♻️AP Environmental Science Unit 7 – Atmospheric Pollution

Key Concepts and Definitions

• Atmospheric pollution refers to the presence of substances in the atmosphere that can harm human health, the environment, and climate
• Primary pollutants are emitted directly from sources (carbon monoxide, sulfur dioxide, nitrogen oxides)
• Secondary pollutants form in the atmosphere through chemical reactions (ozone, sulfuric acid, nitric acid)
• Criteria air pollutants are common air pollutants regulated by the EPA (particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, lead)
• Hazardous air pollutants, also known as toxic air pollutants, can cause serious health effects (benzene, mercury, asbestos)
• Particulate matter (PM) consists of solid particles and liquid droplets suspended in the air
  • PM10 refers to particles with diameters less than 10 micrometers
  • PM2.5 refers to fine particles with diameters less than 2.5 micrometers
• Smog is a type of air pollution that reduces visibility and can cause respiratory issues
  • Photochemical smog forms when nitrogen oxides and volatile organic compounds react in the presence of sunlight
  • Industrial smog, also known as sulfurous smog, is caused by the burning of coal and contains high levels of sulfur oxides

Sources of Atmospheric Pollution

• Stationary sources include power plants, factories, and industrial facilities that emit pollutants from a fixed location
• Mobile sources include vehicles (cars, trucks, buses) and other transportation modes (airplanes, ships) that emit pollutants while moving
• Fossil fuel combustion from power generation, transportation, and industrial processes releases carbon dioxide, sulfur dioxide, and nitrogen oxides
• Agricultural activities contribute to air pollution through livestock emissions (methane), fertilizer use (ammonia), and crop burning
• Natural sources of air pollution include volcanic eruptions, wildfires, and dust storms
• Indoor air pollution sources include cooking and heating with solid fuels (wood, coal), tobacco smoke, and volatile organic compounds from cleaning products and building materials
• Fugitive emissions are unintended leaks or releases from industrial processes or equipment (pipelines, storage tanks, valves)

Types of Air Pollutants

• Sulfur dioxide (SO2) is a colorless gas with a pungent odor, primarily produced by fossil fuel combustion at power plants and industrial facilities
• Nitrogen oxides (NOx) include nitric oxide (NO) and nitrogen dioxide (NO2), formed during high-temperature combustion processes (vehicle engines, power plants)
• Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion of fossil fuels (vehicle exhaust, industrial processes)
• Volatile organic compounds (VOCs) are organic chemicals that easily evaporate at room temperature (benzene, formaldehyde, methylene chloride)
  • VOCs contribute to the formation of ground-level ozone and smog
• Ozone (O3) is a secondary pollutant formed when NOx and VOCs react in the presence of sunlight
  • Ground-level ozone is a major component of photochemical smog and can harm respiratory health
• Particulate matter (PM) can be directly emitted (primary particles) or formed in the atmosphere (secondary particles)
  • Primary particles include dust, soot, and sea salt
  • Secondary particles form through chemical reactions (sulfates, nitrates, organic compounds)
• Lead (Pb) is a toxic metal that can be emitted from industrial processes, lead-based paint, and leaded gasoline (phased out in most countries)

Health and Environmental Impacts

• Short-term exposure to air pollution can cause respiratory irritation, coughing, wheezing, and aggravate asthma symptoms
• Long-term exposure to air pollution increases the risk of respiratory diseases (chronic obstructive pulmonary disease, lung cancer), cardiovascular diseases, and premature death
• Particulate matter can penetrate deep into the lungs and enter the bloodstream, causing inflammation and oxidative stress
• Ozone exposure can reduce lung function, aggravate asthma, and increase susceptibility to respiratory infections
• Air pollution contributes to acid rain formation when sulfur dioxide and nitrogen oxides react with water and oxygen in the atmosphere
  • Acid rain can acidify soils and water bodies, harming aquatic life and vegetation
• Atmospheric pollution can reduce visibility and cause haze, impacting air quality and aesthetics
• Air pollutants can damage crops and vegetation by reducing photosynthesis, stunting growth, and increasing susceptibility to pests and diseases
• Deposition of air pollutants (mercury, persistent organic pollutants) can contaminate soil and water, entering the food chain and bioaccumulating in organisms

