AQS Pollution Sources 3 — Questions and Answers
Question 1: Which industrial process is the dominant anthropogenic source of sulfur dioxide (SO2) emissions in the United States?
- Natural gas processing
- Fossil fuel combustion at electric utilities (Correct answer)
- Motor vehicle exhaust
- Agricultural tillage
Correct answer: Fossil fuel combustion at electric utilities
Electric utility fossil fuel combustion, especially from coal-fired power plants, historically accounts for the largest share of U.S. SO2 emissions.
Question 2: Biogenic VOC emissions from vegetation are significant because they contribute to the formation of which secondary pollutant?
- Carbon monoxide
- Tropospheric ozone (Correct answer)
- Sulfuric acid aerosol
- Mercury vapor
Correct answer: Tropospheric ozone
Biogenic VOCs such as isoprene react with nitrogen oxides in the presence of sunlight to form ground-level ozone.
Question 3: A petroleum refinery that processes more than 10 tons per year of a single HAP is classified under the CAA as a:
- Minor source
- Title V major source (Correct answer)
- Area source
- Emergency generator
Correct answer: Title V major source
Under Title V, sources emitting 10 tpy or more of a single HAP (or 25 tpy of combined HAPs) are classified as major sources subject to operating permit requirements.
Question 4: Which sector is the leading source of NOx emissions in the U.S. according to the National Emissions Inventory?
- Highway mobile sources (Correct answer)
- Industrial boilers
- Wildfires
- Agricultural fertilizer application
Correct answer: Highway mobile sources
Highway mobile sources, including cars, trucks, and buses, are consistently the largest contributor to NOx emissions nationally.
Question 5: Chromate cooling towers at industrial facilities are regulated air emission sources primarily because they release:
- Carbon monoxide
- Hexavalent chromium (Cr VI) as a toxic aerosol (Correct answer)
- Ammonia
- Nitrogen trifluoride
Correct answer: Hexavalent chromium (Cr VI) as a toxic aerosol
Chromate cooling towers emit hexavalent chromium droplets into the air, a known human carcinogen regulated under the NESHAP program.
Question 6: Secondary organic aerosols (SOA) differ from primary particulate matter in that they:
- Are emitted directly from combustion stacks
- Form in the atmosphere through chemical reactions of gaseous precursors (Correct answer)
- Only originate from sea spray
- Are larger than PM10 particles
Correct answer: Form in the atmosphere through chemical reactions of gaseous precursors
SOA forms in the atmosphere when VOCs and other organic gases oxidize and condense, making them a secondary rather than directly emitted pollutant.
Question 7: What is the principal air quality concern associated with confined animal feeding operations (CAFOs)?
- Ozone depletion
- Ammonia and hydrogen sulfide emissions causing PM and odor impacts (Correct answer)
- Mercury bioaccumulation in air
- Radioactive particle release
Correct answer: Ammonia and hydrogen sulfide emissions causing PM and odor impacts
CAFOs emit ammonia (which forms secondary PM2.5) and hydrogen sulfide, causing both regulatory and community health concerns.
AQS Pollution Sources 3
Which industrial process is the dominant anthropogenic source of sulfur dioxide (SO2) emissions in the United States?