Temperature inversion traps pollution at ground level

Pollution events are more likely to occur under temperature inversion conditions. During extended periods of high pressure in winter months, solar radiation reaches the ground, warming it up. At night, the lack of cloud cover means the ground loses heat rapidly and the air in contact with the ground becomes colder. The warmer air rises and acts as a lid trapping the colder air close to the ground. Pollution, including that from road traffic is also trapped, so the air layer closest to the ground becomes more and more polluted. This continues until the prevailing meteorological conditions change.