Where air pollution levels are high, adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors.
People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion.
Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors.
This map shows current pollution levels across London. More information is available here.