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 ppm 9\,\text{ppm} 9 ppm Conversion to percent: 9 ppm = 9 10 000 % = 9 × 10 − 4 % 9\,\text{ppm}=\frac{9}{10\,000}\%=9\times10^{-4}\% 9 ppm = 10 000 9 % = 9 × 1 0 − 4 % 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 CO + O < e m > 2 → catalyst 2 CO < / e m > 2 2\,\text{CO}+\text{O}<em>2\;\xrightarrow{\text{catalyst}}\;2\,\text{CO}</em>2 2 CO + O < e m > 2 catalyst 2 CO < / e m > 2 2 NO < e m > x → catalyst N < / e m > 2 + O 2 2\,\text{NO}<em>x\;\xrightarrow{\text{catalyst}}\;\text{N}</em>2+\text{O}_2 2 NO < e m > x catalyst N < / e m > 2 + 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 × 10 22 2.0\times10^{22} 2.0 × 1 0 22 Standard: 9 ppm ( = 9 × 10 − 6 ) 9\,\text{ppm}\;(=9\times10^{-6}) 9 ppm ( = 9 × 1 0 − 6 ) Find CO molecules per breath. Setup (unit-conversion, 1 step):( 2.0 × 10 22 molecules breath ) × ( 9 CO molecules 1 × 10 6 total molecules ) = 1.8 × 10 17 CO molecules/breath \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} ( 2.0 × 1 0 22 breath molecules ) × ( 1 × 1 0 6 total molecules 9 CO molecules ) = 1.8 × 1 0 17 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 ppm = 1 part per 10 6 parts 1\,\text{ppm}=1\text{ part per }10^{6}\text{ parts} 1 ppm = 1 part per 1 0 6 parts Percent ↔ ppm conversion: 1 % = 10 000 ppm 1\% =10\,000\,\text{ppm} 1% = 10 000 ppm 10 4 10^{4} 1 0 4 Acceptable indoor CO: 9 ppm = 9 × 10 − 4 % 9\,\text{ppm}=9\times10^{-4}\% 9 ppm = 9 × 1 0 − 4 % CO molecules in a normal breath at this limit: 1.8 × 10 17 1.8\times10^{17} 1.8 × 1 0 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.