Air Pollution Notes

Air Pollution

Natural Sources of Air Pollution

• Air pollution can originate from natural sources.
• Natural sources are generally small contributors to overall air pollution levels.
• They can have a significant short-term impact, usually localized.
• Examples of particulate matter from natural sources:
  • Dust storms
  • Sandstorms
• Natural sources of $CO_2$:
  • Cellular respiration
  • Decomposition of organic matter
  • Wildfires
  • Volcanic eruptions

Human Activity as the Main Cause

• Human activity is the primary cause of air pollution.
• Air pollution tends to concentrate in areas with high population density due to transportation and industrial processes.

Primary and Secondary Air Pollutants

• Primary air pollutants: Directly emitted from the source.
• Secondary air pollutants: Formed as a result of primary pollutants reacting in the atmosphere.

Sources of Pollution: Point vs. Non-Point

Point Source Pollution

• Pollution from a single, identifiable source (e.g., a factory smokestack).
• Characteristics:
  • Discharge is easy to identify.
  • Fairly easy to monitor.
  • Relatively easy to control since the contaminant and location are known.
  • Industries can be fined for non-compliance.

Non-Point Source Pollution

• Pollution from multiple or diffused sources over a large area (e.g., car tailpipe exhaust).
• Characteristics:
  • Many small diffuse sources from different locations.
  • Difficult to monitor.
  • Individual contributions are smaller, but cumulative effects are significant.
  • Difficult to locate and fine offenders.

Different Air Pollutants

• Examples of air pollutants:
  • Carbon monoxide (CO)
  • Carbon dioxide ($CO_2$)
  • Nitric oxide (NO)
  • Nitrogen dioxide ($NO_2$)
  • Sulfur dioxide ($SO_2$)

Chemical Reactions Forming Air Pollutants

• Carbon monoxide (CO):
  • $2C + O_2 \rightarrow 2CO$
  • $C + O<em>2 \rightarrow CO</em>2$
• Nitric oxide (NO):
  • $N<em>2 + O</em>2 \rightarrow 2NO$
• Nitrogen dioxide ($NO_2$):
  • $2NO + O<em>2 \rightarrow 2NO</em>2$
• Sulfur dioxide ($SO_2$):
  • $S + O<em>2 \rightarrow SO</em>2$

Transportation and Industrial Processes

Transportation (Burning of Fossil Fuels)

• Releases nitrogen oxides:
  • Production of ozone.
  • Formation of photochemical smog.
  • Converts to nitric acid, causing acid rain.
• Other pollutants:
  • Carbon monoxide.
  • Hydrocarbons.
  • Particulate matter.
  • Sulfur dioxide (diesel fuels).

Industrial Processes (Burning of Coal and Fossil Fuels)

• Coal combustion releases:
  • Carbon dioxide.
  • Sulfur dioxide.
  • Toxic metals.
  • Particulates (soot).

Primary Pollution Types and Sources

• Primary Pollution Types:
  • Carbon monoxide - 49%
  • Sulfur dioxide - 16%
  • Nitrogen oxides - 15%
  • Volatile organic compounds (VOC) - 14%
  • Particulates - 6%
• Primary Pollution Sources:
  • Transportation - 46%
  • Stationary Sources Fuel Combustion - 27%
  • Industrial Processes - 15%
  • Miscellaneous - 9%

Measuring Air Pollutants

• Measured in parts per million (ppm).
• 1 ppm: one particle of pollutant per 999,999 particles of air.

U.S. Clean Air Act and National Ambient Air Quality Standards (EPA)

Carbon Monoxide (CO)

• Colorless, odorless, tasteless gas, slightly less dense than air.
• Forms when there is not enough oxygen to produce carbon dioxide.
  • Burning fossil fuels.
  • Volcanic eruption.
  • Fires.
• Toxic to animals.

Sulfur Dioxide ($SO_2$)

• Colorless gas with a penetrating, choking odor.
• Readily dissolves in water to form acid.
• Emitted from:
  • Burning fossil fuels.
    • Industrial plants.
    • Motor vehicles.
    • Oil refineries.
  • Tar-sand extraction.
  • Ore processing.
  • Volcanoes.
  • Marshes.
  • Hot Springs.
  • Forest fires.
• Toxic to plants (reduces crop yields).
• Irritating to the throat and lungs, damages the respiratory system.

