RAIN WATER VS OCEAN WATERRAIN WATER VS OCEAN WATER

RAIN WATER is naturally acid due to the solubility of CO2 in water. (also O2 + N2)

CO2(g) + H2O(l) H2CO3(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

CO2 & H2O, it is neutralized by dissolved alkaline substances into

CaCO3. pH ~8.2

The products of neutralization end up on the ocean floor as insoluble solids.

H2CO3 + CaCO3 Ca (HCO3)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 CO2 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 SOX and NOX 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 DepositionDry 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 (SOx, NOx, particulates, etc.) absorbed by atmospheric moisture.

2SO2(g) + O2(g) 2SO3(g)

SO3(g) + H2O(l) H2SO4(ag)

- sulfuric acid is much stronger than carbonic acid

- sulfuric acid eventually corrodes metals, paints and other exposed substances

SOx AS AIR POLLUTANTS + O2 SO2 or 2H2S + 3O2 2SO2 + 2H2O

SO2 + 1/2O2 SO3 SO3 + H2O H2SO4 (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 H2SO4:- dissociates into H+, HSO4

- & SO42- a

strong acid and a weak acid

-

SOX Toxicity

SO2 toxic to plants 0.3 ppm for 8 hr causes severe damage to plants (choking effect)1 hr - 5ppm - severe construction of brochial tubes

H2SO4 - acid is dangerous buildings, art, and statuesCaCO 3 (marble) + H2SO4 CaSO4 + CO2 + H2O,

Fe + H2SO4 FeSO4 + H2

CaCO3 - limestone SiO2 + Al2O3 = clay: cement CaSO4 · 2 H2O

H2SO4 - dangerous to plants, animals, oceans, forests and crops Acid rain changes the pH of lakes. This acid has a strong affinity for H2O that is, it removes H2O 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 HgS + O2 Hg + SO2 (CuS, Ag2S, ZnS, PbS) *industrial plants (81,000 tons per day of SO2) *wine industry (compounds used to kill fungi in barrels) *preservatives in fruit juices *bleaching agents *paper production *coal industry 4FeS2(s) + 1102 2Fe2O3(s) + 8SO2

SOx

H2SO4 AS A WATER POLLUTANT

Acid Mine drain:Pyrite (FeS2) occurs along with coal,

after mining operations, pyrite is exposed to moist O2 (weather)

4 FeS2 + 2 H2O + 15 O2 Fe2(SO4)3 + 2H2SO4

Unless controlled, acid drainage from coal mines can pollute

streams, killing fish and other wildlife.

In North East US 62% is H2SO4 32% HNO3 6% HCl

NATURAL SOURCES:- ~80% air is composed of N2 so actions like lightning storms produce Nox

- bacterial action

HUMAN SOURCES:- incomplete combustion of air- production of plastics, nylon, fertilizers and explosives.

NOx

NOx AS AIR POLLUTANTHeat + N2 + O2 2 NO• (radical)

NO• + 1/2 O2 •NO2

3•NO2 + H2O 2 HNO3 + NO• Acid rain

•NO2 is a brown toxic gas, affects respiratory system, chokes & damages lung tissue.

Nitric Acid is a problem due to the abundance of N2 in air. It readily reacts with metals to produce NO2 which continues the cycle.

Fe + 6HNO3 Fe (NO3)3 + 3•NO2 + 3H20 3•NO2 + H2O 2HNO3 + •NO cyclic

Table 6.1 Estimated Global Emissions of Sulfur and Nitrogen Oxides (in millions of metric tons per year)

Source SO2* Nox** Natural:

Oceans 22 1Soil and plants 2 43Volcanoes 19Lightning __ 15Subtotals 43 59

Anthropogenic:Fossil Fuels combustion 142 55Industry (mainly ore smelting) 13Biomass burning 5 30Subtotals 160 85

TOTALS 203 144Sources: *Data from Spiro, et al. “Global inventory of sulfur emissions with 1º X 1º resolution” in Journal of Geophysical Research, 97, No. D5, 6023, 1992.**United States Environmental Protection Agency, Air Quality Criteria for Oxidesof 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