APES 7

7.2: PHOTOCHEMICAL SMOG

Precursors of photochemical smog: NO2 as it contributes to the formation of O3, VOCs (hydrocarbons that bind with NO and form photochemical oxidants) as they volatilize (evaporate) easily, making them smelly, and O3 that is formed by NO2

Conditions needed for photochemical smog formation: sunlight as it drives the O3 formation, and warmth as it speeds the the O3 formation and the evaporation of VOCs

Sources of VOCs: gasoline, formaldehyde, cleaning fluids, oil-based paints, even coniferous trees (pine smell)

How O3 forms: sunlight breaks NO2 into NO and O, then O bonds with O2 to form O3

How O3 levels drop overnight: O3 reacts with NO to form NO2 and O2 once again, reversing the process

When does O3 formation peak: in afternoon when sunlight is most direct and NO2 emissions from morning traffic have peaked

How photochemical smog forms: O3 combines with photochemical oxidants (NO + VOCs)

Why do urban areas have more smog: more traffic (more O2), hotter temperatures due to lower albedo of blacktop, more VOCs due to gas stations and factories, more electricity demand; more NOx emissions from nearby power plants

Environmental impacts of smog: reduces sunlight, limiting photosynthesis, O3 damages plant stomata and irritates animal respiratory tracts

Human impact of smog: respiratory irritation, worsens asthma, bronchitis, COPD, irritates eyes

Economic impacts of smog: lost productivity due to sick workers missing work or dying, and decreased agricultural yields due to less sunlight reaching crops and damage to plant stomata

Ways to reduce smog: decreasing number of vehicles on the road and using carpooling, public transport, biking, walking, or working from home, and increased electricity production from renewable sources that don’t emit NOx