Frank Ripa, age 9, of Rome, New York, for his question:

What makes London so foggy?

London is famous for its pea soup fogs, so thick that noon becomes darker than midnight. Fogs are really clouds sitting on the ground and clouds ?re made from moisture in the air.

The air that blows over England has been warmed by the Gulf Stream coming up from the tropics. It is loaded with its quota of moisture evaporated from the sea. It is warm moist marine air.

In winter, the land becomes cooler than the sea. Warm moist ocean air clashes with cooler sir from over the land. The result is cloudiness, often so low that the clouds become fog. The fogs of London are made worse by city soot and smoke. So a London pea souper is really a very bad case of what in America we call smog.