Why is weather important to air quality?

Meteorological conditions (weather) play an important part in determining the distribution and concentration of air pollutants.

• Wind speed - On a windy day air pollution is often very low; however, wind could also mean air pollutants get spread to location far away from the sources. Emission from continental Europe reaching the UK when there are strong wind whereas when there is low wind the dispersal of traffic emissions in cities can be poor leading to build up of pollutants.
• Wind direction - If the wind is blowing from an industrial area towards a city, the city’s air quality is likely to be poor.
• Air pressure - When air pressure is high, the air is usually still which allows air pollution to build up. When air pressure is low, the weather is often wet and windy, causing pollutants to be dispersed and 'washed out' of the atmosphere by rain.
• Rain - Rain can clean the air effectively washing out pollutants however while this is good for air quality, chemicals and compounds that pollute the air can be washed into soil and surface waters, this was the cause of acid rain that used to be a major environmental issue. As sulphur dioxide emissions have reduced this has become less of an issue.
• Sun - When the sun is more intense chemical reactions can take place in the atmosphere leading to increased pollution. This is the reason for higher ground level ozone on hot sunny days.