Air Pollution and its Sources

Air Pollutants from Combustion

• Coal combustion emits carbon dioxide, sulfur dioxide, toxic metals, and particulate matter.
• Fossil fuel combustion releases nitrogen oxides, leading to ozone production, photochemical smog, nitric acid formation, acid rain, carbon monoxide, hydrocarbons, and particulate matter.
• Diesel fuel combustion releases sulfur dioxide, affecting air quality.
• The Clean Air Act (CAA), overseen by the Environmental Protection Agency (EPA), has regulated lead use, especially in fuels, significantly reducing atmospheric lead.
• Air pollutants can be categorized as primary or secondary.

Specific Air Pollutants and Their Impacts

• Sulfur Dioxide (SO2): From coal combustion, causes respiratory irritation, smog, and acid precipitation.
  • It worsens asthma and bronchitis.
  • Sulfur aerosols block sunlight, reducing visibility and forming sulfurous gray smog.
  • Combines with water and oxygen to form sulfuric acid, leading to acid precipitation.
• Nitrogen Oxides (NOx): From all fossil fuel combustion, contributes to ozone, photochemical smog, and acid precipitation.
  • Includes NO and NO2.
  • Nitrogen monoxide (NO) forms when nitrogen combines with oxygen, and sunlight converts NO2 back into NO.
  • Functions as a respiratory irritant, leading to tropospheric ozone and photochemical smog.
• Carbon Monoxide (CO): Results from incomplete combustion; lethal to humans.
• Particulate Matter (PM): From fossil fuels and biomass combustion; causes smog and respiratory irritation.
• Ozone (O3): Produced by photochemical oxidation of NO2; respiratory irritant, contributes to smog, and causes plant damage.
• Lead (Pb): From metal plants and waste incineration; a neurotoxicant.
  • Formerly common in gasoline, phased out by the EPA starting in 1974.
  • Catalytic converters are required to reduce emissions.

Carbon Dioxide (CO2)

• CO2 is not one of the six pollutants regulated by the CAA.
  • It does not directly lower air quality in terms of human health.
  • Neither toxic, damaging to lungs/eyes, nor does it lead to smog or visibility reduction.
• The CAA is a greenhouse gas that contributes to global warming, with environmental and human health consequences.
• Coal combustion releases more air pollutants than other fossil fuels, including CO, CO2, SO2, NOx, toxic metals, and PM.

Primary vs. Secondary Pollutants

• Primary Pollutants: Emitted directly from sources like vehicles, power plants, and natural sources; examples include NOx, CO, CO2, VOCs, SO2, and PM.
• Secondary Pollutants: Formed when primary pollutants transform in the presence of sunlight, water, and oxygen; more prevalent during the day due to sunlight. Examples include tropospheric ozone, sulfuric acid and sulfate, and nitric acid and nitrate.

Photochemical Smog

• It forms when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight.
• Environmental factors affect its formation.
• Nitrogen oxide is produced early in the day, and ozone peaks in the afternoon, especially in summer.
• VOCs, like gasoline and formaldehyde, evaporate at room temperature; trees are a natural source.
• Smog often concentrates in urban areas with high vehicle traffic.
• Reduction involves decreasing nitrogen oxide and VOCs causing respiratory issues and eye irritation.
• Sunlight breaks down NO2 into NO + O.
• VOCs bind with NO, forming photochemical oxidants.
• Ozone (O3) forms when NO2 is broken down by sunlight, and free O binds to O2.
• Higher VOC emissions, increased vehicle traffic (increasing NO2 emissions), and more sunlight increase smog formation.

Impacts and Reduction of Smog

• Reduces sunlight, limiting photosynthesis.
• Ozone damages plant stomata and irritates animal respiratory systems.
• Worsens asthma, irritates eyes, and causes respiratory irritation.
• Increasing healthcare costs, lost productivity due to sickness, and decreased agricultural yields result.
• Reducing vehicle use promotes carpooling, public transport, biking, and walking.
• Increase electricity production from renewables.

Thermal Inversion

• The normal temperature gradient in the atmosphere is altered as the air temperature at the earth's surface is cooler than the air at higher altitudes
• Pollutants become trapped near the ground as a result, especially smog and particulates
• Air convection carries air pollutants away from earth's surface and distributes them higher into the atmosphere
• Air pollutants trapped closer to earth(smog, PM, ozone, SO2, Nox)

Urban Heat Island Effect

• Urban areas tend to have higher surface and air temperatures than surrounding areas due to lower albedo (more solar energy absorption) and less evapotranspiration.
• Effects an increase in respiratory irritation and asthma flare-ups.

