In an effort to reduce the adverse effects of acid deposition on human health and the environment, Congress established the Acid Deposition Control Program, which was passed in 1990 as Title IV of the Clean Air Act Amendments (hereafter Title IV). Title IV requires reductions in annual emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx), the precursors of acid rain, from electric utilities. EPA hopes to facilitate the use of localized monitoring where available in conjunction with national networks and promote ecological assessment initiatives at the state and tribal nation levels in order to better understand which regions of the country show signs of improvement and if any are continuing to degrade. This combination of local, regional and national ecosystem assessments will improve the decision-making and evaluation process regarding current air pollution control strategies. Phase I of the Acid Rain Program achieved substantial emission reductions, resulting in significant environmental and health benefits. As even greater emission reductions occur under Phase II of the Acid Rain Program (2000 forward), the ability to describe the ecological response to these reductions becomes increasingly important.

"June 2001." "EPA 430-R-01-005." Description based on printed copy of PDF document.