Nitrogen dioxide (NO₂) is a reddish-brown gas with a characteristic sharp, acrid smell. It is a significant air pollutant, primarily produced from burning fossil fuels, such as in vehicles and power plants. NO₂ can contribute to the formation of ground-level ozone and fine particulate matter, which can harm human health and the environment. Exposure to nitrogen dioxide can lead to respiratory issues, especially in vulnerable populations like children and those with pre-existing lung conditions. It can irritate the airways and decrease lung function. Reducing NO₂ emissions is essential for improving air quality and protecting public health.