ChemistryChapter 13: Environmental Chemistry-Air
Smog, Acid Rain, Aqi
Smog is polluted atmospheric haze formed from mixtures of pollutants.
Definition
Smog is polluted atmospheric haze formed from mixtures of pollutants. Acid rain is precipitation made unusually acidic mainly because sulphur dioxide and nitrogen oxides form acidic compounds in the atmosphere. AQI, or Air Quality Index, is a system used to report the level of air pollution.
Core Concept
These three terms are related to air pollution but describe different things. Smog = polluted atmosphere. Acid rain = acidic deposition. AQI = pollution reporting index. They must never be treated as the same concept.
Beginner
Smog means dirty polluted air. Acid rain happens when pollution gases form acids in the atmosphere. AQI tells people how polluted the air is.
Intermediate
Smog and acid rain are environmental processes. AQI is a measurement/reporting tool. Photochemical smog depends strongly on atmospheric reactions driven by sunlight. Acid rain depends mainly on acid-forming pollutants such as SO₂ and NOₓ.
Advanced
Smog and acid deposition involve different reaction networks. Photochemical smog is dominated by sunlight-driven oxidation chemistry that can produce secondary oxidants such as O₃. Acid deposition results from atmospheric transformation of sulphur and nitrogen compounds into more strongly acidic species. AQI does not describe one specific chemical reaction; it summarizes measured air-quality data for communication and health awareness.
Important Formula / Equation
Sulphur oxidation: 2SO₂ + O₂ → 2SO₃ Acid formation: SO₃ + H₂O → H₂SO₄ Photochemical-smog idea: NOₓ + VOCs + sunlight → secondary pollutants
Remember / Key Reminder
Smog = polluted haze. Photochemical smog needs sunlight. SO₂ and NOₓ contribute to acid rain. CO₂ is not the principal conventional cause of acid rain. AQI = Air Quality Index. AQI is not a gas or chemical pollutant. Ground-level O₃ can form in photochemical smog.
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Smog, Acid Rain, Aqi
Sticky Notes · Quick Revision
Memory Point 1
- Smog = polluted haze
Memory Point 2
- Sunlight drives photochemical smog
Memory Point 3
- NOₓ = smog precursor
Memory Point 4
- VOCs participate in smog chemistry
Memory Point 5
- SO₂ → acid deposition
Memory Point 6
- NOₓ → acid deposition
Memory Point 7
- AQI = Air Quality Index
Memory Point 8
- AQI ≠ pollutant
60-second revision
- Smog is polluted atmospheric haze, while photochemical smog forms through sunlight-driven reactions involving NOₓ and organic pollutants. Acid rain is mainly linked to SO₂ and NOₓ. AQI is an index used to communicate air-quality conditions.
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