Nitrogen oxides (NOx) are a group of gases that are produced by the burning of fossil fuels. They are a major contributor to air pollution and can cause a variety of health problems, including:

* Respiratory problems: Nitrogen oxides can irritate the airways, causing coughing, wheezing, and shortness of breath. They can also contribute to the development of asthma and other chronic respiratory diseases.

* Cardiovascular problems: Nitrogen oxides can damage the blood vessels, leading to an increased risk of heart attacks, strokes, and high blood pressure.

* Cancer: Nitrogen oxides have been linked to an increased risk of lung cancer and other types of cancer.

* Environmental problems: Nitrogen oxides can contribute to the formation of smog and acid rain. They can also damage plants and animals.

Nitrogen oxides are a serious environmental and public health problem. Reducing emissions of NOx is essential for improving air quality and protecting human health.