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 transportation 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
2014 51281
2015 43682
2016 40706

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

What TVA is doing about NOx emissions

TVA has reduced its emissions of nitrogen oxides by about 91 percent since 1995.

TVA operates year-round selective catalytic reduction (SCR) systems on 21 of its largest coal-fired units and selective noncatalytic reduction (SNCR) systems on eight smaller units. SNCR includes a variant know as higher energy reagent technology (HERT). All of TVA’s natural gas-fired combined 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.