2.3 Atmospheric chemistry and air pollution

Air pollution and atmospheric chemistry are crucial aspects of our environment. They impact human health, ecosystems, and climate. Understanding how pollutants form, spread, and interact helps us grasp the complexity of air quality issues and their far-reaching effects.

From industrial emissions to vehicle exhaust, human activities significantly alter atmospheric composition. This knowledge drives efforts to reduce pollution through regulations, clean technologies, and urban planning. It also highlights the need for global cooperation to address air quality challenges that cross borders.

Formation and effects of air pollutants

Tropospheric ozone and particulate matter

Top images from around the web for Tropospheric ozone and particulate matter

• 

  Ozone | Environment, land and water | Queensland Government View original

  Is this image relevant?

• 

  ESS Topic 6.3: Photochemical Smog - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  ACP - Arctic tropospheric ozone: assessment of current knowledge and model performance View original

  Is this image relevant?

• 

  Ozone | Environment, land and water | Queensland Government View original

  Is this image relevant?

• 

  ESS Topic 6.3: Photochemical Smog - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

1 of 3

Top images from around the web for Tropospheric ozone and particulate matter

• 

  Ozone | Environment, land and water | Queensland Government View original

  Is this image relevant?

• 

  ESS Topic 6.3: Photochemical Smog - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

• 

  ACP - Arctic tropospheric ozone: assessment of current knowledge and model performance View original

  Is this image relevant?

• 

  Ozone | Environment, land and water | Queensland Government View original

  Is this image relevant?

• 

  ESS Topic 6.3: Photochemical Smog - AMAZING WORLD OF SCIENCE WITH MR. GREEN View original

  Is this image relevant?

1 of 3

• Tropospheric ozone (O₃) forms through complex photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) in sunlight
  • NOx and VOCs react in a series of steps, producing ozone as a secondary pollutant
  • Ozone concentrations typically peak during hot, sunny afternoons
• Particulate matter (PM) consists of solid and liquid particles suspended in air
  • Categorized by size: PM10 (diameter < 10 μm), PM2.5 (diameter < 2.5 μm)
  • Composition varies: sulfates, nitrates, organic compounds, metals
• Ozone acts as a powerful oxidant in the troposphere
  • Causes respiratory issues in humans (coughing, throat irritation, reduced lung function)
  • Damages vegetation by interfering with photosynthesis and reducing crop yields
• Fine particulate matter (PM2.5) poses significant health risks
  • Penetrates deep into lungs and bloodstream
  • Leads to cardiovascular and respiratory diseases (asthma, heart attacks, lung cancer)
  • Reduces visibility in urban areas, creating haze

Acid rain formation and impacts

• Acid rain forms when sulfur dioxide (SO₂) and nitrogen oxides (NOx) react with atmospheric water, oxygen, and other chemicals
  • SO₂ + H₂O → H₂SO₃ (sulfurous acid)
  • 2NO₂ + H₂O → HNO₂ (nitrous acid) + HNO₃ (nitric acid)
• Alters pH of water bodies and soils
  • Acidifies lakes and streams, harming aquatic life (fish, amphibians)
  • Leaches nutrients from soil, impacting forest health and agricultural productivity
• Accelerates weathering of buildings and monuments
  • Corrodes metal structures (bridges, statues)
  • Erodes limestone and marble facades (historical buildings)

Meteorological influences on pollutant formation and transport

• Temperature affects reaction rates and pollutant formation
  • Higher temperatures generally increase ozone production
  • Inversions trap pollutants near the ground, exacerbating air quality issues
• Humidity influences particulate matter concentrations
  • High humidity can lead to hygroscopic growth of particles, increasing their size and effects
• Wind patterns determine pollutant dispersion and transport
  • Strong winds can dilute local pollution but may carry pollutants to distant areas
  • Sea breezes in coastal areas can recirculate pollutants, creating persistent pollution episodes
• Atmospheric stability impacts vertical mixing of pollutants
  • Stable conditions (little vertical mixing) trap pollutants near the surface
  • Unstable conditions promote dispersion but can also lead to convective transport of pollutants to higher altitudes

