Lead is more familiar to us as a metal - think of old lead pipes in the plumbing of old buildings, or even on the rooves of very old buildings - it is even known as a 'heavy metal ', so it sounds unbelievable to think of it helping to make clouds...

but of course, the lead which helps to nucleate ice crystals at warmer temperatures and with less water than normal is not in the form of metal - it is released in the particles from burning fuel, particularly coal .

Action:

Some simple questions about clouds that you always wanted to know the answers to - with pics and activities here

and the NASA site here tells you about Cloudsat - to watch clouds from space!