Measurement and Monitoring Techniques

• Ambient air quality monitoring networks measure pollutant concentrations in the outdoor air using strategically placed monitoring stations
• Continuous emission monitoring systems (CEMS) measure pollutant emissions directly from the source (power plant stacks, industrial facilities)
• Passive sampling techniques use devices that collect pollutants over time without requiring a power source (diffusion tubes, passive badges)
• Active sampling techniques use pumps to draw air through a collection medium (filters, sorbent tubes) for analysis
• Remote sensing techniques use satellite imagery and ground-based instruments to measure pollutant concentrations over large areas
  • Differential Optical Absorption Spectroscopy (DOAS) measures atmospheric trace gases by analyzing light absorption spectra
• Biomonitoring uses living organisms (lichens, mosses) as indicators of air pollution levels and environmental health
• Air quality index (AQI) communicates the level of air pollution and associated health risks to the public using a color-coded scale

Pollution Control Strategies

• Source control strategies aim to reduce or eliminate pollutant emissions at the source
  • Fuel switching involves transitioning from high-polluting fuels (coal) to cleaner alternatives (natural gas, renewable energy)
  • Process modifications optimize industrial processes to minimize pollutant formation and improve efficiency
• Emission control technologies capture or destroy pollutants before they are released into the atmosphere
  • Scrubbers remove pollutants (sulfur dioxide, particulate matter) from exhaust gases using a liquid or solid sorbent
  • Electrostatic precipitators use an electric field to remove particulate matter from exhaust gases
  • Catalytic converters reduce nitrogen oxide, carbon monoxide, and hydrocarbon emissions from vehicle exhaust
• Urban planning strategies reduce air pollution by promoting sustainable transportation (public transit, cycling, walking) and green spaces
• Energy efficiency measures (building insulation, efficient appliances) reduce energy consumption and associated pollutant emissions
• Renewable energy sources (solar, wind, hydro) generate electricity with minimal air pollutant emissions compared to fossil fuels

Regulations and Policies

• The Clean Air Act (CAA) is the primary federal law regulating air quality in the United States
  • National Ambient Air Quality Standards (NAAQS) set maximum allowable concentrations for criteria air pollutants
  • New Source Performance Standards (NSPS) regulate emissions from new or modified stationary sources
• The Environmental Protection Agency (EPA) is responsible for implementing and enforcing the Clean Air Act
• State Implementation Plans (SIPs) outline how each state will attain and maintain NAAQS
• Emission trading programs (cap-and-trade) set a limit on total emissions and allow sources to trade emission allowances
• Vehicle emission standards regulate tailpipe emissions from new vehicles (passenger cars, trucks, buses)
• International agreements, such as the Montreal Protocol and the Paris Agreement, address global air pollution and climate change issues
• Environmental justice initiatives aim to reduce the disproportionate impact of air pollution on disadvantaged communities

Case Studies and Current Issues

• The London Smog of 1952 was a severe air pollution event that caused thousands of premature deaths and led to the passage of the Clean Air Act in the UK
• The Beijing Air Pollution Crisis highlights the challenges of rapid urbanization and industrialization in developing countries
  • China has implemented a series of measures to reduce air pollution, including emission standards, coal-use restrictions, and renewable energy targets
• The Volkswagen Emissions Scandal revealed the use of defeat devices to circumvent vehicle emission standards, undermining air quality regulations
• The use of wood-burning stoves and fireplaces contributes to particulate matter pollution in many urban areas, leading to restrictions and educational campaigns
• The COVID-19 pandemic led to temporary reductions in air pollution due to lockdowns and reduced economic activity, providing insights into the potential for air quality improvements
• Environmental justice concerns have highlighted the need for equitable air pollution reduction strategies that prioritize the health of vulnerable communities
• Climate change and air pollution are closely linked, as many air pollutants (carbon dioxide, black carbon) also contribute to global warming
  • Addressing air pollution can provide co-benefits for climate change mitigation and public health