🔆Environmental Chemistry I Unit 3 – Atmospheric Pollution and Greenhouse Gases

Key Atmospheric Pollutants

• Sulfur dioxide (SO2) contributes to acid rain formation and respiratory issues
• Nitrogen oxides (NOx) play a role in smog formation and acid rain
  • Nitrogen dioxide (NO2) is a reddish-brown toxic gas
  • Nitric oxide (NO) is a colorless gas that oxidizes to form NO2
• Particulate matter (PM) consists of solid and liquid particles suspended in the air
  • PM10 refers to particles with a diameter of 10 micrometers or less
  • PM2.5 refers to fine particles with a diameter of 2.5 micrometers or less
• Carbon monoxide (CO) is a colorless, odorless, and toxic gas that reduces oxygen delivery to the body's organs
• Volatile organic compounds (VOCs) are organic chemicals that easily evaporate at room temperature (benzene, formaldehyde)
• Ozone (O3) is a secondary pollutant formed by the reaction of NOx and VOCs in the presence of sunlight
  • Ground-level ozone is a major component of smog and can cause respiratory issues
• Lead (Pb) is a toxic heavy metal that can accumulate in the body and cause neurological damage

Sources of Atmospheric Pollution

• Stationary sources include power plants, industrial facilities, and residential heating
  • Coal-fired power plants are a significant source of SO2 and NOx emissions
  • Industrial processes such as metal smelting and chemical manufacturing release various pollutants
• Mobile sources include vehicles, ships, and aircraft
  • Gasoline-powered vehicles emit CO, NOx, and VOCs
  • Diesel engines are a major source of PM emissions
• Natural sources contribute to atmospheric pollution
  • Volcanic eruptions release SO2 and ash particles
  • Wildfires emit PM, CO, and VOCs
• Agricultural activities release ammonia (NH3) from fertilizers and livestock waste
• Fugitive emissions occur from leaks, evaporation, or unintended releases (gas leaks, solvent evaporation)
• Indoor sources of air pollution include cooking, heating, and consumer products (cleaning agents, paints)

Greenhouse Gases and Their Properties

• Carbon dioxide (CO2) is the most significant anthropogenic greenhouse gas
  • Atmospheric CO2 concentrations have increased from pre-industrial levels of ~280 ppm to over 400 ppm
  • CO2 has a long atmospheric lifetime and contributes to long-term climate change
• Methane (CH4) is a potent greenhouse gas with a global warming potential 28-36 times that of CO2 over a 100-year period
  • Major sources include agriculture, landfills, and natural gas production
• Nitrous oxide (N2O) has a global warming potential 265-298 times that of CO2 over a 100-year period
  • Agricultural soil management and industrial processes are major sources
• Water vapor (H2O) is the most abundant greenhouse gas, but its atmospheric concentration is not directly affected by human activities
• Ozone (O3) in the troposphere acts as a greenhouse gas
• Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are potent greenhouse gases that also deplete the ozone layer
  • The Montreal Protocol has successfully phased out the production of these substances

Atmospheric Chemistry Basics

• Photochemical reactions are driven by sunlight and play a crucial role in atmospheric chemistry
  • Photolysis of NO2 leads to the formation of ozone in the troposphere
  • Photolysis of ozone in the stratosphere creates the ozone layer that protects Earth from harmful UV radiation
• Oxidation reactions involve the transfer of electrons from one molecule to another
  • Hydroxyl radicals (OH) are the primary oxidizing agent in the atmosphere and help remove pollutants
• Acid-base reactions in the atmosphere contribute to the formation of acid rain
  • SO2 and NOx react with water to form sulfuric acid (H2SO4) and nitric acid (HNO3)
• Adsorption and deposition processes remove pollutants from the atmosphere
  • Dry deposition involves the direct settling of particles or gases onto surfaces
  • Wet deposition occurs when pollutants are removed by precipitation (rain, snow)
• Atmospheric lifetime refers to the average time a molecule spends in the atmosphere before being removed by chemical reactions or deposition
• Dispersion and transport of pollutants are influenced by atmospheric stability, wind patterns, and topography

