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Acid Rain

Small image of the forming of acid deposition
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Acid rain comes in many forms: rain, snow, sleet, hail, and fog (wet deposition), and as acid particles, aerosols, and gases (dry deposition). Acid deposition forms when sulfur dioxide (SO2) and nitrogen oxides (NOx) combine with moisture in the atmosphere to produce sulfuric acid and nitric acid.

By the 1960s, it became clear to scientists that acid deposition was devastating natural resources across New York. The Catskill and Adirondack Mountains were particularly hard hit. Soils were becoming too acidic to maintain healthy forests with noticeable tree die-offs at higher elevations. Many lakes, mountain streams, and some rivers were unable to support healthy populations of fish.

Causes of Acid Rain

Several sources that contribute to creating acid rain include:

  • Combustion of fossil fuels (coal, oil, natural gas, wood, etc.) for energy.
    • SO2 emissions have been reduced in modern power plants with the introduction of low-sulfur fuel and the use of scrubbers in the smokestacks to remove the sulfur from the emissions. According to the U.S. Energy Information Administration, the US consumption of coal for electric generation has dropped by over 25 percent in the last six years.
    • NOx emissions are reduced by using low NOx combustors and selective catalytic reduction (SCR) or non-selective catalytic reduction (NSCR) in the smokestacks.
  • Emissions from motor vehicles, airplanes, power plants and industries.
    • Since the mid-1970s, two important features have been added to automobiles - catalytic converters and electronic fuel injection (EFI). Catalytic converters are located in the exhaust system to remove NOx emissions. EFI controls the formation of NOx emissions during combustion of the fuels.
    • Starting in 1996, automobiles have been equipped with onboard diagnostics (OBDII). This equipment signals the driver when the emission controls are not working, causing the car to create more pollution.
    • Changes continue to be to reduce the amount of sulfur in vehicle fuels. Cars using low-sulfur fuels emit less SO2 and NOx. This is because catalytic converters work more efficiently with low-sulfur fuel.
  • Emissions of SO2 and NOx from the Midwest.
    • The Clean Air Interstate Rule (CAIR) and the Acid Rain Program (ARP) were both cap-and-trade programs designed to reduce emissions of SO2 and NOx from power plants. EPA's Cross-State Air Pollution Rule (CSAPR) (leaves DEC) has replaced CAIR and began implementation on January 1, 2015.
    • The CSAPR requires a total of 28 states in the eastern half of the U.S. to improve air quality by reducing power plant emissions that cross state lines. This pollution can contribute to smog (ground-level ozone) and soot (fine particle pollution) in other states.

Effects of Acid Rain on the Environment

Aquatic - Freshwater macroinvertebrates, plants, and fish populations are damaged when acidic water disrupts their reproductive cycle. Aluminum leaches from the soil into the water, altering the chemistry and clogging the fish's gills. As water bodies become acidified, one species after another disappears. In addition to sensitive lakes, the Adirondack region includes thousands of miles of streams and rivers that are also sensitive to acidic deposition.

A loon with a hatchling riding on its back

Wildlife - Acid rain lowers the biological productivity of lakes and reduces the amount of forage fish available to loons. Toxicity from mercury pollution of water bodies can lead to decreased reproductive success of loons as well.

A forest

Forests - Sulfur and nitrogen deposition have caused adverse impacts on highly-sensitive forest ecosystems, especially the high-elevation, spruce-fir forests in the eastern United States. Forests are damaged because acid precipitation drains nutrients from the soil. Excess nitrogen in the air also may adversely affect tree growth. Evidence of decreased growth and dieback has been found in the Adirondacks.

Visibility - The same pollutants that cause acid rain can degrade air quality and significantly reduce visibility, even in remote areas like the Adirondack Mountains.

SUNY headquarter

Architecture - For buildings, bridges and cultural resources, acid deposition can cause damage. The sulfuric acid can have a corrosive effect on limestone and marble buildings and sculptures. Dry deposition can even be more damaging to stone than wet deposition for these structures.

Human Health - Walking in acid rain is no more dangerous to people than walking in non-acid rain. However, the pollutants that cause acid rain can be harmful to people. SO2 and NO2 can react in the atmosphere to form fine sulfate and nitrate particles. These particles can enter the lungs and cause lung disease, heart attacks, and difficulties for people with asthma. Acidified water can also cause metals to be leached from the soil into streams, lakes and reservoirs or old lead and copper pipes into home water supplies, causing serious illness.

