How can urban heat island effects influence urban air pollutant concentrations?

• A. Higher temperatures boost ozone formation; increased energy use and stagnant air can elevate pollutant concentrations.
• B. Higher temperatures always reduce ozone.
• C. Urban heat islands decrease PM by increasing cleaning effects.
• D. They have no impact on air quality.

Answer: (A)

Urban heat islands raise city temperatures, which makes the photochemical production of ground-level ozone more efficient. Ozone forms when sunlight drives reactions between NOx and VOCs, and higher heat accelerates those reactions while also increasing VOC emissions from surfaces. At the same time, hotter days boost energy use for cooling, bringing more emissions from power plants and vehicles that supply those days’s electricity. The warmth is often paired with stagnant air and atmospheric stability in urban areas, which limits mixing and keeps pollutants from dispersing, so they accumulate rather than disperse. Put together, these factors mean higher temperatures in cities tend to increase ozone and overall pollutant concentrations, not reduce them.