Nitrogen Oxides (NO & $NO_2$)

• Produced when oxygen and nitrogen react in the air, usually in high-temperature combustion.
• Distinction from nitrous oxide ($N_2O$).

Particulate Matter

• Microscopic solid or liquid matter suspended in Earth’s atmosphere.
  • Size varies, average is 10 microns (human hair is 50 microns).
• Naturally Occurring:
  • Dust storms, wildfires, volcanoes.
• Man-Made:
  • Burning fossil fuels, burning waste, soil erosion, vehicle exhaust.
• Smaller and lighter particles stay in the air longer.

Lead (Pb)

• Toxic metal used in construction, lead-acid batteries, bullets, fishing weights, radiation shields.
• U.S. phased out tetraethyl lead (gasoline additive) in 1975.
• Human exposure:
  • Lead paint chips (U.S. banned lead paint in 1977).
  • Mining.
  • Burning waste/garbage.
  • Ingestion of lead-poisoned food or water.
• Symptoms of lead poisoning:
  • Difficulty for blood to produce hemoglobin.
  • Mental disabilities.
  • Hypertension (high blood pressure).
  • Miscarriages.

Ground Level Ozone

Ozone

• Ozone is $O_3$ and can be formed in different chemical reactions depending on its location in the atmosphere.

Good Ozone

• Stratospheric ozone layer.
• $3O<em>2 + uv \rightleftharpoons 2O</em>3$
• Filters out UV radiation, acts as a global sunscreen.

Bad Ozone

• Ground level (tropospheric) ozone is a secondary air pollutant.
• Causes:
  • Asthma & bronchitis.
  • Harm lung function & irritate the respiratory system.
  • Heart attacks.
  • Suppressed immune system.
• Produced through burning of fossil fuels.
  • $NO_2 + uv \rightarrow NO + O$
  • $O + O<em>2 \rightarrow O</em>3$
  • $NO<em>x + VOCs \rightarrow PANs + O</em>3$

Other Air Pollutants

PANs (Peroxyacyl Nitrates)

• Secondary pollutants causing:
  • Eye irritation.
  • Impaired immune system.
  • Respiratory problems.
  • Inhibited photosynthesis in plants.

VOCs (Volatile Organic Compounds)

• Organic chemicals that evaporate at room temperature.
• Naturally formed or man-made (burning of fossil fuels).
• Long-lasting health effects:
  • Cancer.
  • Brain, Liver, and Kidney damage.
  • Eye, nose, and throat irritation.
  • Headaches, dizziness, nausea.

Photochemical Smog (Smoke & Fog reacting in sunlight)

• Formed when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight.
• Vehicle emissions (exhaust fumes) are the largest contributor.
• Tends to form in the morning in large cities during commutes.
• Nitrogen oxides react with VOCs (hydrocarbons).
• VOCs (formaldehyde, gasoline) evaporate or sublimate at room temperature; trees are a natural source.
• Nitrogen oxides react with sunlight to produce ozone.
• Ozone peaks in the afternoon and is higher in the summer due to sunlight.

Motor Vehicle Air Pollution

Prevention

• Walk, bike, or use mass transit.

Reduction

• Require emission control devices.
• Improve fuel efficiency.
• Inspect car exhaust systems twice a year.
• Get older, polluting cars off the road.
• Set strict emission standards.

Industrial Smog

• Smog produced from industrial processes through burning of fossil fuels.
• Consists of sulfur dioxide ($SO_2$), suspended droplets of sulfuric acid, and suspended solid particles.

Thermal Inversion

• In the troposphere, atmospheric temperature decreases with increasing altitude.
• During a thermal inversion, a layer of warm air sits on top of a layer of cooler air.
• During the day, the sun heats the Earth’s surface, heat releases slowly and warm air rises.
• The warm air cools and becomes dense, and falls back towards the ground (convection).
• At night, the ground cools without sunlight. The ground takes heat from the air close to it, cooling the air closest to the ground.
• The ground layer of air is now cooler than the layer of air above it, forming a thermal inversion.
• When a thermal inversion forms over a city, smoke and other air pollutants can become trapped under it.
• Air pollution cannot rise to higher elevations and disperse, so it becomes more concentrated.
• Thermal inversion traps pollution close to the ground, especially smog and particulates.