Things You Can Do to Help

  • Conserve energy in your home and office.
  • Utilize public transportation, car pool, or walk.
  • Buy clean electric power.

New York's Acid Deposition Monitoring Network

brook trout in lake

New York's first acid deposition program was established in 1985 in response to the State Acid Deposition Control Act (SADCA). This program was designed to measure acid deposition to assess the effectiveness of sulfur control policies and other strategies aimed at reducing the effects of acid rain. The program has documented environmental improvements resulting from NOx and SOx control strategies. For example, the deposition of sulfate statewide has decreased by more than 75% since the monitoring program began. And these concentrations of acidic pollutants continue to decline. The SADCA established an environmental threshold value of 20 kg/ha/yr for wet sulfate deposition. Currently all monitoring sites in New York are well below that threshold.

At the end of 2012, the Department discontinued this program and transitioned six monitoring locations to the National Atmospheric Deposition Program (NADP) (leaves DEC website). The transition to the NADP program has provided data for use in regulation development. The NADP has also allowed for the comparison of data from New York with other acid sensitive regions across the country. NADP sites within New York and in neighboring states can better understand acid deposition across the northeastern US.

The NADP program measures the concentrations of free acidity (H+ as pH), conductance, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), sulfate (SO42-), nitrate (NO3- ), chloride (Cl- ), and ammonium (NH4+).

Data and reports from this program from across the United States can found on the NADP webpage (see "Links Leaving DEC's Website").

Adirondack Long Term Monitoring Program

Over the years, many programs and policies, have reduced emissions of pollutants that acidified clouds, fog, snow, sleet, and rain. One such program is the Adirondack Long Term Monitoring (PDF) Program (link leaves DEC). The ALTM has been documenting changes in the chemistry of lakes, streams, and clouds in the Adirondack Mountains since the 1980s.

More than 20 chemical parameters are measured in each ALTM water sample. These include sulfate (SO42-) and nitrate (NO3-), acid neutralizing capacity (ANC), pH, and toxic inorganic monomeric aluminum (Al), all are important indicators of lake ecosystem health. Research has shown that fish and other aquatic life are less resilient when exposed to certain chemical conditions. An example of some of these conditions are an ANC below 20 microequivalents per liter (µeq/L), pH below 6, and inorganic monomeric Al above 2 micromoles per liter (µmol/L). These conditions are most likely to occur during the spring snowmelt, generally March through April.

Acid-forming air pollution has declined since the 1980s. As a result, Adirondack lakes and streams are beginning to recover. For example, the acidity level in Brooktrout Lake, thought to be fishless by the mid-1980s, has decreased about 90% since the Adirondack Lakes Survey Corporation began monitoring this lake in 1992. Brooktrout Lake is now able to support self-sustaining brook trout populations. The DEC and its ALTM partners will continue this important program to support key environmental policy efforts even as new stressors, such as climate change, emerge. More information about this can be found in the August 2014 Conservationist (PDF) article titled "Coming Full Circle".

Monitoring SO2 in the Adirondacks

The DEC collects hourly SO2 data in the Adirondacks as part of the monitoring network created for the NYS Acid Deposition Control Act. Over 30 years data have shown consistent declines in SO2 connected with reductions in emissions both within and upwind of New York State. One recent result of this decrease is that the continuous monitoring method is now inadequate in rural areas. Continuous SO2 instruments were designed to produce data that can be compared to the higher levels relevant for the NAAQS.A large poster containing our data review over the period 2008-2017 is available below.

Poster showing SO2 data results, sites, and measurements for the Adirondacks for the period 2008-2017
Click to see large image

More about Acid Rain:

  • Acid Deposition Large Graphic - Detailed graphic of acid deposition
  • Review of 2008-2017 S02 Data in the Adirondacks - The NYSDEC collected hourly SO2 data at four locations in the Adirondacks as part of the monitoring network set up after the NYS Acid Deposition Control Act was signed in 1984. The three plus decades of SO2 data have shown consistent declines in concentration well correlated with reductions in emissions both within and upwind of New York State.