Acid Rain in New England

Trends

These figures show how SO2 and NOx emissions from power plants in New England in the Acid Rain Program have decreased since 1990. Data for 1995 and later years comes from continuous emissions monitor data as reported by EPA’s Clean Air Markets Division’s Acid Rain Progress Reports (EPA HQ) or Emissions Data and Compliance Reports. Data for 1990-1994 are estimates based on fuel usage and EPA’s conversion factors. It is provided by the Clean Air Markets Division.

Click here to see graphs for each individual state.

The graphs presented above show how emissions (i.e., what we put into the air) have changed over time. We next look at some observations of how deposition (i.e., what comes out of the air) has changed over time.

As emissions of sulfur dioxide have decreased, we have noticed some improvement in the atmosphere in recent years. A recent report prepared for EPA by Paul Miller of the Northeast States for Coordinated Air Use Management (NESCAUM) shows a decrease of about 25% in average sulfate deposition in Maine between 1980 and 1999. Similar decreases in sulfate deposition have been observed through much of the Northeast.

Data for 1993 through 1998 show no marked systematic trend of pollutants in precipitation for the New England sites. Sulfate deposition in 1995 showed a marked decline at every monitoring site in New England, except the Acadia NP site in Maine. The average 1995 sulfate deposition in New England was the lowest ever recorded during the 20 years of sulfate deposition monitoring. The 1996 data indicate that sulfate deposition increased in eight of the ten sites. Nonetheless, sulfate levels in 1996 were about 16% below historical averages (1979-1995). The 1996 data show similar increases occur for nitrate at most sites, and these increases appear to be further enhanced in 1997. In 1998, however, nitrate deposition decreased at each of the ten trend sites. Nitrate deposition during 1998 remained virtually the same as the historical average (1979-1998). In the years since 1998, the we have seen a trend toward less sulfate in precipitation in New England. Until about 2000, trends in nitrate remained fairly constant, but since 2000, even the nitrate deposition in New England has begun to decrease.

The year to year variation that is recorded at the NADP sites can be attributed to differences in precipitation and prevailing wind patterns, as well as emission sources. This is characteristic of precipitation data and should be viewed as normal. Trends in pollutant deposition within New England, whether due to long-term changes in pollutants emitted to the atmosphere, or trends in climate, will be evident only after many years (10-20+ years).

Lakes and streams have been slower to respond, but we have begun to see improvement. A report in "Nature" Magazine in 1998 showed some improvement in lakes in Maine, but not elsewhere in New England. In 2003, EPA compiled an assessment of the surface chemistry of lakes and streams in the northern and eastern United States. This assessment showed that the concentration of sulfate in New England lakes is decreasing. About 30% of the lakes in New England that were acidic are no longer considered acidic. In New England, the "Acid Neutralization Capacity" (ANC), the ability of the environment to neutralize acidic precipitation has not significantly improved, but this was observed in the Adirondacks and in other areas. The soil in New England is slower to react than that in the Adirondacks, so it will take longer for the ANC in New England to improve.

The full recovery of New England's aquatic ecosystems will take more time. In some cases, it will be decades before we see ecosystems fully restored to their pre-industrial condition.