I'm not sure about the "layer of sulfur" part. The sulfur oxides are gasses, and they contribute to the formation of acid rain, so there's some in the atmosphere and some in the water. They occur naturally through things like volcanoes and forest fires, and I think they come out of the ocean, as well, so they've pretty much always been around.
In the U.S., we've cut back a lot on the man-made component through (gasp) environmental regulations, but before a war of flaming posts breaks out over regulation I'd like to note the following. Under the Clean Air Act (as amended) increasingly tight limitations were placed on sulfur emissions from burning coal (at power plants, etc.), but at least until now the limitations have been satisfied (through conversion to low-sulfur coals, scrubbers, etc.) while coal use has continued to grow. In this case, the regulations spurred a few changes and innovations that greatly reduced the damage from acid rain without hindering the overall use of coal.
Not sure how long it will take for China and other big developing coal users to figure that out...