evidence: Air quality statistics in the UK, 1987 to 2023 - Nitrogen dioxide (NO2) [...] Nitrogen dioxide (NO2) is a gas that is mainly produced during the combustion of fossil fuels, along with nitric oxide (NO). NO2 can also be formed when NO reacts with certain gases in the atmosphere, such as ozone. These reactions take place very quickly and are reversible, so the two gases are referred to together as nitrogen oxides (NOx). [...] Urban background NO2 pollution has reduced both in the long-term and in recent years