NORILSK, Russia — A former Siberian gulag with a population of about 210,000, this decrepit city has some of the worst air quality in the world. It is surrounded by dead trees, as far as the eye can see, poisoned by acid rain.

But to Vladimir M. Stratyev, the eye-stinging haze is an unalloyed blessing, for Mr. Stratyev is, in effect, a miner of air pollution. For him the smog of Norilsk is a mother lode.

The smelters here produce one-fifth of all the world’s nickel, a key alloy of stainless steel, while emitting 1.9 million tons of sulfur dioxide a year, more than the entire country of France. They also spew out 10,800 tons of heavy metal particulates.

For 50 years, a fine, black dust of heavy metals has fallen on the city, mostly nickel but some copper and cobalt as well. In the spring thaw, this soot runs into ponds and streams, where it settles on the bottom into strata that have built up in places three to five feet thick.