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?