NOx and SO2

Emission Reductions:

NOx, SO2 and PM

Since 1990, our emissions of sulfur dioxide and nitrogen oxides are down over 80 percent, while electricity generation has increased about 30 percent to serve growing demand. Performance »

Through 2015, the Southern Company system:

  • Invested about $9.4 billion in environmental controls. We are planning to spend at least an additional $2.1 billion through 2018.
  • Developed, with U.S. Department of Energy and KBR, the TRIGTM advanced coal gasification technology. This technology turns coal into gas that can be used to generate electricity more cleanly than traditional coal-fired power plants.
  • Advanced one-of-a-kind, clean coal power generation, in partnership with the U.S. Department of Energy at the National Carbon Capture Center in Wilsonville, Ala.

Particulate Matter and Air Quality Research

Southern Company participates in data collection and research studies aimed at characterizing air quality, its sources, and health effects. Two leading studies, SEARCH and ARIES, have provided a foundation for air quality policy, practices and emerging issues.

SEARCH comprehensively measures air quality in the Southeast, including the myriad compounds comprising particulate matter and is used in a variety of air quality research and regulatory analyses, including studies on health effects. SEARCH hosted the summer of 2013, $20 million Southeast Atmosphere Study sponsored by NSF, NOAA, EPA, EPRI, and others focused on understanding the interactions of natural and man-made emissions in forming particulate organic matter. ARIES investigates associations between specific air pollution components and human health.



At the end of 2015, the Southern Company system was operating scrubbers at 28 coal units and selective catalytic reduction systems at 20 coal units. As of mid-year 2016, baghouses are operating at eight units.

Scrubbers – Sulfur Dioxide Removal

Emissions from burning coal contain sulfur dioxide. The scrubber sprays the combustion emissions with a water and limestone mixture. The sulfur dioxide reacts with the limestone to form gypsum, a reusable compound. The clean gas rises out of the stack. This system removes up to 95 percent of the sulfur dioxide.

SCRs (Selective Catalytic Reduction Systems) – Nitrogen Oxide Removal

Selective catalytic reduction (SCR) systems remove up to 85 percent of nitrogen oxides, another emission from burning coal. An SCR, or selective catalytic reduction system, adds ammonia to the gases exiting the boiler. A catalyzed chemical reaction breaks the nitrogen oxides down to harmless nitrogen and water. Catalytic converters in autos are similar devices.

Baghouses – Particulate Removal

Baghouses collect fly ash and other particulate matter. Baghouses work like vacuum cleaners, forcing the flue gas through filter bags, which collect more than 99 percent of the dust particles.

Devices like SCRs, scrubbers and baghouses require energy to operate. Typically, emission-control devices reduce generation by about 2.5 percent.