Acid Rain (Deposition)

• Occurs when nitrogen oxides ($NO<em>x$) and sulfur oxides ($SO</em>x$) from man-made or natural sources react with water in the atmosphere.
• Nitric oxides come from motor vehicles and coal-burning power plants.
• Sulfur dioxides come from coal-burning power plants.
• Can fall as rain, snow, or sleet (wet deposition) or as dry, sulfur-containing particles.
• Mainly affects communities downwind from coal-burning power plants.
• Acidifies soils and bodies of water and corrodes human-made structures.
• Regional differences in soils and bedrock affect the impact.
• Acid inhibits plant growth and damages tissue in living organisms.

Prevention

• Reduce coal use and burn only low-sulfur coal.
• Use natural gas and renewable energy resources in place of coal.
• Remove $SO<em>2$ and $NO</em>x$ from smokestack gases and remove $NO_x$ from motor vehicular exhaust.
• Tax $SO_2$ emissions.

Cleanup

• Add lime to neutralize acidified lakes.
• Add phosphate fertilizer to neutralize acidified lakes.
• Add lime to neutralize acidified soils.

Reduction of Air Pollutants

• Methods: regulatory practices, conservation practices, and alternative fuels.
  • Ban open burning of waste.
  • Buy smaller cars & energy efficient appliances.
  • Decrease unnecessary travel.
  • Distribute solar cook stoves to developing countries.
  • Reduce idling and turn off engines while waiting.
  • Use mass transit or carpool when possible.
  • Toughen legislation to reduce sulfur content in fuel.

Catalytic Converter

• Air pollution control device for internal combustion engines.
• Converts pollutants (CO, $NO<em>x$, and hydrocarbons) in exhaust into less harmful molecules ($CO</em>2$, $N<em>2$, $O</em>2$, and $H_2O$).
• Does not reduce the amount of $CO_2$ emissions.
• EPA states catalytic converters are a significant and growing cause of global warming because of their release of nitrous oxide ($N_2O$) - a greenhouse gas.

Vapor Recovery Nozzle

• Air pollution control device on a gasoline pump that prevents fumes from escaping into the atmosphere when fueling a motor vehicle.

Reducing Air Pollution from Coal Burning Power Plants

Electrostatic Precipitator

• Filtration device using static electricity to remove particles (dust and smoke) from exhaust gas before release.
• 99% efficiency rate.

Wet and Dry Scrubbers

• Air pollution control devices that remove particulates and/or gases from industrial exhaust streams.

Wet Scrubbers

• Saturate the waste stream with moisture to remove particles.
• Water is sprayed on gas streams to remove dust and particulate matter.

Dry Scrubbers

• Use dry reactant to clean the gas stream.
• Spray dry absorbent reagents to remove pollutants.

Indoor Air Pollutants

• Pollutants accumulate inside homes, schools, workshops, and vehicles.
• Concentrations can be higher indoors than outside.
• Carbon monoxide is an asphyxiant.
• Particulates include asbestos, dust, and smoke.
  • Asbestos was phased out in the mid 1970s due to causing lung cancer.
• Indoor air pollution can cause “sick building” syndrome (SBS).
  • A combination of ailments associated with an individual’s place of work or residence.

Sources of Indoor Air Pollutants

• Natural sources, human-made sources, and combustion.

Common Natural Source Indoor Air Pollutants

• Radon, mold, and dust.

Radon-222

• Naturally occurring radioactive gas produced by the decay of uranium in rocks and soils.
• Infiltrates homes through soil, basements, or cracks in walls/foundation, and dissolved in groundwater.
• Exposure can lead to radon-induced lung cancer, the second leading cause of lung cancer in America.

Common Human-Made Indoor Air Pollutants

• Insulation, VOCs from furniture, paneling and carpets; formaldehyde from building materials, furniture, upholstery, and carpeting; and lead from paints (prior to 1978).

Common Combustion Air Pollutants

• Carbon monoxide, nitrogen oxides, sulfur dioxide, particulates, and tobacco smoke.

Indoor Air Pollution Solutions

Prevention

• Ban indoor smoking.
• Set stricter formaldehyde emissions standards for carpet, furniture, and building materials.
• Prevent radon infiltration.
• Use naturally based cleaning agents, paints, and other products.

Reduction and Dilution

• Use adjustable fresh air vents for work spaces.
• Circulate air more frequently.
• Circulate a building's air through rooftop greenhouses.
• Use solar cookers and efficient, vented wood-burning stoves.