Sources of anthropogenic air pollution

Industrial and energy sector emissions

• Fossil fuel combustion in power plants and industrial facilities releases major pollutants
  • Sulfur dioxide (SO₂) from coal and oil burning
  • Nitrogen oxides (NOx) from high-temperature combustion processes
  • Carbon dioxide (CO₂) as a primary greenhouse gas
• Industrial processes contribute various toxic air pollutants
  • Volatile organic compounds (VOCs) from chemical manufacturing and solvent use
  • Heavy metals (mercury, lead) from metal production and waste incineration
  • Particulate matter from mining, construction, and manufacturing activities
• These emissions impact human health and the environment
  • Respiratory diseases (asthma, bronchitis) from long-term exposure to SO₂ and NOx
  • Acid rain formation affecting ecosystems and infrastructure
  • Climate change driven by increasing CO₂ concentrations

Transportation and urban pollution sources

• Vehicles are major contributors to urban air pollution
  • Nitrogen oxides (NOx) and particulate matter from diesel engines
  • Carbon monoxide (CO) and VOCs from gasoline engines
  • Ground-level ozone formation from NOx and VOC reactions in sunlight
• Urban areas concentrate pollution sources
  • High density of vehicles, buildings, and industrial activities
  • Formation of urban heat islands, exacerbating ozone production
  • Reduced air circulation due to building structures, trapping pollutants
• Long-term exposure in urban environments increases health risks
  • Higher rates of cardiovascular problems (heart disease, stroke)
  • Increased incidence of certain cancers (lung, bladder)
  • Cognitive decline and neurodegenerative diseases linked to air pollution exposure

Agricultural and biomass burning emissions

• Agricultural activities release various air pollutants
  • Ammonia (NH₃) from livestock waste and fertilizer application
  • Methane (CH₄) from ruminant animals (cattle, sheep) and rice cultivation
  • Nitrous oxide (N₂O) from soil management and fertilizer use
• Biomass burning contributes to air pollution
  • Forest fires release large amounts of particulate matter and carbon monoxide
  • Agricultural waste burning emits black carbon and organic compounds
  • Slash-and-burn practices in tropical regions contribute to regional haze episodes
• These sources impact both local air quality and global atmospheric composition
  • Ammonia contributes to secondary particulate matter formation
  • Methane and nitrous oxide are potent greenhouse gases
  • Biomass burning emissions can be transported long distances, affecting air quality in distant regions

Atmospheric pollutants: formation and destruction

Nitrogen and sulfur cycles in the atmosphere

• Nitrogen cycle involves complex reactions between various nitrogen oxides (NOx)
  • NO + O₃ → NO₂ + O₂ (conversion of nitric oxide to nitrogen dioxide)
  • NO₂ + hν → NO + O (photolysis of nitrogen dioxide)
  • O + O₂ + M → O₃ + M (ozone formation, where M is a third body)
• NOx plays a crucial role in ozone formation and acid rain production
  • Catalyzes ozone formation in the presence of VOCs and sunlight
  • Contributes to nitric acid formation in the atmosphere
• Sulfur cycle includes oxidation of sulfur dioxide (SO₂) to sulfuric acid (H₂SO₄)
  • SO₂ + OH + M → HSO₃ + M (initial step in SO₂ oxidation)
  • HSO₃ + O₂ → SO₃ + HO₂ (formation of sulfur trioxide)
  • SO₃ + H₂O → H₂SO₄ (rapid conversion to sulfuric acid)
• Sulfuric acid is a key component of acid rain and secondary particulate matter
  • Forms sulfate aerosols, contributing to PM2.5 concentrations
  • Participates in cloud condensation nuclei formation, affecting cloud properties

