ثنائي أكسيد النيتروجين
Air pollution along the A400 varies. Air pollution is monitored by the City of Westminster, the London Borough of Camden, and the London Borough of Islington. Levels of Nitrogen dioxide (NO2) sometimes exceed the Air Quality Objective, set by the UK Department for Environment, Food, and Rural Affairs (Defra) at 40 micrograms per metres cubed (μg/m^3). Exposure to high levels of NO2 can lead to respiratory problems, and the gases sometimes inflame the lining of the lungs, reducing immunity to lung infections.