Acid Deposition

Locations and Effects

Fall 2012, Lecture 10

1

What is Acid Deposition?

• Acid deposition consists of delivery of acidic substances, mainly sulfur and nitrogen oxides, acids and salts, through the atmosphere to the earth's surface

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Acid Rain Graphic

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Sources of Acid Deposition

• These compounds (principally the oxides) are introduced into the atmosphere as by-products of combustion and industrial activity, at rates which greatly exceed natural emission rates in industrialized areas such as eastern North America

• Acid deposition also includes contributions from natural sources and deposition of other acidic compounds, but these contributions are relatively minor

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U.S. SO2 Sources, 2008

• Electric generation is by far the largest source of SO2 in the U.S.

• Most of this is from coal-fired power plants

• U.S. total is about 7x greater than Canada

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Canadian SO2 Sources, 2008

• Canadian SO2 emissions come mostly from the nonferrous smelting and refining industry, the upstream petroleum industry and electric power generation utilities

• The contribution from electric power generation utilities is lower in Canada due to the large hydroelectric and nuclear capacity in place

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Long-term SO2 Trends

• Both countries have reduced SO2 emissions, Canada by 47% since 1990, and the U.S. by 51%

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Annual SO2 Emissions, 1990 - 2010

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U.S. NOx Sources, 2008

• The distribution of NOx emissions in the two countries is similar, with non-road and on-road vehicles accounting for the greatest portion of NOx emissions

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Canadian NOx Sources, 2008

• U.S. Sources are about eight times greater than Canada, reflecting the much greater number of vehicles in the U.S.

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Long-term NOx Trends

• U.S. has improved more than Canada

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Annual NOx Emissions, 1990 - 2010

2008 data are preliminary

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International Cooperation

• Both Canada and the United States committed to reduce the impact of transboundary air pollution through the 1991 Canada–United States Air Quality Agreement (AQA)

• The Acid Rain Annex, negotiated with the original 1991 agreement, committed both Canada and the United States to reducing acid rain-causing emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx)

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AQA Addendum

• The Ozone Annex, added to the Agreement in 2000, committed both countries to reducing emissions of NOx and volatile organic compounds (VOCs), the precursors to groundlevel ozone, a key component of smog

• Between 2000 and 2008, the United States has reduced NOx emissions by 33% in the transboundary ozone region while Canada’s total NOx emissions decreased by 32% in the region.

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Deposition Processes• Delivery of material to the earth's

surface by precipitation processes is "wet deposition”

• Direct uptake processes at the earth's surface involving turbulent mixing or settling of gases and particles followed by absorption, adsorption, adhesion, or impaction is "dry deposition"

• The direct impact of acidic cloud or fog droplets on vegetation or other surfaces also contributes to acid deposition

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Systems Affected by Acid Deposition

• Aquatic systems (lakes, rivers)

• Vegetation

• Human health

• Human economic livelihood

• Inanimate objects built by humans

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How is Acidity Measured?

• Acidity is measured using the pH scale

• pH = - log [H+] , [H+] is the hydrogen ion concentration

• Examples: If [H+] = 10-7, then: pH = - log [10-7] = -(-7) = 7

• A pH of 7 is neutral, pH less than 7 is acidic, and pH greater than 7 is alkaline

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Why pH?

• The term pH comes from the French, “pouvoir Hydrogene”, which means power of hydrogen

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Log Scales

• An increase of one log unit corresponds to an increase of ten in the quantity measured

• Thus, pH 4 is ten times more acidic than pH 5• Normal rain has a pH of about 5.5• The most acidic rain in the United States in 2000

had a pH of 4.3• The pH of rain in Ontario’s Muskoka-Haliburton

area ranges between 3.9 and 4.4

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pH

• pH levels of various substances

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Aquatic Systems

• Acid deposition can lower pH

• Bedrock of stream or lake and the surrounding watershed determines the susceptibility to acid deposition

• Susceptible systems show a decline in fish populations

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Acidified Lakes

• Contain high concentrations of toxic heavy metals like mercury, aluminum, and cadmium

