Photochemical Smog
Ground-level ozone pollution formed from nitrogen oxides and volatile organic compounds via photochemical reactions driven by sunlight.
Formula
NO2 + hν → NO + O; O + O2 → O3
Real World
Los Angeles regularly exceeds WHO ozone limits on hot, sunny, low-wind days; in August 2020 the city recorded its worst ozone episode in 30 years, directly linked to elevated VOC emissions from wildfires combining with urban NOx.
Exam Focus
State that photochemical smog is a secondary pollutant — examiners specifically credit distinguishing primary from secondary air pollutants.
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