Monthly nitrogen dioxide concentrations in select cities in the UK 2020-2023
Concentrations of nitrogen dioxide (NO₂) in UK cities typically follow a similar pattern each year, with the highest levels normally observed in the winter months and the lowest in the summer months. An exception to this was in 2020, when several cities saw levels drop to lows in the spring, following the UK's first national COVID-19-related lockdowns and travel restrictions. NO₂ is mainly emitted by road transportation.