How do seasonal changes affect air composition?

Seasonal changes can affect air composition by altering the levels of certain gases, particularly carbon dioxide and ozone.

During different seasons, the concentration of certain gases in the atmosphere can vary. One of the most significant changes is seen in the levels of carbon dioxide (CO2). In the spring and summer, plants absorb CO2 for photosynthesis, which reduces the amount of this gas in the atmosphere. Conversely, in the autumn and winter, many plants decay and release CO2 back into the atmosphere, increasing its concentration.

Another gas affected by seasonal changes is ozone (O3). The concentration of ozone in the lower atmosphere, or troposphere, can increase during the summer months. This is due to the fact that sunlight and high temperatures accelerate the reactions that produce ozone from nitrogen oxides (NOx) and volatile organic compounds (VOCs). These reactions are slower in the cooler winter months, leading to lower ozone levels.

Seasonal changes also influence the amount of water vapour in the air. Warmer temperatures in the summer increase the rate of evaporation, leading to higher humidity levels. In contrast, cooler winter temperatures reduce evaporation rates, resulting in drier air.

Lastly, seasonal changes can affect the concentration of particulate matter in the air. For instance, during the winter, the burning of fossil fuels for heating can increase the levels of particulate matter in the atmosphere. Similarly, in some regions, agricultural practices such as burning crop residues can lead to increased particulate matter in the air during certain seasons.

In conclusion, seasonal changes can significantly affect the composition of the air by altering the levels of gases like carbon dioxide and ozone, as well as affecting humidity and particulate matter levels.