Title IV has been successful in reducing emissions of SO2 and NOx from power generation to the levels set by Congress. In fact, by 2009, SO2 emissions from power plants were already 3.25 million tons lower than the final 2010 cap level of 8.95 million tons, and NOx emissions were 6.1 million tons less than the projected level in 2000 without the ARP, or more than triple the Title IV NOx emission-reduction objective. As a result of these emission reductions, air quality has improved, providing significant human health benefits, and acid deposition has decreased to the extent that some acid-sensitive areas are beginning to show signs of recovery. Current emission reductions and the passage of time, which is needed for affected ecosystems to respond to the new environmental conditions, are expected to allow more acid-sensitive areas to recover. However, current emission-reduction levels (rules finalized as of spring 2005) are not sufficient to allow full recovery of acid-sensitive ecosystems. Estimates from modeling presented in this report show that additional emission reductions are necessary in order to protect acid-sensitive ecosystems.
This report analyzes a range of SO2 and NOx emission-reduction scenarios to evaluate the extent to which further reductions could achieve additional environmental recovery and minimize the adverse ecological effects associated with acid rain. The results of the modeling presented in this report indicate that broader recovery is not predicted without additional emission reductions. To fully protect acid-sensitive ecosystems in all regions affected by acid deposition will require reductions in acid-yielding emissions from source categories beyond power plant SO2 emissions. The information presented in this report provides part of what is needed to determine appropriate future action; other information that is needed includes the costs and other impacts of emission reductions, the role of climate change and multiple pollutant interaction, and the value the public places on further improvements to the environment and human health.
Burns, D.A., Lynch, J.A., Cosby, B.J., Fenn, M.E., Baron, J.S., US EPA Clean Air Markets Div., 2011, National Acid Precipitation Assessment Program Report to Congress 2011: An Integrated Assessment, National Science and Technology Council, Washington, DC, 114 p.