7.2: Photochemical Smog

What are the main precursors of photochemical smog?

NO2 (Nitrogen Dioxide), VOCs (Volatile Organic Compounds), and sunlight.

How does sunlight contribute to ozone (O3) formation?

Sunlight breaks down NO2 into NO and free O, which then binds with O2 to form O3.

What role do VOCs play in photochemical smog formation?

VOCs bind with NO to form photochemical oxidants, contributing to smog.

What is the effect of higher temperatures on ozone formation?

Higher temperatures speed up the evaporation of VOCs and the reactions that lead to O3 formation.

When do ozone levels typically peak?

Ozone levels typically peak in the afternoon when sunlight is most direct and NO2 emissions are high.

What happens to ozone levels at night?

At night, ozone reacts with NO to form NO2 and O2, causing O3 levels to drop.

What are the environmental impacts of photochemical smog?

It reduces sunlight, limiting photosynthesis, and damages plant stomata.

How does photochemical smog affect human health?

It acts as a respiratory irritant, worsening conditions like asthma, bronchitis, and COPD.

What are some strategies to reduce photochemical smog?

Reducing vehicle numbers, using public transport, and implementing catalytic converters.

What is the relationship between NO2 concentration and ozone concentration?

As NO2 concentration increases, ozone concentration also increases until it peaks in the afternoon.

What are common sources of VOCs?

Sources include gasoline, formaldehyde, cleaning fluids, oil-based paints, and emissions from coniferous trees.

What is the chemical reaction for ozone formation from NO2?

NO2 is broken down by sunlight into NO and O, where O then binds with O2 to form O3.

What are the economic impacts of photochemical smog?

Increased healthcare costs, lost productivity due to sick workers, and decreased agricultural yields.

How does increased vehicle traffic contribute to photochemical smog?

More vehicles lead to higher NO2 emissions, which increases ozone formation.

What is the significance of urban areas in relation to photochemical smog?

Urban areas typically have higher smog levels due to increased traffic, higher temperatures, and more VOC emissions.

What is the role of catalytic converters in reducing smog?

They convert CO, NOx, and hydrocarbons into less harmful substances like CO2, N2, O2, and H2O.

What are the peak times for NOx and VOCs concentrations?

NOx and VOCs peak early in the day, while ozone concentrations peak in the afternoon.

What happens to ozone when there is no NO to react with during the night?

Ozone builds up instead of converting back to O2 and NO2, leading to higher overnight concentrations.

What is the significance of the phrase 'photochemical oxidants'?

Photochemical oxidants are formed when VOCs bond with NO, contributing to the formation of smog.

What is the relationship between the time of day and ozone formation?

Ozone formation is influenced by sunlight, peaking in the afternoon when sunlight is strongest.