7.2 - Photochemical Smog

Question 1

Photochemical Smog Precursors

Answer 1

• NO2 - brokn by sunlight into NO + O (free O+O2= O3)
• VOCs - Volatile Organic Compounds (hydrocarbons) that bind with NO and form photochemical oxidants
  - carbon based compounds that volatize (evaporate) easily (this maeks them “smely)
  - sources: gasoline, formaldehyde, cleaning fluids, oil-based paints, even coniferous trees (pine smell)
• O3 - fors when NO2 is broken by sunlight and free O binds to O2
  - respiratory irritant in troposphere
  - damaging to plantstomata, limiting growth

Question 2

Photochemical smog conditions

Answer 2

• sunlight - drices O3 formation by breaking down NO2 - No + O; then free O atom binds with O2
• Warmth - hotter atmospheric temperature speeds O3 formation, evaporation of VOCs and thus smog formation

Question 3

Normal O3 Formation

Answer 3

• NO2 -> NO + O; O3+ NO -> O2 and NO2
• Snlight breaks NO2 into NO + O; O bonds with O2 to form O3
  Steps:
• Morning commute leads to high NO2 levels from car exhaust
• O3 formation typically peaks in afternoon when sunight is most direct and NO2 emissions from morning traffic have peaked
• At night, O3 reacts with NO to form NO2 and O2 once again, O3 levels drop overnight

Question 4

Photochemical Smog Formation

Answer 4

• NO2 -> NO + O; O+O2 -> O3
• Sunlight breaks NO2 into NO+O; O bons with O2 to form O3

Steps:
- Morning commute leads to high NO2 levels from car exhaust
- O3 formation typically peaks in afternoon when sunight is most direct and NO2 emissions from morning traffic have peaked
VOCs bond with NO to form photochemical oxidants
- O3 combines with Photochemical oxidants (NO + VOCs) ro form photochemical smog
- Without NO to react with, O3 builds up instead of returning to O2 and NO2 overnight

Question 5

Factors that increase Smog Formation

Answer 5

• More sunlight = More O3
• Warmer Temperature, speedse vapporation of VOCs and rxn that lead to O3
• Hgher VOCs emissions (gas stations, laundromats, petrochemicals, and plastic factories)
• Increased Vehicle Traffic; increases NO2 emissions and therefore O3 formation
• Urban areas have more smog due to all of these factors
  - more trafic = more NO2
  - hotter temps due to low albedo of blacktop
  -More VOCs dueto gas stations and factories
  - More elctricity demand; more NOx emissions from nearby power plants

Question 6

Impacts of Smog

Answer 6

Environmental:
- Reduces sunlight limiting photosynthesis
- O3 damages plant stomata and irritates snimal respiratory tracts

Humans:
- Respiratory irritant
- worsens asthma
- bronchitis
COPD

Economic:
- Increased health care coststo treat asthma, bronchitis, COPD
- lost productivity due to sick workers missing work or dying
- Decreased agricultural yields due to less sunlight reaching crops and damage to plant stomata

Question 7

Reduction of Smog

Answer 7

Vehicles:
- Decreasing the number of vehicles on the road decreases NO2 emissions
- fewer vehicles = less gas = fewer VOCs
- Carpooling, public transporation, biking, walking, working from home

Energy:
- increased electricity production from renewable sorces that don’t emit NOx(solar, wind, hydro)
- natural gas power plants release far less NOx than coal