Air Pollutants, Risk Assessment & Carbon Monoxide – Lecture Vocabulary

Risk Assessment in Air-Pollution Science

• Risk assessment = data–driven forecasting and decision making
  • Must rely on measured scientific evidence, not opinion or political rhetoric.
  • Sequence:
  1. Collect & evaluate data ("seismic" = solid, objective).
  2. Make organized probabilistic predictions (5, 10, 20-year horizons, etc.).
  • Ethic of science: never declare “dangerous” or “safe” without quantitative support.

Two Determining Factors of Health Risk

• 1. Toxicity
  • Intrinsic hazard of the substance.
  • Example: Lead – dangerous even at trace levels.
• 2. Exposure
  • Duration / concentration of contact.
  • Even low-toxicity species become harmful with prolonged or high exposure.
• Classical summary (Paracelsus):
  • “All things are poison and nothing is without poison; only the dose makes the poison.”
  • Emphasizes the combined role of toxicity and exposure.

Primer on Key Mobile-Source Pollutants

• Monitored vehicle-emission species (lecture graph)
  • Hydrocarbons (HC)
  • Carbon monoxide (CO)
  • Nitrogen oxides (NO$_x$, where x = 1 or 2)
  • Sometimes sulfur oxides written SO$_x$ (x = 2 or 3).
  • Each has a green horizontal "standard" line indicating legal/health limit — except CO$_2$.
  • Reason: regular ambient CO$_2$ is not acutely toxic at environmental levels; thus no short-term health standard plotted.

Carbon Monoxide (CO) – Focus Pollutant

• Properties
  • Colorless, odorless → "silent killer" (cannot be detected by human senses).
• Formation
  • Incomplete combustion in gasoline engines if O$_2$ supply or engine tuning is insufficient.
• Health Mechanism
  • CO diffuses into bloodstream → binds hemoglobin (Hb) to form carboxyhemoglobin.
  • Hb then can no longer transport O$_2$ → cellular hypoxia → organ failure → death.
• Regulatory limit (indoor/ambient)
  • 9\,\text{ppm} (parts per million) acceptable average.
  • Conversion to percent: 9\,\text{ppm}=\frac{9}{10\,000}\%=9\times10^{-4}\% (shows how tiny the lethal fraction can be).
• Necessity of CO detectors in homes & enclosed spaces; ensure batteries/functionality.

Catalytic Converters – Chemical Solution in Automobiles

• Purpose: turn harmful exhaust into less harmful gases.
• Key reactions
  1. 2\,\text{CO}+\text{O}2\;\xrightarrow{\text{catalyst}}\;2\,\text{CO}2
  2. 2\,\text{NO}x\;\xrightarrow{\text{catalyst}}\;\text{N}2+\text{O}_2
  3. Partial oxidation of volatile organic compounds (VOCs).
• Catalyst composition
  • Precious metals: Platinum (Pt), Rhodium (Rh) (illustrates Chapter-1 theme: strategic value of metals).
• Definition (for later chapters):
  • Catalyst = substance that participates in a reaction and speeds it up without being consumed.
• Broader lesson: Chemistry is both part of the problem and the solution.

Worked Quantitative Example (Classroom Problem)

• Given: One breath contains 2.0\times10^{22} total molecules/atoms.
• Standard: 9\,\text{ppm}\;(=9\times10^{-6}) CO.
• Find CO molecules per breath.
• Setup (unit-conversion, 1 step):
  \left(2.0\times10^{22}\;\frac{\text{molecules}}{\text{breath}}\right)\times\left(\frac{9\,\text{CO molecules}}{1\times10^{6}\,\text{total molecules}}\right)=1.8\times10^{17}\;\text{CO molecules/breath}
• Illustrates ppm as "x per million" parts.

Additional Context & Takeaways

• Rising CO$_2$ concentration is an environmental/climate issue, not an acute toxicity issue at atmospheric levels.
• Extremely small concentration changes (sub-ppm) can have life-or-death implications for toxic gases like CO.
• Maintaining natural atmospheric balance is critical—human perturbations at the ppm level can cascade into health crises.
• Ethical responsibility: Scientists must quantify, communicate, and engineer solutions (e.g., catalytic converters) rather than rely on anecdotal claims.

Key Numbers & Conversions Recap

• 1\,\text{ppm}=1\text{ part per }10^{6}\text{ parts}
• Percent ↔ ppm conversion: 1\% =10\,000\,\text{ppm} (factor 10^{4}).
• Acceptable indoor CO: 9\,\text{ppm}=9\times10^{-4}\%.
• CO molecules in a normal breath at this limit: 1.8\times10^{17}.

Connections & Real-World Relevance

• Combustion chemistry intertwines with public health, automotive engineering, and environmental policy.
• Risk-assessment framework here mirrors approaches in climate modeling, toxicology, pharmaceutical dosing, etc.
• The Paracelsian “dose makes the poison” principle underpins regulatory toxicology and drug safety alike.
• Precious-metal demand for catalytic converters links environmental regulation to global mining practices (resource management ethics).

Study Tips

• Memorize the two risk factors and be able to apply them to any pollutant.
• Practice ppm ↔ percent ↔ molecules conversions until automatic.
• Understand how catalytic converters simultaneously address CO, NO$_x$, and VOCs; sketch the reaction pathways.
• Be prepared to explain why CO$_2$ lacks a short-term health standard yet remains environmentally significant.
• Recall the physiological action of CO on hemoglobin for potential short-answer questions.