Dry deposition is difficult to measure directly. There have been attempts to use a
method similar to that for wet deposition, but it usually takes too long to cover the
collector when rain starts. It takes only a few drops of rain to contaminate a dry
deposition sample. The Clean Air Status and Trends Network (CASTNet) calculates
dry deposition using atmospheric conditions, meteorological data, and information
on land use, vegetation, and surface conditions.
Other programs have looked at changes in the acidity of lakes, streams, and soil.
Monitored data for some lakes are available from as early as 1980. Facilities such as
Hubbard Brook in New Hampshire have been measuring the acidity of streams and
lakes on their 7800-acre property. They also have looked at soil chemistry and
effects on the entire ecosystem.
In addition to specific efforts to measure acid rain, EPA maintains monitoring
networks for monitoring SO 2 and NO 2 in the air for other programs. Although these
programs are not intended to consider acid rain, they do give us an idea of the
amount of these chemicals in the air at certain locations.
8.9 Trends
Figures 7.16 and 7.17 show how SO 2 and NO x emissions from power plants in New
England in the Acid Rain Program have decreased since 1990 to 2011. Data for 1995
and later years come from continuous emissions monitor data as reported by US
EPA’s Clean Air Markets (CAM) Division’s Acid Rain Progress Reports 2013 or
Emissions Data and Compliance Reports [70].
Data for 1990–1994 are estimates based on fuel usage and US EPA’s conversion
factors. It is provided by the Clean Air Markets Division.
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
7 Lake Restoration
295
method similar to that for wet deposition, but it usually takes too long to cover the
collector when rain starts. It takes only a few drops of rain to contaminate a dry
deposition sample. The Clean Air Status and Trends Network (CASTNet) calculates
dry deposition using atmospheric conditions, meteorological data, and information
on land use, vegetation, and surface conditions.
Other programs have looked at changes in the acidity of lakes, streams, and soil.
Monitored data for some lakes are available from as early as 1980. Facilities such as
Hubbard Brook in New Hampshire have been measuring the acidity of streams and
lakes on their 7800-acre property. They also have looked at soil chemistry and
effects on the entire ecosystem.
In addition to specific efforts to measure acid rain, EPA maintains monitoring
networks for monitoring SO 2 and NO 2 in the air for other programs. Although these
programs are not intended to consider acid rain, they do give us an idea of the
amount of these chemicals in the air at certain locations.
8.9 Trends
Figures 7.16 and 7.17 show how SO 2 and NO x emissions from power plants in New
England in the Acid Rain Program have decreased since 1990 to 2011. Data for 1995
and later years come from continuous emissions monitor data as reported by US
EPA’s Clean Air Markets (CAM) Division’s Acid Rain Progress Reports 2013 or
Emissions Data and Compliance Reports [70].
Data for 1990–1994 are estimates based on fuel usage and US EPA’s conversion
factors. It is provided by the Clean Air Markets Division.
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
7 Lake Restoration
295