I’ve just arrived in Moscow for a meeting — the subject will be soot.

You may hear it called black carbon or even elemental carbon. Scientists getting technical will call it the “light-absorbing part of particles suspended in the atmosphere.” Let’s just keep it simple and call it soot.* (More on black carbon.)

It’s almost certainly the most visible air pollutant. You have seen it in the black smoke of old diesel engines or a smoldering campfire.

It’s by no means new. We’ve been fouling the air with it for as long as we’ve had fire. Once we began to burn stuff to extract energy, we brought this form of pollution into our midst. You can find the stuff coating the