Which of the following is NOT considered a main greenhouse gas?

Ozone (O3) is considered more of a secondary greenhouse gas compared to carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which are classified as primary greenhouse gases. Primary greenhouse gases are those that have a direct and significant impact on the greenhouse effect and are emitted directly from various sources, contributing to global warming.

While ozone does have greenhouse properties, it is less significant in terms of its direct contributions to climate change when compared to CO2, CH4, and N2O. These primary gases are produced through various human activities such as fossil fuel combustion, agriculture, and waste management, playing a crucial role in trapping heat in the atmosphere.

In contrast, ozone is primarily produced through chemical reactions between sunlight and pollutants like volatile organic compounds (VOCs) and nitrogen oxides (NOx). Consequently, its role is more complex and predominantly related to air quality issues rather than being a direct emissions-related greenhouse gas in the context of climate change discussions. This is why ozone is not typically classified as one of the main greenhouse gases.