Sources
Identify two primary pollutants commonly emitted by fossil-fuel combustion.
NOx and SO2
These pollutants are emitted directly during combustion of coal/oil/gas and are not formed later in the atmosphere.
Which two pollutants are most responsible for photochemical smog formation?
NOx and VOCs
NOx and VOCs react in sunlight to produce ozone and other oxidants that make photochemical smog.
What is the approximate pH of acid rain?
~4.3
Acid rain is more acidic than normal rain (~5.6) due to added nitric and sulfuric acids.
Name one technology used to reduce NOx emissions from vehicles.
Catalytic Converters
Catalysts promote reactions that convert NOx to nitrogen gas (N₂), reducing NOx in exhaust.
What do CAFE standards regulate?
Fuel economy (mpg)
Higher fuel economy reduces fuel burned and can reduce emissions associated with driving.
A city bans wood-burning fireplaces on high-pollution days. Which pollutant is this most directly targeting, and why?
PM2.5 (fine particulate matter)
Wood smoke contains high levels of fine particles that penetrate deep into lungs and also reduce visibility.
Why is ozone typically higher downwind of a city than in the city center?
Ozone forms after transport and reaction time
NOx/VOCs need time and sunlight to react; wind carries precursors downwind where ozone accumulates
Explain how NOx can lead to nitric acid formation in the atmosphere?
NOx + O₂ + H₂O → HNO₃
Nitrogen oxides react in the atmosphere to form nitric acid, a major component of acid deposition.
Which smokestack technology best removes particulate matter and how does it work?
Electrostatic precipitator or baghouse filter
These devices capture particles by charging/attracting them (precipitator) or filtering them through fabric (baghouse).
Explain one reason leaded gasoline was phased out.
Health harm and it damaged catalytic converters
Lead is a neurotoxin and also ‘poisoned’ catalytic converters, reducing their ability to control exhaust pollutants.
Explain why NOx emissions increase when combustion temperatures are very high
High-temperature combustion forms NOx
At high temperatures, nitrogen (N₂) and oxygen (O₂) in air react to form NO and NO₂ (NOx).
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Explain how sunlight promotes ozone formation from NO2
UV splits NO2, then forms O3
Sunlight photolyzes NO2--> NO+O; the free O atom combines with O2 to make ozone
Explain how limestone can reduce damage from acid deposition in soils/lakes.
Limestone buffers acids
Calcium carbonate neutralizes acids, raising pH and reducing toxicity from mobilized metals like aluminum.
Explain how a catalytic converter reduces multiple pollutants.
Catalyzes redox reactions
It converts NOx → N₂ and oxidizes CO/VOCs → CO₂ + H₂O, reducing several harmful pollutants.
Explain how CAFE standards can indirectly reduce photochemical smog.
Less fuel burned → fewer precursors
Better fuel efficiency can reduce NOx/VOC emissions per mile and supports cleaner vehicle technologies.
Predict what happens to ground-level ozone on hot sunny days with heavy traffic, and explain using NOx + VOC chemistry.
Ozone levels increase
Traffic emits NOx and VOCs; sunlight drives photochemical reactions that create O₃ (a secondary pollutant).
A city reduces VOC emissions but NOx stays constant. Predict the likely effect on ozone formation and justify
Ozone formation often decreases
With fewer VOCs, a key reactant is limited, so photochemical ozone production is reduced even if NOx remains
A lake’s pH drops from 6.8 to 5.2 after repeated acid deposition. Predict two ecological impacts and explain.
Reduced fish/invertebrate survival; increased metal toxicity
Low pH stresses organisms (eggs, gills) and increases dissolved Al³⁺, which is harmful to many aquatic species.
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Which strategy reduces air pollution more reliably—end-of-pipe controls or source reduction? Defend
Source reduction is typically more effective long-term
Preventing emissions (renewables, efficiency) reduces pollution at the source; controls help but don’t eliminate fossil fuel reliance.
Propose one policy to reduce urban ozone and explain the mechanism.
Reduce NOx/VOC emissions via policy
Policies like stricter emissions standards, VOC limits, transit investment, or congestion pricing reduce ozone precursors.