Why do cooler temperatures exacerbate smog conditions?

Cooler temperatures exacerbate smog conditions because they cause pollutants to stay closer to the ground, increasing their concentration.

Smog, a type of air pollution, is a mixture of smoke and fog. It is primarily composed of various pollutants such as nitrogen oxides, sulphur dioxide, ozone, smoke or particulates. These pollutants are usually emitted by industries, vehicles, and other sources of combustion. The concentration of these pollutants in the air is what determines the severity of the smog.

During cooler temperatures, especially in the winter months, the phenomenon known as temperature inversion occurs. Normally, air temperature decreases with an increase in altitude. However, during a temperature inversion, this normal temperature gradient is inverted, meaning the air is cooler near the ground and warmer above. This creates a sort of 'lid' that traps these pollutants close to the ground, preventing them from dispersing into the upper atmosphere. As a result, the concentration of pollutants in the air we breathe increases, exacerbating the smog conditions.

Furthermore, cooler temperatures can also lead to increased emissions of certain pollutants. For instance, in colder weather, people tend to use more energy for heating, leading to increased combustion of fossil fuels. This results in higher emissions of pollutants such as sulphur dioxide and particulates, which contribute to smog.

In addition, certain chemical reactions that result in the formation of smog, specifically photochemical smog, are facilitated by sunlight. Even though cooler temperatures might suggest less sunlight, it's the presence of sunlight, not necessarily heat, that drives these reactions. Therefore, even in cooler temperatures, as long as there is sunlight, photochemical smog can form.

In conclusion, cooler temperatures exacerbate smog conditions by causing pollutants to be trapped closer to the ground and by potentially increasing pollutant emissions. This is why smog is often a significant problem in urban areas during the winter months.