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Acid Rain Cycle
Source: Acid Rain Revisited, advances in scientific understanding since the passage of the 1970 and 1990 Clear Air Act amendments. Hubbard Brook Research Foundation. Science LinksTM Publication, Vol. 1, no. 1.
Effects of Acid RainHarmful to fish
Reduces tree health
Alters soil
• Increase mercury concentration• Increase inorganic aluminum exposure• Fatal in high concentrations
• Red spruce & sugar maple• Growth decline
• Winter injury
• Leaches base cations (e.g. calcium)• Mobilizes inorganic aluminum• Sulfur and nitrogen accumulation
…But now for some good news!• Clean Air Act (1970)
– Amended 1977 & 19901. Sets standards for SO2 & other pollutants and requires
implementation plans to ensure standards are met2. Directs EPA and States to establish air quality programs
which set enforceable emissions limits on large pollutant-emitting facilities
3. Authorizes EPA to set emission standards for motor vehicles and fuels
4. Set forth provisions to reduce acid rain• CAIR/CSAPR (2005)
– Cap and trade to reduce power plant SO2 and NOxemissions
• NH Air Toxics Control Program (1987)– Regulate hazardous air pollutant emissions
In 2011, a scrubber aimed to reduce mercury emissions when online at
PSNH (Eversource) Merrimack Power Station
It is also effective at reducing SO2
emissions
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
Thou
sand
Tons
Trend in US Sulfur Dioxide Emissions
0
10
20
30
40
50
60
70
80
1999 2002 2008 2011
Thou
sand
Tons
Sulfur Dioxide Emissions in New Hampshire
NHDES Acid Rain Monitoring ProgramsRooftop RainInitiated in 1972
pH, Sulfate, NitrateRemote Pond
Initiated in 1981Samples collected spring with NH Fish & GamepH, ANC, Specific conductance, Sulfate, Nitrate
Acid OutletInitiated in 1983
Samples collected spring & fall (associated with turnover)
pH, ANC, Specific conductance, Sulfate, Nitrate
NHDES Acid Rain Monitoring Programs
Individual parameters of individual waterbodies
Non-parametric Mann-Kendall trend tests
Significance declared a p ≤ 0.05
Nitrate: Detection limit 0.05 mg/L. Non detectable results assigned values of 0.025 mg/L to conduct
trend analysis
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
pH (U
nits
)pH Trends in Rooftop Rain at DES
Average pH Median pHSignificant increase
0
2
4
6
8
10
12
14
mg/
LSulfate Concentration of Rooftop Rain at DES
Mean MedianSignificant decrease
0
0.5
1
1.5
2
2.5
ppm
Nitrate Concentration of Rooftop Rain at DES
Mean MedianSignificant decrease
Are these precipitation trends reflected by our state waterbodies?
-0.4
0
0.4
0.8
1.2
4
4.5
5
5.5
6
6.5
REMOTE PONDpH & ANC Example
pH Acid Neutralizing Capacity (ANC)
pH (units) ANC (mg/L)
No significant trend
0
0.02
0.04
0.06
0.08
0.1
0.12
0
1
2
3
4
5
6
7
REMOTE PONDSulfate & Nitrate Example
Sulfate (SO₄²¯) Nitrate(NO3-) Not detectable
NO3- (mg/L)SO₄²¯(mg/L)
Significant decrease
0
5
10
15
20
25
umho
/cm
REMOTE PONDSpecific Conductance Example
Specific Conductance
Significant decrease
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% o
f Wat
erbo
dies
Remote Pond Trend Direction
IncreasingTrend
Stable
DecreasingTrend
pH ANCSpecific
conductance Sulfate Nitrate
5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
7
7.2
ph (u
nits
)ACID OUTLETpH Example
Fall Sampling Spring Sampling
No significant trend
0
1
2
3
4
5
6
7
mg/
LACID OUTLETANC Example
Fall Sampling Spring Sampling
Significant increase
0
1
2
3
4
5
6
mg/
LACID OUTLET
Sulfate Example
Fall Sampling Spring Sampling
Significant decrease
0%
20%
40%
60%
80%
100%
% o
f Wat
erbo
dies
IncreasingTrend
Stable
DecreasingTrend
Fall Spring
Acid Outlet Trend Direction
SummaryRooftop rain
– pH increase– Sulfate & nitrate decrease
Remote pond– Majority of pH & ANC stable
– 100% decrease in sulfate & specific conductance– Majority decrease in nitrate
Acid outlet– Majority of pH & ANC increasing or stable
– Greater improvements in Fall– ≥80% decrease in sulfate & nitrate
– Specific conductance results scattered
Take home messages
• Recovery is occurring but incomplete
• Sulfate concentration in waterbodies has drastically decreased, following reductions in sulfur dioxide emissions
• Long term datasets valuable for trend monitoring
Thanks!
• Dave Neils• Walt Henderson• Scott Ashley• Dave Healy• Jeff Underhill
Questions?
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