The strength of rubber is improved by adding this element in vulcanization.
Paul Crutzen has suggested injecting this element into the stratosphere to combat climate change. This element, which is one of the oldest known fungicides, comes in a wettable powder that can be used against powdery mildews. In a three tube process, superheated water is used to melt underground deposits of this element and then compressed air is used to force it up to the surface in the Frasch process. This element is uniquely found in the amino acids methionine and cysteine, the latter of which has a thiol side group. The strength of rubber is improved by adding this element in vulcanization. For 10 points, name this element that smells like rotten eggs. 
Paul Crutzen has suggested injecting this element into the stratosphere to combat climate change.
sulfur [or S] 