Editing Emissions trading (section)

====Sulfur dioxide====
{{main|Acid Rain Program}}
An early example of an emission trading system has been the [[sulfur dioxide]] (SO<sub>2</sub>) trading system under the framework of the [[Acid Rain Program]] of the 1990 [[Clean Air Act (1990)|Clean Air Act]] in the U.S. Under the program, which is essentially a cap-and-trade emissions trading system, SO<sub>2</sub> emissions were reduced by 50% from 1980 levels by 2007.<ref>{{cite web
|url=http://www.epa.gov/airmarkt/progress/arp07.html
|title=Acid Rain Program 2007 Progress Report
|work=Clean Air Markets - Air & Radiation
|publisher=US EPA
|date=January 2009
|access-date=2011-07-25
|archive-date=2011-05-01
|archive-url=https://web.archive.org/web/20110501114253/http://www.epa.gov/airmarkt/progress/arp07.html
|url-status=live
}}</ref> Some experts argue that the cap-and-trade system of SO<sub>2</sub> emissions reduction has reduced the cost of controlling acid rain by as much as 80% versus source-by-source reduction.<ref name="stavins98"/><ref>{{cite journal | last1 = Carlson | first1 = Curtis | last2 = Burtraw | first2 = Dallas | last3 = Cropper | first3 = Maureen | last4 = Palmer | first4 = Karen L. | year = 2000 | title = Sulfur dioxide control by electric utilities: What are the gains from trade? | url = http://ageconsearch.umn.edu/record/10790/files/dp980044.pdf| journal = Journal of Political Economy | volume = 108 | issue = 6| pages = 1292–1326 | doi=10.1086/317681| s2cid = 3037737 }}</ref> The SO<sub>2</sub> program was challenged in 2004, which set in motion a series of events that led to the 2011 [[Cross-State Air Pollution Rule]] (CSAPR).  Under the CSAPR, the national SO<sub>2</sub> trading program was replaced by four separate trading groups for SO<sub>2</sub> and NO<sub>x</sub>.<ref>{{cite web
 |url         = http://www.epa.gov/crossstaterule/
 |title       = Cross-State Air Pollution Rule (CSAPR)
 |date        = 2011-07-09
 |access-date  = 2011-07-10
 |publisher   = United States Environment Protection Agency
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110711010737/http://www.epa.gov/crossstaterule/
 |archive-date = 2011-07-11
}}</ref>
SO<sub>2</sub> emissions from Acid Rain Program sources have fallen from 17.3 million tons in 1980 to about 7.6 million tons in 2008, a decrease in emissions of 56 percent.  A 2014 EPA analysis estimated that implementation of the Acid Rain Program avoided between 20,000 and 50,000 incidences of premature mortality annually due to reductions of ambient PM2.5 concentrations, and between 430 and 2,000 incidences annually due to reductions of ground-level ozone.<ref name="ex" />{{failed verification|date=June 2017}}