The US cap and trade on sulphur dioxide emissions was passed in 1990.
Overall, the Program's cap and trade program has been successful in achieving its goals. Since the 1990s, SO2 emissions have dropped 40%, and according to the Pacific Research Institute, acid rain levels have dropped 65% since 1976.[15][16] However, this was significantly less successful than conventional regulation in the European Union, which saw a decrease of over 70% in SO2 emissions during the same time period.[17]
S02 emissions were also falling from a peak in the late 1970s toward the 1990s, in other words the US S02 trading scheme was on an already declining path and was less successful than more direct European approaches.
S02 emissions trading was also local and not between countries which is another area where the proposed Green House Gas emissions trading schemes fall down. A corrupt county can just 'create' permits and then sell them. This has already happened with European and other schemes.
A tax would be a much more honest, much more transparent scheme than an Emissions Trading Scheme (ETS). ETS type solutions are attractive largely because politicians don't have to say they are a new tax, they can be easily gamed by giving out free permits and Enron style firms (including Enron itself before it went bankrupt) see a potential bonanza.