At what time of day is ozone least efficient?

Ozone is least efficient in the atmosphere during the noon hours. This is primarily due to the interaction of sunlight with atmospheric conditions. At noon, the sun's rays are at their strongest, resulting in increased photodissociation, which means that any ozone present is more likely to break down into other compounds rather than performing its protective functions.

Furthermore, ozone formation in the atmosphere is greatly influenced by sunlight and pollutants, particularly during the warmer parts of the day. While ozone can be more prevalent in the atmosphere during midday, its efficiency as a protective barrier or as a pollutant decreases due to higher temperatures and the intense solar radiation available at that time.

In contrast, ozone levels often increase during the morning and may have a more stable presence during the evening as temperatures decrease, and photochemical reactions slow down. At night, ozone is also less affected by direct sunlight, but it tends to dissipate due to lower temperatures and reduced emissions from nearby sources. Thus, noon is when ozone is least effective in performing its roles, making it the best choice for this question.