AQS Mitigation Strategies 2 — Questions and Answers
Question 1: Which control technology is most effective for reducing fine particulate matter (PM2.5) from industrial stack emissions?
- Cyclone separator
- Fabric filter (baghouse) (Correct answer)
- Settling chamber
- Spray tower
Correct answer: Fabric filter (baghouse)
Fabric filters (baghouses) achieve collection efficiencies above 99% for PM2.5 and are among the most effective controls for fine particulate emissions.
Question 2: An industrial facility installs a regenerative thermal oxidizer (RTO). What pollutant class does this primarily control?
- Nitrogen oxides (NOx)
- Volatile organic compounds (VOCs) (Correct answer)
- Sulfur dioxide (SO2)
- Heavy metals
Correct answer: Volatile organic compounds (VOCs)
RTOs combust VOCs at high temperatures (typically 1,400–1,600°F) with heat recovery efficiencies of 95% or more.
Question 3: Selective catalytic reduction (SCR) systems inject which reagent to reduce NOx emissions?
- Activated carbon
- Ammonia or urea (Correct answer)
- Lime slurry
- Hydrogen peroxide
Correct answer: Ammonia or urea
SCR systems inject ammonia (or urea that hydrolyzes to ammonia) into flue gas where it reacts with NOx over a catalyst to form N₂ and H₂O.
Question 4: What is the primary purpose of a flue gas desulfurization (FGD) scrubber in a coal-fired power plant?
- Remove NOx via catalytic reduction
- Capture SO2 using an alkaline sorbent (Correct answer)
- Reduce carbon monoxide through oxidation
- Filter mercury using activated carbon
Correct answer: Capture SO2 using an alkaline sorbent
FGD scrubbers react SO2 in flue gas with an alkaline reagent such as limestone slurry, forming calcium sulfite or gypsum as a byproduct.
Question 5: In transportation air quality planning, Transportation Demand Management (TDM) reduces emissions primarily by:
- Switching fleet vehicles to lower-emission fuels
- Reducing the number of vehicle miles traveled (VMT) (Correct answer)
- Installing catalytic converters on existing vehicles
- Widening highways to reduce congestion
Correct answer: Reducing the number of vehicle miles traveled (VMT)
TDM strategies such as ridesharing, telecommuting, and transit incentives aim to reduce VMT, thereby cutting total mobile-source emissions.
Question 6: A low-sulfur fuel requirement is an example of which mitigation approach category?
- Add-on control technology
- Pollution prevention / source reduction (Correct answer)
- Dispersion enhancement
- Biological treatment
Correct answer: Pollution prevention / source reduction
Switching to low-sulfur fuel reduces sulfur at the source before combustion, qualifying it as a pollution prevention or process change strategy.
Question 7: Which street-level urban design strategy most directly reduces photochemical smog precursor emissions from motor vehicles?
- Widening arterial roads to increase speed
- Implementing traffic signal synchronization ('green waves') (Correct answer)
- Raising posted speed limits on freeways
- Installing concrete median barriers
Correct answer: Implementing traffic signal synchronization ('green waves')
Signal synchronization reduces stop-and-go driving, lowering vehicle idle time and thus cutting VOC and NOx emissions that form ozone.
AQS Mitigation Strategies 2
Which control technology is most effective for reducing fine particulate matter (PM2.5) from industrial stack emissions?