Pollutant episodes are periods when pollutants reach unusually high concentrations for several days. They are usually driven by weather conditions.
Winter smogs are formed when a thin layer of the atmosphere near the earth becomes cooler than that above it. This is known as temperature inversion. When this happens pollutants are trapped at ground level until there is a change in weather conditions.
In the past winter smogs, known as ‘pea-soupers’, were common occurrences in Bradford caused by the burning of huge quantities of domestic and industrial coal in the valley bottom. Following the Clean Air Acts of 1956 and 1968 the amount of coal burnt in the city was significantly reduced and the occurrence and frequency of winter smogs decreased.
Modern winter pollution episodes are now caused mainly by traffic pollution. Although they are less frequent and less visible they are still of concern.
Summer smogs occur during hot sunny weather when nitrogen dioxide (mainly from road traffic) reacts with hydrocarbons in sunlight to form another pollutant called ozone. Particle levels also reach high concentrations during summer smog conditions. Ozone is a respiratory irritant and can make breathing difficult for people with asthma. During very bad summer smog episodes, even a normally fit and healthy person can experience irritation of the nose and throat, coughing and breathlessness.
Air pollution modelling is the use of mathematical theories and computer programmes to understand and predict the way pollutants behave in the atmosphere.
Modelling can be used to:
Air pollution models require lots of information about pollutant sources such as traffic flows, traffic compositions (type and age of fleet) and local combustion source data. This type of information is collected together in an emission database.
Complex dispersion models also need to receive information about local weather conditions, building heights and topography of the land.
The council has undertaken modelling of NO2 concentrations in and around the Bradford CAZ area. If you live in this area you can use the modelling to find out about air quality near you.
We hope to be able to expand the area of this modelling to cover a wider part of the district in the near future.
