In 2006, annual sulfur dioxide, SO2, emissions from acid rain program electric power generation sources fell sharply. Sources emitted 9.4 million tons of SO2 last year, below the emission cap of 9.5 million tons.
Reductions amounted to 830,000 tons from 2005 levels and an overall reduction of 40 percent from 1990 levels, according to the EPA.
In the United States, the electric power industry accounts for 70 percent of total annual sulfur dioxide emissions.
In addition, emissions of nitrogen oxides, NOx, are down by over three million tons since 1990 and had decreased to nearly half the level anticipated without the Acid Rain Program.
Sulfur dioxide and nitrogen oxides are the key pollutants that form acid rain. Nitrogen oxides combine with volatile organic compounds to form smog and nitrates. These pollutants contribute to the formation of fine particles that are associated with human health effects and regional haze.
These pollutants, in their various forms, lead to the acidification of lakes and streams rendering some of them incapable of supporting aquatic life. They impair visibility innational parks, create respiratory and other health problems in people, weaken forests, and degrade monuments and buildings.
The reductions documented by the EPA have led to what the agency describes as 'a significant decrease in acid deposition, resulting in improved water quality in U.S. lakes and streams. 'Reduced formation of fine particles, improved air quality and human health related benefits are all results from the reduction of these emissions,' the agency said.
Since 1995, the market-based cap and trade program has reduced acid deposition in the United States by decreasing sulfur dioxide and nitrogen oxide emissions. The EPA says, 'The program's rigorous emissions monitoring and allowance tracking has resulted in nearly 100 percent compliance with the program.'
Environmentalists agree that the cap-and-trade program is working but say ecosystem monitoring is still needed.
William Cooke, director of government relations with Citizens Campaign for the Environment, says the EPA figures are showing the general trend accurately.
The group, based in Albany, New York with offices throughout New York and Connecticut, has been working on the acid rain issue for years.
'We are delighted with the changes,' said Cooke. 'SOX is down 40 percent, NOX is down 50 percent. We are headed in the right direction. The trading system is working real strong.'
'It's an awful lot better that it was in 1990s,' said Cooke. 'The first step was to stop making it worse, we did that. The second step was to start making it better - that's happening.'
'The third step is - how much better. Are we there yet? We don't know.'
Cooke says it is important to keep monitoring the ecosystem. Three or four research stations have scientific teams that measure the water quality day to day, month to month, but the Bush administration wants to cut funding to these researchers, a cut reflected in the budget now before Congress.
'Team Bush is taliking about cutting a few million dollars,' said Cooke. 'We can't understand that, we're seeing water quality changes, seeing forest health changes - why stop monitoring now?'
He explains that it takes trees a while to recover when you stop dumping acid rain on the Adirondacks, and it takes the soil an even longer time to recover.
The EPA points to the Clean Air Interstate Rule, promulgated in March 2005 to address transport of fine particles and smog in the eastern United States. This rule is supposed to further reduce SO2 and NOx emissions by about 70 percent and 60 percent respectively from 2003 levels.
A 2005 EPA study estimates that in 2010, the Acid Rain Program's annual benefits will be approximately $122 billion, at an annual cost of about $3 billion - a 40-to-1 benefit-to-cost ratio.
Still, environmentalists say the whole system relies on constant monitoring, and budget cuts to the monitoring program would be premature.
'At the end of the day,' Cooke said, 'it's about protectng the ecosystem, people's health, fish health. We need to continue to monitor.'