Which substance is not considered to be an air pollutant?

Nitrogen gas (N2) is not considered an air pollutant because it makes up about 78% of the Earth's atmosphere and is a naturally occurring component. It is inert under standard atmospheric conditions and does not contribute to air pollution or have any adverse effects on human health or the environment. In contrast, substances like sulfur dioxide (SO2), carbon monoxide (CO), and particulate matter are pollutants that can have harmful impacts on air quality and public health, causing various respiratory and environmental issues. Therefore, nitrogen gas stands out as a safe and essential element of the atmosphere, differentiating it from the harmful substances that are classified as air pollutants.