APES Unit 7.2 Photochemical Smog

Practice FRQ

● Explain the relationship between NO2 concentration and ozone concentration represented in this graph

● Describe how the time of day impacts ozone formation.

NO2 and ozone increase together until 9 am as NO2 drops and ozone peaks at 2 pm. This is because ozone accumulates through an abundance of nitrogen dioxides and sunlight. So, into the afternoon, ozone increases, but when daylight decreases, ozone drops too.

Photochemical Smog

AKA BROWN SMOG—A complex combination of compounds and it can be reduced by decreasing emissions of its precursors

What is Smog Responsible For?

Hazy view and reduced sunlight in many cities

• Ozone (O3)

Smog

1. Photochemical Smog

2. Sulfur Smog

Photochemical smog is dominated by…

oxidants

• ozone

3 Elements of Photochemical Smog

1. Sunlight

2. Water

3. VOCs

What Leads to Ozone Accumulation

abundance of nitrogen dioxide in the atmosphere + sunlight and warms the atmosphere

3 Extra Contributions to Photochemical Smog

• Forest fires also contribute to the poor air quality

• Ozone concentrations are the highest during the middle of the day and during the summer months

• Acts on vehicle/industrial emission

Sulfur Smog

London-type smog, gray smog, or industrial smog—Dominated by sulfur dioxide, sulfate compounds, and particulate matter

• in cool, humid, industrial conditions unlike photochemical smog

Economic Harm from Sulfur Smog

• Poor visibility can reduce tourism

• Lower revenue for recreation area (hotels and restaurants)

VOCs

Formed by Human activity—ex. spilling of gasoline, combustion of FFs, natural sources (trees leaves in a forest and forest fire)

• Strong Aroma: chemicals within VOCS easily released into the air

If VOCS are Absent…

• nitrogen oxide accumulates in the atmosphere

• → later contributes to ozone destruction

If Large Presence of NOx + VOCs…

They combine and nitrogen oxide is no longer available to breakdown ozone by recombining with it

• → Result = large quantity of ozone accumulates

  • → presence of VOCs = ozone accumulation

Solution to Reducing Ozone and Photochemical Smog

• Must reduce nitrogen oxide and VOCs

4 Factors that Increase Smog Formation

1. More sunlight (summer, afternoon) = more O3

2. Warmer temperature, speeds evap. of VOCs and rxn that lead to O3

3. Higher VOCs emissions (gas stations, laundromats, petrochem. & plastic factories)

4. Increased vehicle traffic; increases NO2 emissions & therefore O3 formation

Why Do Urban Have More Smog?

• More traffic → more NO2

• Hotter temps due to low albedo of blacktop

• More VOCs due to gas stations & factories

• More electricity demand; more NOx emissions from nearby power plants

Smog Health Risks

• Burning and itching of eyes

• Irritate the nose and throat

• Coughing and a scratchy, sore throat

• Hard to breathe

• Inflame the air passageways and lungs = more susceptible to infection

O3 Formation

1. Day: Sunlight breaks NO2 → NO + O

2. O + O2 = O3

3. Night: O3 + NO = NO2 + O2 → O3 Levels drop

4. Afternoon: O3 Peaks

   1. Sunlight = most direct + NO2 from traffic peaks

5. Morning Commutes: High NO2 from car exhaust

Photochemical Smog Formation

1. Day: Sunlight breaks NO2 → NO + O

2. O + O2 = O3

3. w/o NO: O3 builds up = Photochemical Smog

ALTERNATIVELY:

1. VOCS + NO = Photochemical oxidants

2. O3 + PCO = Photochemical Smog