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Nitrogen Oxides

Nitrogen oxides (NOx) are pollutant gases produced by burning fossil fuels, motor-vehicle exhaust, decaying vegetation, and many industries. Although high levels of NOx are detrimental to human health, the main concern is their role in the production of ozone and acid rain.

Ozone is formed by a series of complex reactions involving other chemical substances, primarily NOx and volatile organic compounds. The most effective strategies in the Tennessee Valley for ozone reduction focus on the control of NOx emissions, since most volatile organic compounds in the region come from natural sources.

A large proportion of the Tennessee Valley’s NOx emissions are generated by human activity: automobiles, trucks, and other mobile sources produce about a third of the total NOx emissions, and fossil power plants produce 10 to 15 percent. NOx is also the second-largest human-generated source of excess acidity in rain, after sulfur dioxide.

NOx emissions at TVA plants


See raw data for this chart

Year Total
1974 395042
1975 370960
1976 434352
1977 410299
1978 394159
1979 375975
1980 393331
1981 377320
1982 304664
1983 310195
1984 302708
1985 356072
1986 384226
1987 369676
1988 391712
1989 365292
1990 404305
1991 405080
1992 464215
1993 508013
1994 469079
1995 534012
1996 495625
1997 511157
1998 414390
1999 357554
2000 286142
2001 270815
2002 263562
2003 236822
2004 199812
2005 191305
2006 198122
2007 196278
2008 168434
2009 58497
2010 72139
2011 63645
2012 54619
2013 46898

* Data includes 80 tons from units that produce less than 25 megawatts that are not required to reported to the Environmental Protection Agency.

What TVA is doing about NOx emissions

TVA has reduced its emissions of nitrogen oxides by about 90 percent since 1995. At present, 58 of TVA’s 59 coal-fired units have combustion controls to reduce NOx. The 59th is an atmospheric fluidized bed combustion plant, which, by design, already operates with low NOx emissions

TVA also operates year round selective catalytic reduction (SCR) systems on 21 of its largest coal-fired units and selective noncatalytic reduction (SNCR) systems on 8 smaller units. SNCR includes a variant know has Higher Energy Reagent Technology (HERT). All five of TVA’s natural gas fired Combine Cycle Plants  have SCRs to reduce nitrous oxide emissions.

TVA plans to continue a NOx emission reduction strategy that depends primarily on the installation of SCR systems. In August 2011, the TVA Board approved the installation of new SCRs at the Gallatin Fossil Plant by 2017.

TVA staff continue to look for better, more cost-effective ways to reduce emissions while continuing to supply reliable, affordable electricity and manage debt in the light of evolving emission reduction requirements. 

Emissions by plant



Bull Run






John Sevier




Lagoon Creek






Widows Creek

Other sites


Emissions by type

Carbon Dioxide

Nitrogen Oxides


Sulfur Dioxide

Greenhouse Gases

Toxics Release Inventory (TRI)

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