Final answer:
Nitrogen (N₂) is not considered a harmful pollutant under normal conditions, unlike other gaseous pollutants such as nitrogen oxides, carbon monoxide, sulfur oxides, and methane.
Step-by-step explanation:
The gaseous pollutant that is NOT considered significant is nitrogen (N₂). Nitrogen is a diatomic molecule that makes up about 78% of Earth's atmosphere and is not classified as a harmful pollutant under normal conditions. However, various compounds of nitrogen, such as nitrogen oxides (NOx), which include nitrogen dioxide (NO₂) and nitric oxide (NO), are significant pollutants contributing to smog and acid rain. These are emitted from combustion processes, like those found in vehicle engines and power plants. Carbon monoxide (CO), sulfur oxides (SOx), and methane (CH₄) also generate concern due to their harmful effects on human health, the environment, and their contribution to global warming. Carbon monoxide is a byproduct of incomplete combustion, sulfur oxides come from the burning of sulfur-containing fuels, and methane is a potent greenhouse gas primarily released during agricultural activities and the decay of organic waste.