Is the weather different at weekends? It may seem a strange question, but a study of rainfall in Rochdale, Lancashire, in the 1920s revealed that weekdays often were wetter than weekends.

The reason was clear to see – during the week factories belched out coal smoke. That filled the atmosphere with particles of smut, which acted as seeds for droplets of water to form on to, and eventually grew into raindrops. At the weekends there was less smoke and so there was less rain.

These days the coal smoke has gone, but has the weekly weather cycle disappeared? A recent study found a surprisingly similar pattern of rainfall in the southeastern United States, where the middle of the week was wettest, and Sundays were the driest day of the week. This rainfall pattern has become increasingly evident only since the 1980s.

Quite what lies behind this is not clear, although it could be something to do with the growth of road traffic pollution, especially diesel engine fumes. These give off tiny particles and, like the smut from coal smoke, could help to seed water droplets in the air that grow into raindrops.

Another study in the southeast US also revealed that summer thunderstorms are most common and intense on Wednesdays and least common at weekends. Again, this mirrored diesel traffic pollution. So perhaps weekend weather is not so bad after all.