• Soil and bedrock surrounding the water body is the source of the toxic metals

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Acid Shock• Occurs in mid-latitudes where snow accumulates

in winter• Acidic deposits can build-up in the snowpack• When spring arrives, snowpack begins to melt

quickly• Acids are released over a short period of time at

concentrations 5 to 10 times more acidic than rainfall

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Gradual Acidification

• Gradual decline in pH – no acid shock

• Prolonged acidity interferes with fish reproduction and spawning

• Over time, a decrease in fish population density and a shift in the size and age of the population to older and larger fish occurs

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Effects on Aquatic Plants

• Alterations in the composition and structure of the aquatic plant communities

• In experimental studies, differences in nutrient level(phosphorous and nitrogen) appeared to be the limiting factor

• Reductions in biodiversity

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Aquatic Microorganisms

• Acidification reduces microbiological activity Reduces rates of decomposition and the

accumulation of organic matter in aquatic ecosystems

• Reduces nutrient recycling

• Reduces energy available to biologic systems

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Effects on Vegetation • Severity of acid deposition on vegetation is

greatly dependent on the type of soil the plants grow in

• Many soils have a natural buffering capacity and are able to neutralize acid inputs

• Limy soils are better at neutralizing acids than those that are made up of siliceous sand or weathered acidic bedrock

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Mt. Mitchell State Park, North Carolina

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Acid Rain Video

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Lime is a Buffer

• Lime is calcium carbonate

• Carbonates react with acids, neutralizing them

• As long as lime is available, the soil, and water in contact with it, cannot become overly acidic

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Why Acid Affects Unbuffered Soils

• Leaching of plants nutrients

• Declining growth rates

• Aluminum mobilization

• Inhibition of seed germination

• Inhibition of seedling growth

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Why Acid Affects Unbuffered Soils

• Soil organism mortality Inhibits decomposition and nutrient

recycling

• Nitrogen Saturation• Acid rain damages foliage• Dry deposition affects water retention• Acid leaches nutrients from plant tissues

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Overall Effects on Vegetation

• Combination of these effects can lead to plants that have reduced growth rates, flowering ability and yields

• Makes plants more vulnerable to diseases, insects, droughts and frosts

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Effects on Humans

• Release of toxic metals

• Respiratory illness

• Increased likelihood of chest colds, allergies, coughs, asthma

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Economic Impacts

• Decline in fishing Commercial Sport

• Damage to forests

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Effects on Construction

• Buildings, headstones, etc. constructed of limestone or marble may be dissolved

• Paint, especially automotive paint, may be damaged

• European churches and cathedrals have been damaged

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Lincoln Cathedral, England

• 1920 – After 400 years of weathering

• 1984 – after an additional 64 years

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Jefferson Memorial

• Marble surfaces exposed to rain develop a rough "sugary" texture because the calcite grains are loosened as the edges dissolve in the rain water

• Column capital volute, Jefferson Memorial, Washington, D.C.

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Acid Rain Video

• Discovery Acid Rain Presentation

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Sunland Park Mall El Paso, Texas

• Sunland Park Mall was built in 1989 of polished pink marble

• Much of the marble looks just as fresh today as on the day it was installed

• In some areas, however, the marble has badly deteriorated

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Sunland Mall Marble Closeup• Deterioration occurs where

sprinkler system repeatedly wets the marble

• Water dissolves the mineral calcite, the main mineral in marble

• Marble far above ground level still looks fresh

• Intensity of chemical weathering increases down toward the level of the bushes

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Sunland Mall Marble Closeup

• Weathering rate may be increased by fertilizers or other substances sprayed on the bushes

• Acidic fertilizers promote dissolution of marble 42

U.S. Acid Rain Program

• Title IV (the Acid Rain Program or ARP) of the Clean Air Act Amendments of 1990 requires major reductions of SO2 and NOx emissions from the electric power sector, the highest SO2 emitting sector

• Under the ARP, the SO2 program set a permanent cap on the total amount of SO2 that may be emitted by electric generation units in the contiguous United States starting in 1995

• The reductions are phased in over time, with the final 2010 SO2 cap set at 8.95 million tons

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U.S. Acid Rain Program Target

• Cut SO2 emissions by 50% from 1980 levels by 2010

• Improve visibility in eastern U.S. by 30%

• Increase “value” by more than $1 billion dollars annually by 2010

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U.S. Acid Rain Program Achievement

• The United States succeeded in meeting its commitment to reduce annual SO2 emissions by 10 million tons from 1980 levels by 2000.

