APES 7

Photochemical Smog

A type of air pollution formed when sunlight reacts with pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs).

Precursors of Photochemical Smog

Nitrogen dioxide (NO2), volatile organic compounds (VOCs), and ozone (O3) that contribute to smog formation.

Role of NO2 in O3 Formation

NO2 breaks down in sunlight, releasing oxygen atoms that bond with O2 to create ozone (O3).

Conditions for Smog Formation

Requires sunlight and warmth to facilitate the reactions that produce O3 and evaporate VOCs.

Sources of VOCs

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

O3 Formation Process

Sunlight splits NO2 into NO and oxygen atoms; the oxygen atoms then combine with O2 to form O3.

O3 Level Drop at Night

Ozone levels decrease as O3 reacts with NO to form NO2 and O2, reversing the formation process.

Peak O3 Formation Time

Occurs in the afternoon when sunlight is most intense and NO2 emissions from morning traffic peak.

Why Urban Areas have More Smog

Higher traffic, increased temperatures from blacktop surfaces, more VOCs from gas stations and factories, and more NOx emissions from power plants.

Environmental Impacts of Smog

Reduces sunlight for photosynthesis; O3 can damage plant stomata and irritate animal respiratory tracts.

Human Health Impacts of Smog

Includes respiratory irritation, exacerbation of asthma, bronchitis, COPD, and eye irritation.

Economic Impacts of Smog

Results in lost productivity from sick workers and decreased agricultural yields due to limited sunlight and plant damage.