At a typical urban site, the ground level ozone concentration would be maximum at what time of the day?

Correct option is B

Ground-level ozone (O₃) is a secondary pollutant formed by photochemical reactions between nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in the presence of sunlight. The concentration of ozone depends heavily on the intensity of solar radiation, which peaks during the afternoon. Hence, ground-level ozone concentrations are highest during the afternoon hours in typical urban environments.
Information Booster: · Mechanism of Ozone Formation:
· Sunlight drives the reaction between NOₓ and VOCs to produce ozone. The process begins in the morning when traffic emissions provide precursors (NOₓ and VOCs).
· The peak ozone levels occur in the afternoon due to maximum sunlight and atmospheric conditions conducive to photochemical reactions.
· Diurnal Variation in Ozone Levels:
· Morning: Ozone levels are low as NO from vehicle emissions reacts with existing ozone, reducing its concentration.
· Afternoon: Solar radiation is strongest, driving the photochemical reactions that form ozone.
· Evening and Night: Ozone concentrations decline as sunlight diminishes and NO reacts with ozone to form NO₂, depleting ozone levels.
· Factors Influencing Ozone Concentrations:
· Intensity of sunlight.
· Temperature (higher temperatures enhance ozone formation).
· Urban emissions from vehicles and industries.
Additional Knowledge: · Option (a) Morning:
· Ozone concentrations are typically low in the morning due to the absence of sunlight-driven reactions and the presence of nitrogen oxides that reduce ozone levels.
· Option (c) Evening:
· Ozone concentrations decrease in the evening as sunlight wanes and chemical reactions consuming ozone dominate.
· Option (d) Night:
· At night, ozone formation ceases due to the absence of sunlight, and its concentration further reduces through deposition and reactions with other pollutants, such as nitrogen oxides.