Global atmospheric change - chapter 11 - chemistry of the environment

Law of Unintended Consequences

The observation that actions taken to solve one environmental problem often have other effects which in many cases have a negative impact

greenhouse effect

• insulating effect of certain gases in the air which can lead to higher temperatures in the lower atmosphere

• Light can get in, but heat has trouble getting out

global warming

Gradual, general warming of the Earth's atmosphere believed to be caused by the increased emissions of certain gases

natural greenhouse gases

• water vapor

• carbon dioxide

• methane (CH4)

• nitrous oxide (N2O)

• ozone (O3)

manufactured greenhouse gases

chlorofluorocarbons (CFCs)

carbon dioxide

• product of burning coal, oil, and natural gas

• U.S. emissions are 18% of world

methane

• arises from:

  • solid waste decomposition

  • digestive tracts of livestock

  • coal mining

  • rice paddies

  • natural gas and petroleum production

• 21x more effective as a greenhouse gas than CO2

• concentration is less than 1% that of CO2

chlorofluorocarbons (CFCs)

• greenhouse gases

• many have leveled off and are declining

  • made illegal by international agreement bc of effect on ozone layer

• do not break down in lower atmosphere

  • eventually go to stratosphere where they are reactive

hydrochlorofluorocarbons (HCFCs)

• industry made substitute for CFCs

• hydrogen reacts with tropospheric hydroxyl (OH)

• shorter atmospheric lifetime

• contain chlorine

  • destroy stratospheric ozone

hydrofluorocarbons (HFCs)

• considered one of the best substitutes for reducing stratospheric ozone loss

• short lifetime

• lack of chlorine and bromine

• Still efficient greenhouse gases

Nitrous oxide

• colorless, sweet-tasting gas

• low concentration in atmosphere

  • no danger to humans

• Stable gas

• mostly produced by denitrifying bacteria that break down nitrogen-containing wastes

permafrost

Layer of soil, sediment, and/or rock that is permanently frozen

the ozone layer

• ozone in the stratosphere is naturally occurring

• O3 + UV → O2 + O

  • absorbs UV radiation to protect earth

  • free oxygen atom is very reactive

• O2 + O → O3 + heat

  • reacts quickly and energy from UV radiation produces heat

• These reactions involve high energy ultraviolet radiation (HEUV)

  • HEUV cleaves an oxygen molecule into two oxygen atoms

    • O2 + HEUV → 2O

  • These oxygen atoms can then react with oxygen molecules, creating ozone

    • O2 + O → O3 + heat

Montreal protocol

• signed by 57 countries, the parties agreed to cut their \n use of most CFCs by 50% by 1998

• poorer countries refused to sign

  • argued that they would not be able to afford to use the more expensive CFC substitutes

London Protocol

• meeting in 1990 to phase out all CFCs completely by 2000

• Developed countries agreed to pay into a temporary fund to help less-developed countries make the transition away from CFCs

• 93 countries signed the London Agreement