2. OZONE LAYER AND PESTICIDES A PRESENTATION BY ALLAH DAD KHAN

3. WHAT IS THE OZONE LAYER? The ozone layerHelpozone layerThe region of the stratosphere containing the bulk of atmospheric ozone. The ozone layer lies approximately 15-40 kilometers (10-25 miles) above the Earth's surface, in the stratosphere. Depletion of this layer by ozone depleting substances (ODS) will lead to higher UVB levels, which in turn will cause increased skin cancers and cataracts and potential damage to some marine organisms, plants, and plastics. The science page (http://www.epa.gov/ozone/science/index.html) offers much more detail on the science of ozone depletion. is a concentration of ozone molecules in the stratosphereHelpstratosphereThe region of the atmosphere above the troposphere. The stratosphere extends from about 10km to about 50km in altitude. Commercial airlines fly in the lower stratosphere. The stratosphere gets warmer at higher altitudes. In fact, this warming is caused by ozone absorbing ultraviolet radiation. Warm air remains in the upper stratosphere, and cool air remains lower, so there is much less vertical mixing in this region than in the troposphere.. About 90 percent of the planet's ozone is in the ozone layer. The layer of the Earth's atmosphere that surrounds us is called the troposphereHelptroposphereThe region of the atmosphere closest to the Earth. The troposphere extends from the surface up to about 10 km in altitude, although this height varies with latitude. Almost all weather takes place in the troposphere. Mt. Everest, the highest mountain on Earth, is only 8.8 km high. Temperatures decrease with altitude in the troposphere. As warm air rises, it cools, falling back to Earth. This process, known as convection, means there are huge air movements that mix the troposphere very efficiently.. The stratosphere, the next higher layer, extends about 6 to 31 miles (or 10 to 50 kilometers) above the Earth's surface.

4. WHY IS THE OZONE LAYER IMPORTANT? Stratospheric ozone is a naturally occurring gas that filters the sun's ultraviolet (UVHelpUVUltraviolet radiation is a portion of the electromagnetic spectrum with wavelengths shorter than visible light. The sun produces UV, which is commonly split into three bands: UVA, UVB, and UVC. UVA is not absorbed by ozone. UVB is mostly absorbed by ozone, although some reaches the Earth. UVC is completely absorbed by ozone and normal oxygen. can lead to skin cancer, cataracts, and weakened immune systems. Increased UV can also lead to reduced crop yield and disruptions

5. METHYL BROMIDE AND OZONE Methyl bromide, an odorless, colorless gas used as an agricultural pesticide, was introduced in the 1980s as an effective way to control weeds and increase fruit yields. Agricultural production nurseries around the world relied on methyl bromide (MB) to produce healthy plants for export and domestic sales. In 2000, the widely used pesticide was classified as an ozone-depleting substance, and in 2005 MB was banned in the United States and all European Union countries.

6. NEW TOXIC PESTICIDES New Toxic Pesticides to Replace Older Ozone Depleting Pesticides.... Methyl Bromide, a soil fumigant often used on strawberry crops, was phased out in the US by 2005 because it was depleting the ozone layer. The phase out was based on the Montreal Protocol on Substances that Deplete the Ozone Layer and the Clean Air Act.

7. WHICH CHEMICAL IS RESPONSIBLE FOR OZONE LAYER DEPLETION? Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances(ODS) are mainly responsible for man-made chemical ozone depletion. The total amount of effective halogens (chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine (EESC). Methyl bromide is a toxic substance. Human exposure to high concentrations of methyl bromide can cause central nervous system and respiratory system failures and can harm the lungs, eyes, and skin.

8. WHAT CAUSES OZONE LAYER DEPLETION? Ozone depletion occurs when chlorofluorocarbons (CFCs) and halons—gases formerly found in aerosol spray cans and refrigerants—are released into the atmosphere (see details below).... CFCs and halons cause chemical reactions that break down ozone molecules, reducing ozone's ultraviolet radiation-absorbing capacity.

9. WHAT CAUSES OZONE LAYER DEPLETION Some of the pesticides contain hazardous materials such as DDT, of which when applied can not be easily degraded by natural process, they can travel long distance and remain to the atmosphere for long time, hence can attach themselves to the ozone layer and depleting it, result to ozone layer depletion

10. MONTREAL PROTOCOL The Montreal protocol was set up in 1987 to eliminate chemicals that damage the ozone layer. It has been hugely successful in phasing out chlorofluorocarbons (CFCs), while the pesticide methyl bromide, the last major ozone-depleting chemical still in use, was due to be phased out by the end of 2004. But US strawberry and tomato farmers, who fumigate crops with methyl bromide, have stuck a spanner in the works.

11. CHLOROFLUOROCARBONS (CFCs) are anthropogenic compounds that have been released into the atmosphere since the 1930s in various applications such as in air- conditioning, refrigeration, blowing agents in foams, insulations and packing materials, propellants in aerosol cans, and as solvents. Chlorofluorocarbons, commonly known as CFCs, are a group of man-made... the Sun, releasing free chlorine atoms which cause significant ozone depletion. These substances all release chlorine atoms into the stratosphere. A single chlorine atom can break apart more than 100,000 ozone molecules

12. Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for 40-150 years, and concentrations can be expected to reach 10 to 30 times present levels. Photodissociation of the chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone.”

13. WILL THE OZONE LAYER RECOVER? The ozone layer is expected to return to normal levels by about 2050. But, it is very important that the world comply with the Montreal Protocol; delays in ending production and use of ozone-depleting substances could cause additional damage to the ozone layer and prolong its recovery.