •

The stratosphere • Stratosphere is about 10, 000 m to 49, 000 m • Temperatures about -50 o. C until 30, 000 m and then increase to about 23 o. C. Increase due to absorption of UV by ozone/oxygen. • Ozone protects earth surface from UV rays.

The ultraviolet spectrum 400 nm Radio IR Visible Light 100 nm UV X-Rays q

The ultraviolet spectrum 400 nm Radio IR Visible Light 100 nm UV X-Rays q UV light: 100 to 400 nm UV spectrum – 4 regions o Far UV: 100 – 200 nm l UV-A UV-B UV-C Far UV o UV – C : 200 – 280 nm o UV – B : 280 – 315 nm o UV – A : 315 – 400 nm 300 nm 200 nm DNA damaging range

UV Radiation • 230 -280 nm damages nucleic acids • Stops reproduction of cells

UV Radiation • 230 -280 nm damages nucleic acids • Stops reproduction of cells by breaking apart the DNA bonds. • Ozone production peaks at 185 nm • Ozone absorbance and destruction at 200320 nm.

Ozone Formation/Destruction in the Stratosphere

Ozone Formation/Destruction in the Stratosphere

Ozone depletion • World-wide monitoring shows stratospheric ozone decreasing for more than two decades.

Ozone depletion • World-wide monitoring shows stratospheric ozone decreasing for more than two decades. • Since the 1970 s, an ozone hole has formed over Antarctica in which up to 60 % of the total ozone is depleted.

Ozone-Depleting Substance(s) (ODS): • Chloro. Fluoro. Carbons CFCs, • Hydrochlorofluorocarbons HCFCs, • • halons,

Ozone-Depleting Substance(s) (ODS): • Chloro. Fluoro. Carbons CFCs, • Hydrochlorofluorocarbons HCFCs, • • halons, methyl bromide, carbon tetrachloride, and methyl chloroform.

Chlorofluorocarbons (CFCs). • Depletion of ozone primarily due to Chloro. Fluoro. Carbons (CFCs). •

Chlorofluorocarbons (CFCs). • Depletion of ozone primarily due to Chloro. Fluoro. Carbons (CFCs). • CFCs are commonly used as refrigerants, solvents, and foam blowing agents. • The most common CFCs are CFC-11, CFC-12, CFC 113, CFC-114, and CFC 115.

How do CFCs affect ozone? • CFCs - unreactive in the troposphere and move

How do CFCs affect ozone? • CFCs - unreactive in the troposphere and move unchanged to stratosphere • Short-wave UV light in stratosphere breaks down CFCs and chlorine is released • Much of the chlorine reacts to form HCl or other compounds that do not react with ozone Ø Cl + O 3 Cl. O + O 2 Ø Cl. O + O Cl + O 2 Ø Cl. O + Cl. O Cl 2 O 2 Cl 2 + O 2 Ø Cl 2 can photodissociate to form more chlorine atoms

“A single chlorine atom can destroy as many as 100, 000 ozone molecules during

“A single chlorine atom can destroy as many as 100, 000 ozone molecules during residence in stratosphere”

Ozone-Depleting Substances (ODS) • Freon 11 is fluorodichloromethane and has a structure of CCl

Ozone-Depleting Substances (ODS) • Freon 11 is fluorodichloromethane and has a structure of CCl 3 F • Carbon tetrachloride, methyl bromide and methyl chloroform and other halons also destroy the ozone layer

Effects of ODS 1. Increase UV radiation 2. -- Skin Cancer (melanoma and nonmelanoma)

Effects of ODS 1. Increase UV radiation 2. -- Skin Cancer (melanoma and nonmelanoma) 3. Premature aging of the skin and other skin problems 4. Cataracts and other eye damage 5. Immune system suppression 6. damage to crops, damage to • Picture shows marine organisms (like reefs), squamous cell damage to plastics carcinoma in elderly patient

The ozone depleting potential • The ozone depleting potential (ODP) is the ratio of

The ozone depleting potential • The ozone depleting potential (ODP) is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of (trichliorflouromethane) CFC-11. • Thus, the ODP of CFC-11 is defined to be 1. 0. • HFCs have zero ODP? because they do not contain chlorine. • Other CFCs and HCFCs have ODPs that range from 0. 01 to 1. 0. • The halons have ODPs ranging up to 10. • Carbon tetrachloride has an ODP of 1. 2, and methyl chloroform's ODP is 0. 11.

CFC characteristics

CFC characteristics

Ozone hole • The ozone hole is the region over Antarctica with total ozone

Ozone hole • The ozone hole is the region over Antarctica with total ozone 220 Dobson Units or lower. (The average total column ozone in the atmosphere is about 300 DU. )

Montreal Protocol • 1989 Global Treaty to protect ozone layer • Currently 140 countries

Montreal Protocol • 1989 Global Treaty to protect ozone layer • Currently 140 countries are parties • Timetable to reduce and end production and consumption of 8 major halocarbons • Many governments committed to early phase outs.

Montreal Protocol – The Montreal Protocol was signed in 1987 by 46 countries, including

Montreal Protocol – The Montreal Protocol was signed in 1987 by 46 countries, including the US. – It entered into force in 1989. – By 1996, developed countries phased out use of CFCs, halons and CCl 4; developing countries have until 2010. – Developed countries are scheduled to phase out production of HCFCs by 2030; developing countries have until 2040.

References • Hill, M. K. 2010. Understanding environmental pollution. 3 rd Edition. Cambridge University

References • Hill, M. K. 2010. Understanding environmental pollution. 3 rd Edition. Cambridge University Press. • Raven H. P. &Berg R. L. 2005. Environment. 5 th edition. United States of America: Wiley PLUS.