RAIN WATER VS OCEAN WATER RAIN WATER is naturally acid due to the solubility of CO 2 in water. (also O 2 + N 2 ) CO 2(g) + H 2 O (l)  H 2 CO 3(ag) Carbonic Acid PH ~ 5.6 (normal range = 5 to 7 pH) The natural acidity of rain water promotes the erosion of land, the formation of underground caves, and maintenance of the nitrogen cycle.

Rain Water vs. Ocean Water OCEAN WATER also contains carbonic acid but instead of reverting back into CO 2 & H 2 O, it is neutralized by dissolved alkaline substances into CaCO 3. pH ~8.2 The products of neutralization end up on the ocean floor as insoluble solids. H 2 CO 3 + CaCO 3  Ca (HCO 3 ) 2  The ocean acts as a sink and does not allow CO2 to be released back into the atmosphere.

ACID RAIN Natural rain contains some dissolved CO 2 gas from the atmosphere, making rain slightly acidic ~ 5.6 pH. Acid rain refers to rain that has a pH lower than natural rain. pH  5.6 In the US, Acid rain has a pH  4 due to dissolved SO X and NO X gases. Different regions of the U.S. experience different acid rain.

Where is it a problem? Acid rain is a problem in eastern America because many of the water and soil systems in this region lack natural alkalinity - such as a lime base - and therefore cannot neutralize acid naturally.

What exactly is acid rain? "Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.

Wet deposition Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water.

Dry Deposition Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone.

How does Acid Rain happen? Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid.

ACID RAIN pH < 5 - created by airborne pollutants (SO x, NO x, particulates, etc.) absorbed by atmospheric moisture. 2SO 2(g) + O 2(g)  2SO 3(g) SO 3(g) + H 2 O (l)  H 2 SO 4(ag) - sulfuric acid is much stronger than carbonic acid - sulfuric acid eventually corrodes metals, paints and other exposed substances

SO x AS AIR POLLUTANT S + O 2  SO 2 or 2H 2 S + 3O 2  2SO 2 + 2H 2 O SO 2 + 1/2O 2  SO 3 SO3 + H 2 O  H 2 SO 4 (acid rain) Produces Aerosols which are suspensions of tiny droplets of liquid in a gas. A suspension of solid in a liquid is called a colloid. General Information about H 2 SO 4 : - dissociates into H +, HSO 4 - & SO 4 2- a strong acid and a weak acid -

SO X Toxicity SO 2 toxic to plants 0.3 ppm for 8 hr causes severe damage to plants (choking effect) 1 hr - 5ppm - severe construction of brochial tubes H 2 SO 4 - acid is dangerous buildings, art, and statues CaCO 3 (marble) + H 2 SO 4  CaSO 4 + CO 2 + H 2 O, Fe + H 2 SO 4  FeSO 4 + H 2 CaCO 3 - limestone SiO 2 + Al 2 O 3 = clay: cement CaSO 4 · 2 H 2 O H 2 SO 4 - dangerous to plants, animals, oceans, forests and crops Acid rain changes the pH of lakes. This acid has a strong affinity for H 2 O that is, it removes H 2 O from organic materials or dehydrates.

NATURAL SOURCES: - geothermal emission - biological processes (marine & anaerobic bacteria) - volcano eruptions HUMAN SOURCES: - combustion of fossil fuels (autos, electricity, power plants, space heating, industry) - non combustion sources: *metal ore smelting plants H g S + O 2  H g + SO 2 (C u S, A g2 S, Z n S, P b S) *industrial plants (81,000 tons per day of SO 2 ) *wine industry (compounds used to kill fungi in barrels) *preservatives in fruit juices *bleaching agents *paper production *coal industry 4FeS 2(s)  2Fe 2 O 3(s) + 8SO 2 SO x

H 2 SO 4 AS A WATER POLLUTANT Acid Mine drain: Pyrite (FeS 2 ) occurs along with coal, after mining operations, pyrite is exposed to moist O 2 (weather) 4 FeS H 2 O + 15 O 2  Fe 2 (SO 4 ) 3 + 2H 2 SO 4 Unless controlled, acid drainage from coal mines can pollute streams, killing fish and other wildlife. In North East US 62% is H 2 SO 4 32% HNO 3 6% HCl

NATURAL SOURCES: - ~80% air is composed of N 2 so actions like lightning storms produce No x - bacterial action HUMAN SOURCES: - incomplete combustion of air - production of plastics, nylon, fertilizers and explosives. NO x

NO x AS AIR POLLUTANT Heat + N 2 + O 2  2 NO (radical) NO + 1/2 O 2  NO 2 3NO 2 + H 2 O  2 HNO 3 + NO Acid rain NO 2 is a brown toxic gas, affects respiratory system, chokes & damages lung tissue. Nitric Acid is a problem due to the abundance of N 2 in air. It readily reacts with metals to produce NO 2 which continues the cycle. Fe + 6HNO 3  Fe (NO 3 ) 3 + 3NO 2 + 3H 2 0 3NO 2 + H 2 O  2HNO 3 + NO cyclic

Table 6.1 Estimated Global Emissions of Sulfur and Nitrogen Oxides (in millions of metric tons per year) SourceSO 2 *No x ** Natural: Oceans 22 1 Soil and plants 2 43 Volcanoes 19 Lightning __ 15 Subtotals Anthropogenic: Fossil Fuels combustion Industry (mainly ore smelting) 13 Biomass burning 5 30 Subtotals TOTALS Sources: *Data from Spiro, et al. “Global inventory of sulfur emissions with 1º X 1º resolution” in Journal of Geophysical Research, 97, No. D5, 6023, **United States Environmental Protection Agency, Air Quality Criteria for Oxides of Nitrogen, EPA/600/8-91/04aA.

What are acid rain effects? damage to forests and soils, fish and other living things, materials, and human health reduces how far and how clearly we can see through the air Acid rain does not only effect organisms on land, but also effect organisms in aquatic biomes. Most lakes and streams have a pH level between six and eight. Some lakes are naturally acidic even without the effects of acid rain.

Effects on human causes toxic metals to break loose from their natural chemical compounds toxic metals that might be absorbed by the drinking water, crops, or animals that human need