Environmental Impacts of Air Pollution

• Acid rain occurs when SO2 and NOx react with water in the atmosphere to form acidic compounds
  • Acid rain can acidify soils and water bodies, harming aquatic life and vegetation
  • It can also corrode buildings and infrastructure
• Eutrophication is the excessive growth of algae in water bodies due to nutrient enrichment from nitrogen deposition
  • Algal blooms can deplete oxygen levels, creating "dead zones" and harming aquatic ecosystems
• Smog is a mixture of air pollutants, including ozone, PM, and NOx, that reduces visibility and air quality
  • Photochemical smog is formed by the reaction of NOx and VOCs in the presence of sunlight
• Respiratory health effects include aggravation of asthma, chronic bronchitis, and decreased lung function
  • Particulate matter can penetrate deep into the lungs and cause inflammation
• Cardiovascular health effects include increased risk of heart attacks and strokes
• Ecosystem damage can occur due to the deposition of acidic and nitrogen-containing compounds
  • Acid rain can leach nutrients from soils and damage plant foliage
  • Nitrogen deposition can lead to biodiversity loss in sensitive ecosystems

Climate Change and Global Warming

• The greenhouse effect is the process by which greenhouse gases trap heat in the atmosphere
  • Greenhouse gases absorb and re-emit infrared radiation, warming the Earth's surface
• Radiative forcing measures the difference between incoming and outgoing energy in the Earth's atmosphere
  • Positive radiative forcing leads to warming, while negative radiative forcing leads to cooling
• Global temperature rise is a consequence of increased greenhouse gas concentrations
  • The Earth's average surface temperature has increased by approximately 1°C since pre-industrial times
• Sea level rise occurs due to thermal expansion of ocean water and melting of land-based ice (glaciers, ice sheets)
  • Projected sea level rise by 2100 ranges from 0.3 to 1.1 meters, depending on greenhouse gas emission scenarios
• Impacts on ecosystems include shifts in species ranges, altered phenology, and changes in ecosystem structure and function
  • Many species are migrating to higher latitudes or elevations in response to warming temperatures
• Extreme weather events, such as heatwaves, droughts, and intense precipitation, are expected to become more frequent and severe
• Ocean acidification occurs as the ocean absorbs excess atmospheric CO2, lowering the pH of seawater
  • Acidification can impair the ability of marine organisms to build calcium carbonate shells and skeletons

Monitoring and Measurement Techniques

• Ground-based monitoring stations measure pollutant concentrations at specific locations
  • The US EPA's Air Quality System (AQS) collects data from a network of monitoring stations
• Satellite remote sensing provides global coverage and can measure pollutants in the atmosphere
  • Instruments like OMI (Ozone Monitoring Instrument) and MODIS (Moderate Resolution Imaging Spectroradiometer) measure various pollutants
• Lidar (Light Detection and Ranging) uses laser pulses to measure the vertical distribution of pollutants and aerosols
• Chemiluminescence analyzers measure NO and NO2 concentrations by detecting light emitted from the reaction of NO with ozone
• UV fluorescence analyzers measure SO2 concentrations based on the fluorescence of SO2 molecules when exposed to UV light
• Beta attenuation monitors measure PM concentrations by detecting the absorption of beta radiation by particles
• Passive sampling techniques use diffusive samplers to measure average pollutant concentrations over a period of time
• Grab sampling involves collecting a sample of air at a specific time and location for later analysis

Pollution Control Strategies

• Emission standards set limits on the amount of pollutants that can be released from specific sources (vehicles, power plants)
  • The US Clean Air Act sets National Ambient Air Quality Standards (NAAQS) for criteria pollutants
• Fuel quality improvements, such as reducing sulfur content in diesel fuel, can lower emissions of SO2 and PM
• Renewable energy sources, like solar and wind power, can reduce emissions from fossil fuel combustion
• Energy efficiency measures in buildings, transportation, and industry can reduce energy consumption and associated emissions
• Catalytic converters in vehicles convert pollutants (CO, NOx, and VOCs) into less harmful compounds
• Scrubbers in industrial facilities remove pollutants, such as SO2 and PM, from exhaust gases
  • Wet scrubbers use a liquid solution to absorb pollutants
  • Dry scrubbers use a dry sorbent, such as limestone, to remove pollutants
• Electrostatic precipitators (ESPs) use an electric field to remove PM from exhaust gases in industrial processes
• Carbon capture and storage (CCS) technologies aim to capture CO2 emissions from power plants and industrial facilities and store them underground