-NO2, or nitrogen dioxide, 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. Nitrogen dioxide is part of a group of gases known as nitrogen oxides (NOx), which can contribute to the formation of smog and acid rain, impacting both human health and the environment. Exposure to high levels of nitrogen dioxide can lead to respiratory problems and aggravate conditions like asthma. It can also harm ecosystems by affecting soil and water quality. Monitoring and regulating NO2 levels is essential for maintaining air quality and protecting public health.