Impact of Federally-Mandated Emission Controls on Ambient Air SO₂ and NO_x Concentrations in Tampa, FL, USA

A landmark agreement between the USEPA and the State of Florida and the Tampa Electric Company (TEC) featured substantial reductions in SO₂, NOx, and PM emissions from two coal-fired power plants in Tampa, Hillsborough County, FL. The TEC committed to re-powering the FJ Gannon power plant from coal to natural gas, re-naming the plant to the Bayside power plant; to adding SO₂ scrubbers on two older boiler units at their Big Bend power plant; and to the installation of NOx controls on the Big Bend power plant. Between 1997 and 2005, an annual average decrease of 10 μg m^–3 in ambient air SO₂ concentrations at an urban monitoring site in Hillsborough County, Florida, accompanied the removal by TEC of 140,000 metric tons of SO₂ from the emissions inventory. Over this period, the observed change in annual average NOx concentrations at one urban monitor was 5 μg m^–3, which was reasonably consistent with the SO₂ reduction rate (e.g., 1 μg m^–3 for every 14,000 metric tons of SO₂ removed). Downward temporal trends at urban monitors unadjusted for seasonal dependencies, however, were statistically significant for SO₂ but not for NOx concentrations.