• Additionally, in 2007, emissions of SO2 from the electric power sector in the United States fell below the 2010 national emission cap of 8.95 million tons for the first time, achieving the U.S. commitment three years early

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Visual Range

• “Standard visual range” is defined as the farthest distance a large dark object can be seen during daylight hours

• This distance is calculated using fine and coarse particle data from the IMPROVE network

• Increased particle pollution reduces the visual range• The visual range under naturally occurring conditions without human-

caused pollution in the United States is typically 45 to 90 miles (75 to 150 km) in the east and 120 to 180 miles (200 to 300 km) in the west

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Sulfate Aerosol Concentrations

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1989 2010

Nitrate Aerosol Concentrations

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1989 2010

Clean Air Act Difference

• Examination of the last three slides shows large improvements in both sulfate and nitrate from 1989 (just before the new Clean Air Act programs) to 2010 (latest available data)

• The Clean Air Act has clearly made a huge difference

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Ammonium Aerosol Concentrations

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1989 2010

Agricultural Air Pollution

• Ammonium comes primarily from agricultural application of fertilizer

• This is not regulated by the Clean Air Act• In the center of the country, ammonium

concentrations have risen• In the corn belt, the new agricultural practices

are having an effect (Wisconsin, Michigan, Indiana and parts of Minnesota and Iowa)

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Dry versus Wet

Deposition

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• The dry deposition component for sulfur varies between approximately 11%–60% at Eastern sites. The variation in dry sulfur deposition can be attributed to the proximity of large emission point sources in the Midwest region.

• Nitrogen deposition is typically more uniform across the East due to the large NOx

contribution from motor vehicles

The maps are regional aggregations of sulfur and nitrogen deposition at Eastern sites averaged over the 2003–2006 period

Clean Air Status and Trends Network(CASTNET)

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CASTNET Monitoring Procedures

• At each site, there is a temperature-controlled shelter which houses a computer, a data logger, and a continuous ozone monitor Weekly samples of particulate matter and select gasses are

collected using a 3-stage filter pack with a controlled flow rate located atop a 10m tower

For quality assurance, site audits are performed once every six months and biennially by the CASTNET contractor and a third party auditor, respectively

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CSAPR replaces CAIR and ARP

• The Clean Air Interstate Rule (CAIR) and the Acid Rain Program (ARP) are both cap and trade programs designed to reduce emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from power plants

• On July 6, 2011, EPA finalized the Cross-State Air Pollution Rule (CSAPR), which will replace CAIR starting in 2012

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Clean Air Interstate Rule

• The CSAPR will require 27 states in the eastern half of the U.S. to significantly improve air quality by reducing power plant emissions of SO2 and NOx that cross state lines and contribute to smog (ground-level ozone) and soot (fine particle pollution) in other states

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CSAPR Timetable

• The first phase of compliance begins January 1, 2012 for SO2 and annual NOx reductions and May 1, 2012 for ozone season NOx reductions

• Additional SO2 reductions are required by sixteen Group 1 states in 2014 to eliminate their contribution to downwind air quality problems

57

Acid Rain Program in Canada

• In 2008, Canada’s total SO2 emissions were 1.7 million tons, or about 47% below the national cap of 3.2 million tons

• This represents more than a 63% reduction from Canada’s total SO2 emissions in 1980 and a 46% decrease from the 1990 emission level

• This overall reduction in national SO2 emission levels can be attributed to the SO2 emission reductions undertaken by the four eastern provinces (New Brunswick, Nova Scotia, Quebec and Ontario) targeted by the Acid Rain Strategy

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Effect of SO2 Reduction on Climate

