Mrs. Sealy APESMrs. Sealy APES

VII. Acid DepositionVII. Acid Deposition

• 1. “dilution solution” to air-pollution: to 1. “dilution solution” to air-pollution: to reduce local air pollution and meet reduce local air pollution and meet government standards without having to government standards without having to add expensive pollution control devices, add expensive pollution control devices, most coal-burning plants, ore smelters, most coal-burning plants, ore smelters, etc. use taller smokestacks to emit etc. use taller smokestacks to emit sulfur dioxide high into atmospheresulfur dioxide high into atmosphere

• 2.    increases pollution downwind2.    increases pollution downwind

VII. Acid DepositionVII. Acid Deposition

• 3. chemicals reach ground:  3. chemicals reach ground: 

• a. Wet: acid rain, snow, fog, cloud vapor a. Wet: acid rain, snow, fog, cloud vapor

• b. Dry:acidic particles b. Dry:acidic particles

• c. mixture causes acid deposition (acid c. mixture causes acid deposition (acid rain) rain)

VII. Acid DepositionVII. Acid Deposition• 4. pH: a numerical measure of the 4. pH: a numerical measure of the

concentration of hydrogen ions in a solution concentration of hydrogen ions in a solution (1 digit change equals 10X change in acidity)(1 digit change equals 10X change in acidity)

• a. levels less than 7 - acid (natural a. levels less than 7 - acid (natural precipitation) precipitation)

• b. levels greater than 7 - Baseb. levels greater than 7 - Base• c. typical rain in east US c. typical rain in east US is now about 10 times is now about 10 times more acidic (pH 4.3) more acidic (pH 4.3)

Wind

Transformation tosulfuric acid (H2SO4)and nitric acid (HNO3)

Nitric oxide (NO)

Acid fog

Ocean

Sulfur dioxide (SO2)and NO

Windborne ammonia gasand particles of cultivated soilpartially neutralize acids andform dry sulfate and nitrate salts

Dry aciddeposition(sulfur dioxidegas and particlesof sulfate andnitrate salts)

Farm

Lakes indeep soilhigh in limestoneare buffered

Lakes in shallowsoil low inlimestonebecomeacidic

Wet acid deposition(droplets of H2SO4 andHNO3 dissolved in rainand snow)

Fig. 17.9, p. 428

5. What areas are most affected 5. What areas are most affected by acid deposition? by acid deposition? • occurs on a local rather than global basis b/c occurs on a local rather than global basis b/c

acidic components only remain in the air for a acidic components only remain in the air for a few days few days

• areas downwind from coal and oil burning areas downwind from coal and oil burning power plants, industrial plants and urban power plants, industrial plants and urban areas areas

• ecosystems containing acidic soils without ecosystems containing acidic soils without natural buffering of bases natural buffering of bases

• growing problem in China (40% of its land), growing problem in China (40% of its land), former Soviet Union, India, Nigeria, Brazil, former Soviet Union, India, Nigeria, Brazil, Venezuela, Columbia Venezuela, Columbia

Potential problem areasbecause of sensitive soils

Potential problem areas because of air pollution: emissions leading to acid deposition

Current problem areas(including lakes and rivers) Fig. 17.11, p. 429

6. What are the effects of acid 6. What are the effects of acid deposition? deposition? •   medium-risk ecological problem, high-risk to medium-risk ecological problem, high-risk to

human health human health • human respiratory diseases (bronchitis, human respiratory diseases (bronchitis,

asthma), damages statues, buildings, metals, asthma), damages statues, buildings, metals, plastics and paintsplastics and paints

• damages tree foliage, makes trees more damages tree foliage, makes trees more susceptible to cold temps, disease, insects, susceptible to cold temps, disease, insects, drought, fungi drought, fungi

• harmful to aquatic species harmful to aquatic species

Emissions

Effects of Weather

Aciddeposition

Dryweather

Lowprecipitation

Increasedevapotranspiration

Increasedtranspiration

LakeGroundwater

SO2 NOX

H2O2 O3

PANs Others

Increasedsusceptibility

to frost,pests, fungi,

mosses,and disease

Dead leavesor needles

Reducedphotosynthesis

and growth

Tree deathDamageto treecrown

Waterdeficit

Nutrientdeficiency

Bark damage

Direct damageto leaves

and needles

Leaching ofsoil nutrients

Acidsand soilnutrients

Damage tofine roots Disturbance

of wateruptake

Disturbanceof nutrient

uptake

Soil acidification

Kills certainessential soil

microorganisms

Release of toxic metal ions

Nit

rate

Su

lfa

te

Ma

gn

es

ium

Alu

min

um

Ca

lciu

m

Po

tas

siu

m

Ac

ids

Fig. 17.14, p. 432

D. What can be done to reduce D. What can be done to reduce acid deposition? acid deposition? • preventionprevention• 1) reducing energy use & thus air-pollution by 1) reducing energy use & thus air-pollution by

improving energy efficiency improving energy efficiency • 2) switching from coal to cleaner-burning natural gas 2) switching from coal to cleaner-burning natural gas • 3) removing sulfur from coal before it is burned 3) removing sulfur from coal before it is burned • 4) burning low-sulfur coal4) burning low-sulfur coal• 5) removing SO2 particles, particulates, and nitrogen 5) removing SO2 particles, particulates, and nitrogen

oxides from smokestack gases oxides from smokestack gases • 6) removing nitrogen oxides from combustion 6) removing nitrogen oxides from combustion

enginesengines

D. What can be done to reduce D. What can be done to reduce acid deposition? acid deposition? • reducing coal use is economically & reducing coal use is economically &

politically difficult politically difficult • clean-up approaches are expensive and clean-up approaches are expensive and

mask symptoms w/ out treating causes mask symptoms w/ out treating causes • acidified lakes can be neutralized by treating acidified lakes can be neutralized by treating

them or the surrounding soil with large them or the surrounding soil with large amounts of limestone or lime. This is an amounts of limestone or lime. This is an expensive and temporary remedy expensive and temporary remedy