Photochemical reactions and smog formation

• Photochemical smog formation involves a series of reactions initiated by NO₂ photolysis
  • NO₂ + hν → NO + O (wavelengths < 420 nm)
  • O + O₂ + M → O₃ + M
  • O₃ + NO → NO₂ + O₂ (ozone destruction by NO)
• VOCs play a crucial role in sustaining ozone production
  • RH + OH → R + H₂O (initial VOC oxidation, where RH is a hydrocarbon)
  • R + O₂ + M → RO₂ + M (formation of peroxy radicals)
  • RO₂ + NO → RO + NO₂ (conversion of NO to NO₂ without consuming ozone)
• Secondary pollutants formed in photochemical smog
  • Peroxyacetyl nitrate (PAN), a strong eye irritant and phytotoxin
  • Formaldehyde (HCHO) and other aldehydes
  • Secondary organic aerosols (SOA) from VOC oxidation products

Oxidation processes and the role of the hydroxyl radical

• Hydroxyl radical (OH) serves as the primary oxidant in the troposphere
  • Formed primarily through ozone photolysis and subsequent reaction with water vapor $O₃ + hν → O(¹D) + O₂$ $O(¹D) + H₂O → 2OH$
  • Initiates the breakdown of many pollutants and greenhouse gases $CH₄ + OH → CH₃ + H₂O$ (methane oxidation) $CO + OH → CO₂ + H$ (carbon monoxide oxidation)
• VOCs undergo oxidation reactions in the atmosphere
  • Multi-step processes involving OH, NO₃, and O₃ as oxidants
  • Leads to the formation of more oxidized, less volatile compounds
  • Contributes to secondary organic aerosol (SOA) formation
• Heterogeneous reactions occur on aerosol and cloud droplet surfaces
  • N₂O₅ + H₂O(aq) → 2HNO₃ (nitric acid formation on aqueous surfaces)
  • SO₂ + H₂O₂(aq) → H₂SO₄ (sulfuric acid formation in cloud droplets)
  • These reactions can significantly affect pollutant chemistry and lifetime

Strategies for mitigating air pollution

Regulatory and technological approaches

• Implementation of stringent emission standards for industries, vehicles, and power plants
  • Best Available Control Technology (BACT) requirements for new sources
  • Continuous Emission Monitoring Systems (CEMS) for real-time pollution tracking
• Promotion of clean energy technologies to decrease reliance on fossil fuels
  • Renewable energy sources (solar, wind, geothermal)
  • Energy-efficient systems in buildings and industrial processes
• Development and adoption of cleaner transportation options
  • Electric vehicles and charging infrastructure
  • Improved public transit systems (bus rapid transit, light rail)
  • Active transportation infrastructure (bike lanes, pedestrian-friendly streets)
• Application of air pollution control technologies
  • Scrubbers for removing SO₂ from power plant emissions
  • Catalytic converters in vehicles to reduce NOx and CO emissions
  • Particulate filters for diesel engines to capture fine particles

Urban planning and air quality management

• Implementation of urban planning strategies to reduce air pollution
  • Creating green spaces to improve air quality and reduce urban heat island effect
  • Improving building energy efficiency through better insulation and HVAC systems
  • Promoting compact city designs to reduce transportation emissions
• Utilization of air quality monitoring networks and forecasting systems
  • Dense networks of sensors for real-time pollution data collection
  • Integration of satellite observations for broader spatial coverage
  • Advanced modeling techniques for accurate air quality predictions
• Public awareness and education programs
  • Air quality index (AQI) reporting to inform the public about pollution levels
  • Health advisories during high pollution episodes
  • Promotion of individual actions to reduce personal contributions to air pollution

International cooperation and global initiatives

• International agreements to address transboundary air pollution issues
  • Convention on Long-Range Transboundary Air Pollution (CLRTAP)
  • Regional efforts like the ASEAN Agreement on Transboundary Haze Pollution
• Global atmospheric chemistry challenges addressed through international cooperation
  • Montreal Protocol for phasing out ozone-depleting substances
  • Paris Agreement for reducing greenhouse gas emissions and combating climate change
• Collaborative research initiatives to improve understanding of atmospheric processes
  • Global Atmosphere Watch (GAW) program for long-term monitoring of atmospheric composition
  • International Global Atmospheric Chemistry (IGAC) project for coordinating research efforts
• Technology transfer and capacity building in developing countries
  • Sharing best practices for air quality management
  • Financial and technical assistance for implementing clean technologies