Map showing changes in annual average nitrogen dioxide concentration from 2000 to 2019. Purple areas on the map show places with a decrease in nitrogen dioxide concentration of 5 million parts per billion whilst red areas show areas with an increase in nitrogen concentration of 3 million parts per billion. Increases in nitrogen dioxide in cities has been linked to an increase in paediatric asthma. Data used to create this map was obtain using a land regression model and data collected from the Ozone Monitoring Instrument on the Aura satellite.