Julian Warriger

There are large parts of it.

The trouble is that there's no scientific information either out of the capital.

So they've no idea what the air quality is at the moment.

But it is a very acute thing.

So what persists is going to be unknown.

There's one other thing which I did read, which is they use a particular form of oil in Iran, which is called mazout, which is rather thick and nasty.

It has very high levels of sulfur in it.

So that also, if that's been burned in these fires, that's going to be a particular reason why there's a problem.

BBC science reporter Roland Pease.