Natural Sources of Air Pollutants

• Lightning strikes convert N2 to NOx.
• Forest fires release CO2 and H2O vapor.
• Plants emit VOCs.
• Volcanoes release SO2, PM, CO, and NOx.
• All living things release CO2 through respiration.
• Sea salt, pollen, and forest fire ash lead to haze and visibility reduction.
• Aerobic decomposition releases CO2, while anaerobic decomposition releases methane.

Particulate Matter (PM)

• PM10 (dust, pollen, ash, mold) irritates the respiratory tract.
• PM2.5 (combustion particles, smaller dust) travels deep into the lungs, increasing the risk of chronic bronchitis and lung cancer.

Indoor Air Pollutants

• Carbon monoxide is an asphyxiant.
• Particulates include asbestos, dust, and smoke.
• Pollutants come from natural sources, human-made sources, and combustion.
• Natural sources are radon, mold, and dust.
• Human-made sources are insulation, VOCs (furniture, carpeting), and lead-based paints.
• Combustion sources are carbon monoxide, nitrogen oxides, sulfur dioxides, particulates, and tobacco smoke.
• Radon gas infiltrates homes through soil and groundwater, leading to lung cancer.

Air Pollution in Developing vs. Developed Countries

• Developing Countries:
  • Relies on wood, manure, and charcoal cause deforestation.
  • Combustion occurs indoors with poor ventilation, leading to high concentrations of pollutants (CO, PM, NOx, VOCs).
• Developed Countries:
  • Relies on commercial fuels through utilities.
  • Chemicals in products, adhesives in furniture, cleaning supplies, insulation, and lead paint are pollutants

Common Indoor Air Pollutants

• Particulates: Smoke, asbestos (dangerous when disturbed).
• Carbon Monoxide (CO):
  • From incomplete combustion; lethal to humans especially when poorly ventilated.
• VOCs: Chemicals from home products that vaporize easily (adhesives, cleaners, plastics).
  • Formaldehyde is a common adhesive.
• Radon Gas: Radioactive gas from uranium decay; enters homes through cracks.

Natural Indoor Air Pollutants Affecting Respiratory Issues

• Dust settles naturally, irritating the respiratory tract when disturbed.
• Mold develops in dark, damp, unventilated areas.
• Lead paint in old homes is hazardous when ingested or inhaled.

Methods to Reduce Air Pollutants

• Regulatory practices, conservation practices, and alternative fuels.
• Vapor recovery nozzles prevent gas fumes from escaping.
• Catalytic converters turn pollutants into less harmful molecules.
• Wet and dry scrubbers remove particulates and gases from industrial exhaust.
• Scrubbers and electrostatic precipitators reduce pollution from coal-burning power plants.

Laws/Regulations

• Clean Air Act (CAA): Allows the EPA to set acceptable levels.
  • Monitors emissions levels and punishes corporations exceeding limits.;
• Pollution Credits: Companies with reduce emissions can sell them to others.
• CAFÉ Vehicle Standards: Requires vehicle manufacturers to work more to make more efficient vehicles

Vapor Reducing Nozzles

• Gases are captured and returned to an underground storage tank during refueling.
• Reduce both VOCs and the release of benzene from gas vapors.

Catalytic Converters

• Metals convert NOx, CO, and hydrocarbons into CO2, N2, O2, and H2O.

SOx and NOx Reduction Methods

• Crushed limestone is mixed with coal before burning to produce calcium sulfate.
• Fluidized bed combustion uses jets of air for more efficient combustion at lower temperatures.

Wet and Dry Scrubbers

• Dry Scrubbers: Use chemicals (like calcium oxide) to neutralize gases.
• Wet Scrubbers: Use chemical agents and mist nozzles to trap PM.

Electrostatic Precipitators

• Negatively charged electrodes collecting in charged plates trapping pollutants.

Acid Rain and Deposition

• Primarily caused by nitrogen oxides and sulfur oxides from anthropogenic sources.
• Originates mainly from coal-burning power plants and motor vehicles
• Occurs downwind communities from burning power plants.
• Acidifies soils and water bodies in addition to corroding human-made structures.

Sources of Nox and So2

• Main polluters are so2 coal fired power plants, metal factories, vehicles and Nox from diesel generators.
• Since the passing of clean air act, reduced acid deposition.
• Sulfuric and nitric acid dissociate in the presence of water into sulfate and nitrate ions and hydrogen ions

Soil/Water Acidification

• H+ ions displace nutrients from soil and make toxic metals more soluble.
• Aquatic species have different PH preferences but at certain levels, they cannot survive.
• Limestone is use to neutralized soil/water

Pollution

• Sounds lead to physiological distress in the forms of construction traffic in urban areas.
• Animals go into stress that can damaged hearing and altered migration patterns.

Explore the causes, effects, and sources of common air pollutants such as nitrogen oxides, carbon monoxide, and lead. Understand their impact on health and the environment, and ways to mitigate these pollutants.