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:
- Collect & evaluate data ("seismic" = solid, objective).
- 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
- 2\,\text{CO}+\text{O}2\;\xrightarrow{\text{catalyst}}\;2\,\text{CO}2
- 2\,\text{NO}x\;\xrightarrow{\text{catalyst}}\;\text{N}2+\text{O}_2
- 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.