Baxter State Park, Maine: the Knife Edge Trail at the north end of the Appalachian Trail

Acid Precipitation

Identifying the Problem

• First warnings– Adirondacks

• 1970s?– Brenner pass

• Early 1980s– Eastern Canada

• Early 1980s– Smoky Mountains

• Mid-1980s– Worldwide

• 1990s

Identifying the Cause

• Disease• Weather• Pests

– Insects– Fungi

• Pollutants– Local vs distant

Chemistry of Acid Precipitation

• S + O2 --> SO2

• SO3 + H2O --> H2SO4

• N + O2 --> NO2

• NO2 + H2O --> HNO3

Acid Precipitation

http://www.physicalgeography.net/

Origins of the Problem

• 1950s effort to clean up local air– Lethal smogs

• Donora • London

• Solution: higher chimneys– The solution to pollution is dilution

• Consequences: – Diffusion of pollutants high into the troposphere– Long-range transport of gases, vapors

Effects on Natural Environments

• Terrestrial– Soils

• Buffering capacity of soil• Available nutrients

– Leaching• Type of plant

– Perennial vs annual– Foliage cycle– Plant parts are affected

differently• Leaves• Roots

• Aquatic effects– pH– Metals

• 1990s Nay Sayers

• UIUC crop scientist– Illinois soil pH has not

changed– Crops are not suffering– No problem!

• Reagan administration• Coal industry

Effects on Human Artifacts

• Metal• Fabrics• Stone

– Limestone

1908 1968

http://www.whatischemistry.unina.it

http://gardenofeaden.blogspot.com

Politics of Acid Precipitation• Source

– Example: NY Adirondack mountains• 50% of air pollution is

local– Cars– Manufacturing

• 50% is from distant sources

– Midwestern power plants

• Arguments against Mitigation– too expensive– Industry:

• $1,000-$1,500 per Ton sulfur• $2.4-5 billionannual cost

– EPA:• $6 billion/year?

• Legislation: – Clean Air Act, 1990

• signed by GHW Bush• reduce annual S deposition by

10,000,000 T from 1980 levels– 2 phases

• 1995 mostly coal-fired power plants

• 2000 - stricter limits on all plants• Use of “cap and trade” to achieve

decreases without damaging productivity

– Monitoring of acid deposition throughout

• Costs:– $100-200 / Ton sulfur dioxide– Total annual costs: 836,000,000

• PS: there were also cuts in particulates– decreased risks for asthmatics, etc– decreased atmospheric haze

The actual cost of residential electricity in the US, 1991-2010, depended more on the economy than on acid rain mitigation

Deposition of sulfur as sulfate: kg/ha/yr

Hydrogen ion deposition in the US: 1995 (left) and 2010 (below)H+ ion levels in kg/Ha

Summary

• Acid precipitation is a special case of air pollution• Air pollution affects living and non-living systems adversely• Controlling air pollution costs money

– but not as much as opponents predict• Not controlling air pollution is more expensive in the long run

– and we haven’t even talked about• incommensurables and • intangibles

• One more example of the importance of societal decisions vs laboratory data

Absolutely doable, and very safe – IFF you stay on the trail, which is unmistakably marked.