Managing the Atmosphere: Acid Deposition

• The notes cover Unit #7, which focuses on managing the atmosphere
• The topics include acid deposition, photochemical smog, managing air pollution, and ozone depletion

Acid Deposition

• Acid deposition involves air pollutants depositing from the atmosphere as acidic wet deposition (pH < 5.6) or acidic dry deposition
• Primary pollutants come directly from a source, like sulfur dioxide from burning coal
• Secondary pollutants result from primary pollutants reacting with other chemicals, such as smog, sulfuric acid, and nitric acid
• Wet deposition includes snow, rain, hail, and fog
• Sulfuric and nitric acid are secondary pollutants that fall far from the source
• Dry deposition includes dust and gases

Steps of Acid Rain Formation

• Fossil fuels contain sulfur compounds
• Combustion of fossil fuels releases sulfur dioxide gas
• Nitrogen from the atmosphere reacts with oxygen in high temperatures of vehicle engines, forming nitrogen monoxide gas
• Nitrogen monoxide gas is released in vehicle emissions
• Sulfur dioxide gas reacts with water and oxygen in the atmosphere to form

Impacts of Acid Deposition

• Aquatic organisms: kills larva of fish, mollusks, and amphibians and negatively affects organisms relying on these for food and affects morphology of fish gills
• Vegetation and crops: damages chloroplasts, reduces photosynthesis, changes soil chemistry (reducing plant productivity), causes defoliation of crops and trees, and reduces crop yield
• Stone and brick buildings: erodes stone buildings, corrodes cars, enhances chemical weathering, erases writing on tombstones, and damages roads

Acid Deposition Prevention Strategies

• Renewable energy sources like wind, solar, geothermal, and hydropower
• Increase public transportation and limit vehicles, especially in urban areas
• Drive less by walking, biking, or carpooling
• Legislation, such as the Clean Air Act (1990), established emissions trading programs for sulfur dioxide
• Industrial smoke stalks should use scrubbers to chemically convert or physically remove pollutants
• Cars should use cleaner-burning engines and catalytic converters
• Implement permit trading programs and clean coal technologies

Photochemical Smog

• Photochemical smog is a mixture of air pollutants and particulates, including ground-level ozone, formed when oxides of nitrogen and volatile organic compounds are oxidized

Sources of Photochemical Smog

• Nitrogen oxides (NOx) come from car exhaust
• Volatile organic compounds (VOCs) come from vegetation (coniferous trees), paint, gas stations, gas exhaust (transportation), and plastic factories

Impacts of Photochemical Smog

• Causes eye and respiratory irritation, lung damage/cancer, and can trigger asthma attacks
• Decreases crop yields and deteriorates plastics and rubber
• Reduces visibility, negatively impacting transportation

Managing Air Pollution Strategies

• Reduce fossil fuel use
• Reduce sulfur dioxide emissions using flue gas desulfurization (scrubbers) and fuel desulfurization
• Reduce oxides of nitrogen emissions using catalytic converters
• Reduce particulates using electrostatic precipitators
• Manage volatile organic compounds (VOCs) through safe usage, storage, and disposal of household products
• Restrict vehicle use in urban areas
• Enforce legislation like the Clean Air Act and the Polluter Pays principle

Ozone Depletion

• Ozone concentration is measured using the Dobson Unit, with less than 100 DU considered an ozone hole

Causes of Ozone Depletion

• Release of synthetic chemicals, chlorofluorocarbons (CFCs) from refrigerants, solvents, and foam-forming agents

Steps in Ozone Depletion

• CFCs from aerosols and refrigerants are unreactive and don't break down in the troposphere
• CFCs move to the stratosphere and break down under ultraviolet light, releasing chlorine atoms
• Chlorine atoms rapidly react with ozone, breaking down ozone (O3) into oxygen (O2), causing ozone depletion
• Chlorine atoms remain in the stratosphere and continue to destroy ozone, represented by the equation: Cl + O3 -> ClO + O2

Impacts of Ozone Depletion

• Human health: eye cataracts and skin cancer
• Agriculture: reduced crop yield
• Biodiversity: UV damages chloroplasts, reduces plant productivity, reduction in phytoplankton, reduces aquatic productivity
• Economy: degradation of materials used in construction and clothing

Ozone Depletion over Antarctica

• Polar stratospheric clouds form due to very low temperatures over Antarctica
• Strong winds create a polar vortex, isolating stratospheric air during winter months

Alternatives to Ozone-Depleting Substances

• Hydrochlorofluorocarbons (HCFCs): have only 2 chlorine atoms (vs. 3 in CFCs), have a shorter lifespan, are less stable, and deplete the ozone layer less than CFCs and used as refrigerants and for making plastic foams, producing refrigerators, and freezers
• Fluorinated gases (F-gases): deliver no chlorine to the stratosphere, but absorb infrared radiation, contribute to global warming, are potent and long-lasting greenhouse gases (up to 23,000 times greater than carbon dioxide), and are used in refrigeration, air-conditioning, heat pumps, as blowing agents, solvents, and in fire extinguishers and aerosols

International Agreements to Reduce Ozone Depletion

• Vienna Convention for the Protection of the Ozone Layer: promotes cooperation by exchanging information on the effects of human activities on the ozone layer (research)
• Montreal Protocol on Substances that Deplete the Ozone Layer: global agreement to protect the ozone layer by phasing out ozone-depleting chemicals

Ozone Destruction Hypothesis (Rowland-Molina)

• Rowland and Molina hypothesized that CFCs are responsible for stratospheric ozone destruction
• Initially not accepted, further research and data collection confirmed the hypothesis that CFCs deplete ozone