Nitrogen oxides (NOx), primarily nitric oxide (NO) and nitrogen dioxide (NO₂), are major air pollutants formed during high-temperature combustion processes in vehicles, power plants, industrial furnaces, and biomass burning. These reactive gases contribute significantly to environmental and health problems, making their control a critical issue in air quality management. NOx forms when nitrogen and oxygen in the air react under high heat. Thermal NOx is created at combustion temperatures above 1300°C, common in power stations and engines. Prompt NOx occurs in fuel-rich zones at lower temperatures when hydrocarbon radicals react with nitrogen. A third type, fuel NOx, originates from nitrogen compounds in fuels like coal or heavy oil. NOx contributes to multiple environmental problems. It plays a key role in the formation of ground-level ozone (smog), which harms respiratory health and plant life. NOx also reacts with other chemicals to create fine particulate matter (PM2.5), increasing the risk of cardiovascular and respiratory diseases. Additionally, NOx leads to acid rain, which damages soil, aquatic systems, and buildings, and causes eutrophication—overfertilization of water bodies resulting in oxygen-depleted dead zones. Although NOx indirectly affects climate by forming both warming tropospheric ozone and cooling aerosols, its net impact tends to promote warming. Health effects of NOx include lung irritation, asthma, COPD, and increased hospital visits, especially among children and the elderly. To mitigate NOx emissions, industries and transportation sectors employ technologies such as low-NOx burners, selective catalytic reduction (SCR), and engine modifications. Regulations like the Clean Air Act and EU emissions directives have reduced NOx levels in many developed countries. In summary, NOx pollution is a serious environmental and public health issue. Addressing it requires advanced technology, strict regulation, cleaner fuels, and public awareness to ensure cleaner air and a healthier ecosystem.