7.1 Introduction to Air Pollution (Pollutants)

Air Pollution Basics

  • Coal Combustion:

    • Sources include electricity generation. Impacts created: respiratory irritation, smog, and acid precipitation.

  • Fossil Fuel/Biomass Combustion:

    • Similar impact patterns, affecting respiratory systems and contributing to smog formation.

Types of Air Pollutants

  • Pollutants:

    • SO2: Sulfur dioxide

    • NOx: Nitrogen oxides (NO & NO2)

    • CO: Carbon monoxide

    • PM: Particulate matter

    • Ozone (tropospheric)

    • Lead (Pb)

Criteria Air Pollutants

  • Following the Clean Air Act (1970), the EPA is required to set acceptable limits for six criteria air pollutants and enforce monitoring.

Air Pollutants vs. Greenhouse Gasses

  • Carbon Dioxide (CO2):

    • CO2 is NOT one of the six criteria pollutants identified in the Clean Air Act.

    • Supreme Court Ruling in 2007: Found that the EPA could regulate greenhouse gases, leading to regulations starting in 2009.

    • Not classified as a direct air quality lowering agent concerning human health; not toxic to organisms; does not cause lung/eye damage or lead to smog.

    • Recognized as a greenhouse gas; contributes to earth warming leading to environmental and human health consequences.

    • In APES (Advanced Placement Environmental Science), CO2 is typically excluded from frequent reference questions involving air pollutants (focus instead on SO2, NOx, O3, PM).

Coal Combustion

  • Impact & Emissions:

    • Coal combustion releases more air pollutants compared to other fossil fuels.

    • Accounts for approximately 35% of global electricity.

    • Releases include:

    • CO (Carbon monoxide)

    • CO2 (Carbon dioxide)

    • SO2 (Sulfur dioxide)

    • NOx (Nitrogen oxides)

    • Toxic metals (mercury, arsenic, lead)

    • Particulate matter (often carries toxic metals).

Effects of SO2

  • Health Impacts:

    • Acts as a respiratory irritant (causing inflammation of bronchioles and lungs), and worsens conditions such as asthma and bronchitis.

  • Environmental Effects:

    • Sulfur aerosols (suspended sulfate particles) block incoming sunlight, reducing visibility and photosynthesis.

    • Forms sulfurous (grey) smog.

    • Combines with water and O2 in the atmosphere to form sulfuric acid, resulting in acid precipitation.

Nitrogen Oxides (NOx)

  • Sources:

    • Released by the combustion of any source, especially fossil fuels and biomass.

  • Definition:

    • NOx refers to nitrogen oxides, particularly NO (nitric oxide) and NO2 (nitrogen dioxide).

  • Formation:

    • NO is formed when nitrogen (N2) combines with oxygen (O2), notably during combustion processes.

  • Transformation:

    • NO can become NO2 by reacting with ozone (O3) or O2.

    • Sunlight plays a role in converting NO2 back into NO.

Environmental and Human Health Impacts of NOx

  • Health Impacts:

    • Acts as a respiratory irritant.

    • Leads to the formation of tropospheric ozone (O3), contributing to photochemical smog.

    • Combines with water and O2 in the atmosphere to form nitric acid, leading to acid precipitation.

EPA & Lead

  • Historical Context:

    • Before the Clean Air Act, lead was widely used as a gasoline additive.

    • EPA initiated the phaseout of lead from gasoline in 1974.

  • Catalytic Converters:

    • Vehicles manufactured after 1974 are mandated to have catalytic converters to reduce emissions of NOx, CO, and hydrocarbons.

    • Lead is known to damage catalytic converters and is recognized as a neurotoxin affecting human nervous systems.

Primary vs. Secondary Air Pollutants

  • Primary Pollutants:

    • Emitted directly from sources such as vehicles, power plants, factories, and natural sources (e.g., volcanoes, forest fires).

  • Secondary Pollutants:

    • Formed through transformations in the presence of sunlight, water, O2. Examples include:

    • Tropospheric ozone (O3)

    • Sulfuric acid (H2SO4) & sulfate (SO_4^{2-})

    • Nitric acid (HNO3) & nitrate (NO3^{-}).

7.2 Photochemical Smog

Reducing Photochemical Smog

  • Methods:

    • Reduction in emissions of nitrogen oxides and VOCs is essential in decreasing photochemical smog formation.

  • Health Effects:

    • Photochemical smog poses several human health risks, including respiratory issues and eye irritation.

Components of Photochemical Smog Formation

  • Precursor Pollutants:

    • Major contributors include nitrogen oxides (NO2) and VOCs.

  • Process:

    • NO2 breaks down under sunlight into NO and free oxygen atoms which then bond with O2 to form ozone (O3).

    • VOCs are carbon-based compounds that vaporize easily, binding with NO to generate photochemical oxidants.

Conditions Favoring Smog Formation

  • Warmth:

    • Higher atmospheric temperatures accelerate ozone formation and the evaporation of VOCs, thereby enhancing smog formation.

  • Sources of VOCs and NO:

    • Common sources include gas stations, laundromats, and petrochemical factories.

  • Urban Areas:

    • Experience elevated smog levels due to a combination of higher vehicle traffic leading to increased NO2 emissions, higher temperatures from blacktop surfaces, and greater VOC emissions from gas stations and factories.

