🌿Intro to Environmental Science Unit 8 – Atmospheric Science & Air Pollution

Basics of Atmospheric Science

• Atmospheric science studies the Earth's atmosphere, its processes, and how it affects the environment and human activities
• Encompasses disciplines such as meteorology (weather forecasting), climatology (long-term climate patterns), and atmospheric chemistry (chemical composition and reactions in the atmosphere)
• Investigates the physical, chemical, and dynamical processes that occur in the atmosphere
• Utilizes various tools and techniques for data collection and analysis, including weather balloons, radar, satellites, and computer modeling
• Plays a crucial role in understanding and predicting weather events, climate change, and air pollution
• Helps develop strategies for mitigating the impacts of atmospheric phenomena on human health, ecosystems, and infrastructure
• Collaborates with other Earth science disciplines (hydrology, oceanography, and geology) to gain a comprehensive understanding of the Earth system

Composition and Structure of Earth's Atmosphere

• Earth's atmosphere is a thin layer of gases surrounding the planet, held in place by gravity
• Composed primarily of nitrogen (78%) and oxygen (21%), with the remaining 1% consisting of trace gases such as argon, carbon dioxide, and water vapor
• Divided into five main layers based on temperature changes: troposphere, stratosphere, mesosphere, thermosphere, and exosphere
  • Troposphere is the lowest layer, extending from the Earth's surface to an average height of 12 km, where most weather phenomena occur
  • Stratosphere extends from the top of the troposphere to about 50 km, containing the ozone layer that absorbs harmful ultraviolet radiation from the sun
• Atmospheric pressure decreases exponentially with altitude, with half of the atmosphere's mass contained within the lowest 5.6 km
• Atmospheric composition has changed over Earth's history due to natural processes (volcanic eruptions, biological activity) and human activities (fossil fuel combustion, land-use changes)
• Greenhouse gases (carbon dioxide, methane, water vapor) in the atmosphere trap heat and contribute to the greenhouse effect, which helps regulate Earth's temperature
• Atmospheric circulation patterns, driven by uneven heating of the Earth's surface and the Coriolis effect, redistribute heat and moisture across the planet

Weather Systems and Climate Patterns

• Weather refers to the short-term state of the atmosphere at a specific location and time, characterized by temperature, humidity, precipitation, wind, and other variables
• Climate describes the long-term average weather conditions and patterns in a given area, typically over a period of 30 years or more
• Weather systems develop due to interactions between air masses with different properties (temperature, humidity, and pressure)
  • High-pressure systems are associated with clear skies and stable weather, while low-pressure systems often bring cloudy and stormy conditions
• Global atmospheric circulation patterns, such as the Hadley, Ferrel, and Polar cells, influence the distribution of heat, moisture, and wind across the planet
• Jet streams, fast-moving air currents in the upper troposphere, play a significant role in steering weather systems and influencing global weather patterns
• Climate patterns, such as the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), can have far-reaching impacts on regional weather and climate
• Climate change, primarily driven by human activities that increase greenhouse gas concentrations in the atmosphere, is causing long-term shifts in temperature, precipitation patterns, and the frequency and intensity of extreme weather events

Types and Sources of Air Pollutants

• Air pollutants are substances in the atmosphere that can harm human health, the environment, and property
• Primary pollutants are emitted directly from sources, while secondary pollutants form through chemical reactions in the atmosphere
• Major air pollutants include particulate matter (PM), ground-level ozone (O₃), carbon monoxide (CO), sulfur dioxide (SO₂), nitrogen oxides (NOₓ), and volatile organic compounds (VOCs)
  • PM consists of tiny solid or liquid particles suspended in the air, classified by size (PM10, PM2.5) and can penetrate deep into the lungs
  • Ground-level ozone is a secondary pollutant formed by reactions between NOₓ and VOCs in the presence of sunlight, a major component of smog
• Sources of air pollutants can be natural or anthropogenic (human-caused)
  • Natural sources include volcanic eruptions, wildfires, and dust storms
  • Anthropogenic sources include fossil fuel combustion (power plants, vehicles), industrial processes, agriculture, and waste incineration
• Indoor air pollution, caused by sources such as cooking, heating, and building materials, can also pose significant health risks
• Long-range transport of air pollutants can affect areas far from the original emission sources, leading to regional and global air quality issues

