Unit 7 - Managing the atmosphere

What is acid deposition?

What is acid deposition?

mix of air pollutants that deposit from the atmosphere as acidic wet deposition (with a pH <5.6) or acidic dry deposition

What is wet deposition?

acid rain (e.g. snow, rain, hail, fog)

What is dry deposition?

dust & gases

• Washed off by rain → acidic water that harms plants + wildlife

Why is acid deposition a global problem?

Wind can blow pollutants long distances → air pollution

How does acid deposition form?

1. fossil fuels contain sulfur compounds

2. combustion of fossil fuels releases sulfur dioxide gas

3. sulfur dioxide gas reacts with water and oxygen in the atmosphere to form sulfuric acid

4. nitrogen from the atmosphere reacts with oxygen in the high temperatures of vehicle engines to form nitrogen monoxide gas

5. nitrogen monoxide gas is released into the atmosphere in vehicle emissions

6. nitrogen monoxide gas reacts with oxygen and water in the atmosphere to form nitric acid

What creates the most acid deposition?

Coal-burning power stations created the most acid deposition

What are some impacts of acid deposition on marine ecosystems?:

• Low pH → kills fish + their larvae

• Damages fish gills → decline in fish population

• Disrupts food webs

What are some impacts of acid deposition on plants?:

• Defoliation of vegetation

• Acidic fog coats vegetation → reduced photosynthesis (reduces productivity)

• Decrease crop yield

What are some impacts of acid deposition on stone + brick buildings?:

enhanced chemical weathering (e.g. can dissolve limestone)

What is photochemical smog?

mixture of air pollutants and particulates, including ground level ozone, that is formed when oxides of nitrogen and VOCs react in the presence of sunlight

• More often in sunlight

• Ex. of secondary pollutant: ground-level ozone → formed b/t chemical reactions with NOx and VOCs

What are particulates?

solid particles and liquid droplets in the air — often from burning/dust-generating activities

What are VOCs?

VOCs: high vapor pressure + low water solubility; emitted as gases from certain solids or liquids (e.g. paints, paint strippers, cleaning supplies, & pesticides)

• Can cause: headaches, cancer, damage to the liver & kidneys

What are some impacts of photochemical smog?

• eye and respiratory irritation: can harm vision (inflammation + dry eyes) + lead to illness (e.g. lung cancer + asthma)

• decreased crop yields: reduces photosynthesis → blocks sunlight + pollutant can damage/yellow plant leaves

• deterioration of plastics and rubber → particles + dust stick to these surfaces

  • Acidic atmospheric accelerate the decay of these materials (esp. in humid environments)

How does reduced use of fossil fuels manage air pollution?

• lack of emissions (e.g. SO2) means production of clean energy doesn’t add to the acid deposition problem

How does reducing emissions of SO2 manage air pollution?

• Flue-gas desulfurisation (FGD): remove SO2 from exhaust emissions of fossil-fuel-powered stations

• Fuel desulfurisation: remove sulfur from a fuel source before it’s burnt

  • e.g) Coal washing & low-sulfur fuels

How does reducing emissions of NOx manage air pollution?

Catalytic converters

• lower emissions from exhaust systems in vehicles; reduce air pollution

How does reducing emissions of particulates manage air pollution?

electrostatic precipitators

• use electric charge to remove particulates from gases emitted in industrial smoke

How does reducing emissions of VOCs manage air pollution?

safe usage (e.g. increased ventilation when using products with VOCs), not storing open containers of VOCs, disposing of empty containers safely

How does restricting vehicle use in urban areas manage air pollution?

• fewer vehicles → reduced air pollution

  • Congestion charging: people using public transportation because it’s cheaper

How does legislation manage air pollution?

• “Polluter pays principle”: polluter is responsible for reducing/preventing it

• e.g) 1979 Geneva Convention that created framework for reducing acid deposition + air pollution in Europe

• e.g) Clean Air Act of 1970: permanent limits on SO2 and NOx emission in the U.S.

What is ozone concentration measured in?

The Dobson unit

What is an ozone hole?

an area where the average concentration of ozone is below 100 Dobson Units

What are CFCs?

chemical compounds that speed up the breakdown of ozone

• e.g) refrigerants & solvents

How does ozone depletion occur?

• CFCs from aerosols & refrigerants are unreactive compounds and aren’t broken down in the troposphere

• CFCs move into the stratosphere and break down in the presence of UV light to release a chlorine atom

• rapid reactions between chlorine atoms and ozone breaks down ozone (O3) to oxygen (O2), causing ozone depletion

• chlorine atoms remain in the stratosphere and can continue to destroy ozone

Why is there major ozone depletion in Antarctica?

• Due to atmospheric conditions in Antarctica

• Ozone-depleting substances are transported great distances by wind

• Very low temperatures for a long period of time → PSCs - stratospheric clouds that form over the poles in winter

• Chemical reactions on liquids + solids increase abundance of chlorine, which reacts with ozone & creates the ozone hole over Antarctica

What is a polar vortex?

large, long-lasting rotating low-pressure system located over the North and South Poles; strengthens winters

• Chlorine gases persist for a long time & damage the ozone layer

How does ozone depletion impact human health?

skin cancer, formation of cataracts, & immune system suppression

How does ozone depletion decrease crop yields?

impacts how plants form + utilize nutrients → damages growth, which can harm biodiversity

How does ozone depletion impact marine biodiversity?

decreased #s of phytoplankton & can harm early developmental stages of many marine organisms

How does ozone depletion impact degradation of materials?

clothing and construction: lose strength, crack, & disintegrate

What are HCFCs?

Less stable + harmful than CFCs

• Depletes ozone at slow rate and shorter period of time

What are F-gases?

least harmful to ozones, but strong GHGs (add to greenhouse effect)

What’s the Rowland-Molina hypothesis?

CFCs could reach the stratosphere where they’d release chlorine atoms due to UV radiation

Why wasn’t the Roland-Molina hypothesis initially supported?

• Originally based on other hypothesis, not experimental data

• Resistance from industries producing CFCs

• Auxiliary hypotheses were backed by data

What’s Montreal Protocol?

50% reduction of CFC use by 2000; negotiated by 24 countries & resulted in heavy financial burdens if failed

• Further expanded in recent years (e.g. limiting the amount of F-gases)