Normal Ozone Formation Cycle

  • Morning Commute Scenario:

    • High NO2 emissions from vehicle exhaust during morning hours.

    • Sunlight initiates breakdown of NO2 to produce NO and O.

    • O atoms bond with O2, forming O3.

  • Nighttime Reaction:

    • Ozone reacts with NO leading to a conversion back to NO2 and O2, resulting in reduced O3 levels overnight.

Photochemical Smog Dynamics

  • Formation:

    • Increased concentrations of NO2 during the day under sunlight lead to an accumulation of ozone rather than returning to NO2 and O2 at night, causing photochemical smog buildup.

Factors Contributing to Increased Smog Formation

  • Increased VOC emissions due to proximity to sources.

  • Higher vehicle traffic correlates directly with NO2 emissions, thus affecting ozone formation.

  • More sunlight and warmer temperatures facilitate increased reactions leading to smog development.

  • Urban complications include:

    • More traffic leading to higher NO2 levels

    • Greater heat retention due to low albedo of surfaces

    • Increased VOC emissions from various industries and nearby power plants.

Environmental Impacts of Photochemical Smog

  • Effects on Environment:

    • Reduces sunlight, which limits photosynthesis.

  • Economic Costs:

    • Advancements towards reducing vehicle emissions can lead to accumulated savings over time.

  • Impacts on Human Health:

    • Respiratory irritations resulting from increased O3 impact individuals with asthma, bronchitis, and other respiratory conditions.

    • Economic impact through increased healthcare costs related to illnesses associated with smog.

7.3 Thermal Inversion

Urban Heat Island Effect

  • Urban areas often exhibit higher surface and air temperatures compared to surrounding suburbs and rural areas.

  • Contributing Factors:

    • Lower albedo of materials like concrete and asphalt, which absorb more solar energy.

    • Reduced evapotranspiration affecting local cooling mechanisms, allowing urban areas to retain more heat than greener surrounding areas.

Normal Temperature Gradient vs. Thermal Inversion

  • Typical Scenario:

    • The atmosphere cools with altitude in usual conditions enabling convection to carry air pollutants away.

  • Thermal Inversion:

    • Cooler air is trapped beneath warmer air above, inhibiting the upward movement of pollutants. This occurs either due to:

    • A warm front moving over a cooler area.

    • Hot surfaces cooling at night while the heat from the day is still radiating.

Effects of Thermal Inversion

  • Pollution Accumulation:

    • Traps smog, particulate matter, ozone, sulfur dioxide (SO2), and nitrogen oxides (NOx) close to the Earth's surface.

  • Health Impacts:

    • Increased respiratory irritation, exacerbation of asthma, and possible hospitalization due to worsened chronic obstructive pulmonary disease (COPD).

    • Detrimental effects on tourism and decreased photosynthesis rates due to poor air quality.

7.1 Introduction to Air Pollution (Pollutants)
Air Pollution Basics

  • Coal Combustion: Major source of electricity; leads to respiratory issues, smog, and acid rain.

  • Fossil Fuel/Biomass Combustion: Similar effects on respiratory health and smog formation.

Types of Air Pollutants

  • Pollutants: SO2, NOx, CO, PM, Ozone, Pb.

Criteria Air Pollutants

  • EPA sets limits on six criteria pollutants under the Clean Air Act.

Air Pollutants vs. Greenhouse Gasses

  • CO2: Not a criteria pollutant; regulated since 2009; known greenhouse gas contributing to global warming.

Coal Combustion

  • Emissions: Releases CO, CO2, SO2, NOx, toxic metals, and PM; accounts for 35% global electricity.

Effects of SO2

  • Health: Respiratory irritant, worsens asthma, bronchitis.

  • Environment: Reduces sunlight, visibility; leads to acid rain.

Nitrogen Oxides (NOx)

  • Sources: Produced from fossil fuel/biomass combustion.

  • Health Effects: Respiratory irritant; contributes to photochemical smog and acid rain.

EPA & Lead

  • History: Lead phased out from gasoline since 1974; contributes to catalytic converter damage.

Primary vs. Secondary Air Pollutants

  • Primary: Directly emitted (e.g., vehicle exhaust).

  • Secondary: Formed from reactions (e.g., ozone, sulfuric acid).

7.2 Photochemical Smog
Reducing Photochemical Smog

  • Focus on reducing nitrogen oxides and VOCs emissions.

Components of Photochemical Smog

  • Precursor Pollutants: Major contributors include NO2 and VOCs.

  • Formation Process: NO2 breaks down in sunlight, producing ozone.

Conditions Favoring Smog

  • Higher temperatures, vehicle traffic, and VOC emissions increase smog.

Ozone Formation Cycle

  • Daytime: NO2 from vehicles leads to ozone formation; Nighttime: Ozone converts back to NO2.

Factors Increasing Smog

  • More traffic, sunlight, and elevated temperatures facilitate smog development.

7.3 Thermal Inversion
Urban Heat Island Effect

  • Urban areas are warmer due to low albedo surfaces.

Normal Temperature Gradient vs. Thermal Inversion

  • Normal: Cool air rises; Inversion: Traps cool air beneath warmer layer.

Effects of Thermal Inversion

  • Traps pollutants, worsening air quality; health impacts include respiratory issues and economic costs.