Air Quality Measurements and Standards

• Air quality measurements are used to assess the levels of pollutants in the atmosphere and determine compliance with air quality standards
• Pollutant concentrations are typically measured in parts per million (ppm), parts per billion (ppb), or micrograms per cubic meter (μg/m³)
• Air quality monitoring networks, consisting of fixed stations and mobile sensors, continuously collect data on pollutant concentrations
• Air quality index (AQI) is a scale used to communicate the level of air pollution and associated health risks to the public
  • AQI values range from 0 to 500, with higher values indicating worse air quality and greater health concerns
  • AQI categories include: good (0-50), moderate (51-100), unhealthy for sensitive groups (101-150), unhealthy (151-200), very unhealthy (201-300), and hazardous (301-500)
• Air quality standards are legal limits on the maximum allowable concentrations of specific pollutants in the atmosphere
  • National Ambient Air Quality Standards (NAAQS) in the United States set limits for six criteria pollutants: PM, O₃, CO, SO₂, NO₂, and lead
  • Other countries and international organizations (World Health Organization) have their own air quality guidelines and standards
• Compliance with air quality standards is determined by comparing measured pollutant concentrations to the established limits over specified averaging times (hourly, daily, annual)

Health and Environmental Impacts of Air Pollution

• Air pollution can have severe consequences for human health, ecosystems, and the built environment
• Short-term exposure to high levels of air pollutants can cause respiratory irritation, aggravate asthma, and increase the risk of heart attacks and strokes
• Long-term exposure to air pollution is linked to chronic respiratory diseases (emphysema, bronchitis), cardiovascular diseases, and lung cancer
  • Particulate matter is particularly harmful, as small particles can penetrate deep into the lungs and enter the bloodstream
  • Ozone can damage lung tissue and reduce lung function, especially in children, the elderly, and those with pre-existing respiratory conditions
• Air pollution can have adverse effects on the environment, including:
  • Acid rain, caused by SO₂ and NOₓ emissions, which can damage forests, aquatic ecosystems, and buildings
  • Eutrophication of water bodies due to nitrogen deposition, leading to algal blooms and oxygen depletion
  • Reduced visibility and haze in urban and natural areas
• Climate change is exacerbated by air pollutants that also act as greenhouse gases (CO₂, methane) or contribute to the formation of ozone, a short-lived climate pollutant
• Vulnerable populations, such as children, the elderly, and those with pre-existing health conditions, are at higher risk of experiencing the negative impacts of air pollution

Air Pollution Control Technologies

• Air pollution control technologies are designed to reduce emissions from various sources and improve air quality
• Source control methods aim to prevent or minimize the release of pollutants at the point of generation
  • Examples include fuel switching (coal to natural gas), process modifications, and leak detection and repair programs
• Emission control devices are installed on pollution sources to capture or destroy pollutants before they are released into the atmosphere
  • Particulate matter control devices include cyclones, electrostatic precipitators (ESPs), and baghouses, which use physical processes (centrifugal force, electrostatic attraction, filtration) to remove particles from exhaust gases
  • Gaseous pollutant control devices include scrubbers (wet or dry), which use chemical reactions to remove pollutants such as SO₂ and acid gases, and selective catalytic reduction (SCR) systems, which use ammonia and a catalyst to convert NOₓ into nitrogen and water
• Mobile source control technologies focus on reducing emissions from vehicles and other mobile equipment
  • Catalytic converters, which use precious metal catalysts to convert pollutants (CO, NOₓ, VOCs) into less harmful compounds, are required on most modern vehicles
  • Diesel particulate filters (DPFs) capture PM emissions from diesel engines, while diesel oxidation catalysts (DOCs) reduce CO and VOC emissions
• Renewable energy technologies, such as wind and solar power, can help reduce air pollution by displacing fossil fuel-based electricity generation
• Energy efficiency measures, such as building insulation and high-efficiency appliances, can reduce energy demand and associated air pollutant emissions

Policy and Regulations for Air Quality Management

• Air quality policies and regulations are essential for protecting public health and the environment by setting standards, implementing control measures, and enforcing compliance
• The Clean Air Act (CAA) is the primary federal law in the United States governing air pollution control
  • The CAA requires the Environmental Protection Agency (EPA) to set NAAQS, regulate emissions from stationary and mobile sources, and implement programs to address regional air quality issues
  • State Implementation Plans (SIPs) outline how each state will attain and maintain compliance with the NAAQS
• The National Emissions Standards for Hazardous Air Pollutants (NESHAPs) regulate emissions of toxic air pollutants, such as mercury, benzene, and asbestos, from specific industrial sources
• The New Source Performance Standards (NSPS) set emission limits for new, modified, or reconstructed stationary sources in various industrial categories
• The Clean Air Act Amendments of 1990 introduced market-based approaches, such as the Acid Rain Program and the NOₓ Budget Trading Program, which use cap-and-trade mechanisms to reduce SO₂ and NOₓ emissions from power plants
• The Cross-State Air Pollution Rule (CSAPR) addresses the interstate transport of ozone and PM2.5 precursors (SO₂ and NOₓ) from power plants
• International agreements, such as the Montreal Protocol (ozone-depleting substances) and the Paris Agreement (greenhouse gas emissions), aim to address global air quality and climate change issues
• Local and regional air quality management agencies develop and implement plans to attain and maintain compliance with air quality standards, often through measures such as transportation planning, land-use zoning, and industrial permitting