• The IPCC February, 2000 report increased the estimate of maximum temperature increase by 2100 to 5.8 degrees Celsius

• Maximum temperature increase due to reduction in SO2 haze, which reflects sunlight and cools the surface

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Ocean Acidification

• Another aspect of acid deposition is the acidification of the oceans

• Since man first began using fossil fuels, we have added carbon dioxide (CO2) to the atmosphere

• Atmosphere-ocean exchange transfers some of the CO2 to the ocean

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The Other Carbon Problem

• Many people are familiar with the idea that CO2 is a greenhouse gas, responsible for a significant increase in temperature

• The acidification of the oceans, due to the addition of CO2 from the atmosphere, is an equally significant, but much less well known, problem

• It is often called “The Other Carbon Problem”

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Chemistry

• The basic chemistry of CO2 addition is:

• CO2 + H2O = H2CO3

• Carbon dioxide + water = carbonic acid

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Dissociation

• Carbonic acid can dissociate to bicarbonate ion in water

• H2CO3 = HCO3-1 + H+

• Carbonic acid gives Bicarbonate ion plus hydrogen ion

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Further Dissociation

• Bicarbonate ion further dissociates

• HCO3-1 = CO3

-2 + H+

• Bicarbonate ion gives carbonate ion plus hydrogen ion

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Chemical Adjustments

• In the oceans, carbonic acid, bicarbonate ion, and carbonate ion are all present

• In most cases, they achieve chemical equilibrium

• This means the amount of each substance adjusts as conditions, such as temperature and pH, change

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Atmospheric CO2 versus Ocean pH

• The diagram shows that as the atmospheric CO2 increases (red) so does oceanic CO2

(dark blue)• The pH decreases

proportionately (light blue)

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Computer Animation of Acidification

• The movie (next slide) shows a computer recreation of surface ocean pH from 1895 to the present, and it forecasts how ocean pH will drop even more between now and 2094

• Dark gray dots show cold-water coral reefs

• Medium gray dots show warm-water coral reefs

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Ocean Acidification, 1895-2094

• You can see that ocean acidification was slow at the beginning of the movie, but it speeds up as time goes on

• This is because humans are releasing carbon dioxide faster than the atmosphere-ocean system can handle

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Omega

• Ocean acidification also decreases the number of carbonate ions in seawater

• Scientists often track ocean acidification by measuring “omega”

• This is the saturation state of calcium carbonate minerals, which is shown in the movie (next slide) and is important because carbonate ions are the building blocks that marine animals like corals, clams, and some algae use to make hard shells and skeletons

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Omega 1895-2094

• In this movie, areas with high omega and many carbonate ions for building shells and skeletons are in blue

• Areas with lower omega and fewer carbonate ions are in orange.

• Areas with the lowest omega, where calcium carbonate minerals will dissolve, show up in light gray.

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Effect on Coral Reefs

• Australian scientists discuss ocean acidification’s effects

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Google Earth Tour: Ocean Acidification

• “This Google Earth Tour, narrated by Dan Laffoley from the International Union for Conservation of Nature (IUCN), who is Chair of Europe's Ocean Acidification Reference User Group, takes us on a global journey to understand what impact carbon dioxide has on ocean chemistry. It explores the phenomenon of ocean acidification and explains why even small changes to ocean chemistry could have profound implications for marine life and future economic activities.”

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Google Earth Tour cont.

• “… first presented at the 3rd Symposium on the Ocean in a High CO2 World in Monterey in September 2012 and was prepared in partnership with Jenifer Austin Foulkes (Google), with script by Owen Gaffney (International Geosphere and Biosphere Programme) and Dan Laffoley. The animated sequence of ocean acidification through to the year 2300 was created using data provided by the Max Planck Institute for Meteorology www.mpimet.mpg.de (courtesy Dr. Tatiana Ilyina) and the visualization tools of the German Climate Computing Center www.dkrz.de (courtesy Dr. Michael Böttinger).”

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Google Earth Tour Video

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Acid Test: The Global Challenge of Ocean Acidification

• NRDC video featuring Sigourney Weaver, originally aired on Discovery Planet Green, copyright 2009 75