E2 Acid Deposition Rain Water E2.1 State what is meant by Acid deposition and Outline Its origins
E 2 Acid Deposition E2.1Statewhat is meant by Acid deposition and Outline Its origins Acid Deposition: The Problem Continues What Ever Happened to Acid Deposition?
In the 1980s, acid rain received a lot of media attention. What is Acid Deposition? How Does it Form?
Acidic particles and gases that deposit on earth as precipitation by rain, fog, snow Includes wet deposition of acidic gases NOx and SOx Dry deposition of acidic gases and particles in absence of rain Acid Deposition Precipitation with a pH lower than 5.6 is considered acidic 2.5 x mol dm-3 [H+] due to dissolved CO2 in water vapor Carbonic Acid CO2 (g) H2O (l) H2CO3(aq) H2CO H+ (aq)+ HCO3-(aq) Acid Rain pH is a logarithmic scale
One pH unitcorrespond to factor of 10 Compare pH 5.6 and pH 4.2 pH 4.2 has 25 times more H ion concentration Acid rain: pH 4 5 is common Acid Rain in Los Angles pH = 1.7 1982 Dec
Oxides of N, S ( non-metals) /cause of acid deposition Snow, fog, sleet, hail, drizzles become acidic in presence ofS, N oxides Los Angles Acid Rain Dead Lakes in North America, China, Russia; pH 4.0
Kills fish pH could be measured by pH paper, pH meter, universal indicator Origin of Acid Rain from sulfur dioxide and nitrogen oxide particles
Once these particles are emitted into the air they form sulfate and nitrate particles These particles can travel long distances on wind currents By combining with water vapor, these particles form acids which fall to the earth as acid rain.: fog, sleets, hail, drizzles Where do Sulfur Dioxide (SO2) and Nitrogen Oxide (NOx) Particles Come From?
Sulfur dioxide and nitrogen dioxide particles are emitted from utility plants, especially coal-fed electric plants Automobiles also emit acid rain causing pollution Formation Of Acid Deposition
In the presence of moisture, Soxproduce Acids SO2(g) +H2O(l) H2SO3(aq) Weak acid SO2(g) + O2(g) SO3(g) 2SO2(g) + O2(g)+ 2H2O(l) H2SO4(aq) SO3(g) +H2O(l) H2SO4(aq) Strong acid Acid Deposition : Nitrogen Oxides
NO2 gas: reddish-brown Poisonous, highly reactive 4 NO2(g) + 2 H2O(l) + O HNO3(aq) 2 NO2(g) +H2O(l) HNO3(aq) HNO3(aq) NO2(g) OH (g) HNO3 (aq) Formed during photochemical smog E 2.2 Environmental Effects
Affects humans and aquatic life Dissolution of limestone Corrosion of metals Deterioration of electrical equipment Vegetation, soil, visibility 1. Effects of Acid Rain on Humans
Respiratory system irritation by breathing fine acid droplets Severe eye irritation Sulfate aerosol are powerful irritants Penetrates lungs/ remain embedded and have severe asthmatic effect on young and elderly Effects on Humans due to acidic conditions Alzheimer disease
Increased concentration of Al 3+ in water due to acidic conditions Alzheimer disease Effect on Aquatic life Kills fish,
At pH 5, most fish eggs cannot hatch. Salmon can not survive in pH ~ 5.5 Increase concentration of Al3+ ions affects the function of the gills. Al3+ ions come from leaching of soil by acidic rain Effect on Aquatic life Eutrophication : Nitrates from acid deposition Effect on materials Corrosion of basic materials, limestone and dolomite CaCO3MgCO3 CaCO3(s) +H2SO4(aq) CaSO4(aq) H2O(l) CO2(g) Sulfates can dissolve in water Structural damage / stone leprosy Egin Egypt, Greece, Mexico, Turkey Effect on materials Corrosion of iron and steel promoted by acid rain
with increased humidity, high temperature, presence of particulates 4 Fe(s) + x H2O(l)+ 3O2(g) 2 Fe2O3.xH20(s) Effect on materials Deterioration of electrical equipment as a result of corrosion Bleaching and weakening of paperfabric, leather Leach heavy metals such as lead, cadmium and mercury in water system Environmental Effects
Bleachingand weakening of fabric and leather Discoloration of paper Acute and chronic effects on plants Significant decrease in crop yields Material Damage carbon-steel, nickel, zinc, copper, paint,
some plastics, paper, leather and textiles. Stainless steel and aluminum are more resistant to acid rain. Material Damage Structural damage to underground pipes, cables
and foundations submerged in acid waters can also occur, in addition to damage to buildings, bridges and vehicles above ground Effect on Soil and Vegetation
Plants damage by acidconcentration Length of exposure Acute injury due to short term exposure to high conc. Acid rain Attack on cells producing dead leaves Effects on Vegetation Chronic injury
Long term exposure to even low acid concentration Disrupts chlorophyll synthesis Yellowing of leaves due to acid entering stomata of leaves Bleached spots, suppression of plant growth, reduction in yield Effects on Vegetation Removes important nutrient from soil Eg. Mg 2+
It is an essential mineral nutrient for life[1][2][3] and is present in every cell type in every organism. Chlorophyll Mg 2+ chlorophylls : effective photoreceptors
contain a network of alternating single and double bonds, ( conjugated) Electron candelocalize stabilizing the structure. Such delocalized poly-enes have very strong absorption bands in the visible regions of the spectrum, allowing the plant to absorb the energy from sunlight. Effects on visibility Mist of sulfuric acid and sulfate aerosol cause great loss of visibility Curtail air flights Aerosol particles modify Earth's radiation budget. They are also linked to adverse health effects. atmospheric particles enriched in sulfate (green) and methane sulfonate (blue) typical for a marine environment Relative humidity Controlling Acid Deposition
Reduction of SOX and NOX Reduction of SO2 emission: E1.2 Use of catalytic convertor Lean burn engines . use of low sulfur, cleaner burning coal Anthracite / high heat content Coal low grade( sub bituminous) coal and lignite of low sulfur content does not produce much heat due to lower carbon content ( ~ more of coal needs to burn) 2.Coal to SNG Conversion process allows removal of SO2
30 % energy required Cleaning Coal Before combustion / pre combustion
Coal is finely ground and washed with water Iron pyrite settles down because of higher density Organic sulfur can not be removed Process is expensive (50 % S removal ) 4.Post Combustion Method
Lean burn engine Catalytic converter CO (g) NO(g) CO2(g) +N2 Using Limestone fluidizedbeds Alkaline scrubbing Promoting use of alternative energy sources
Solar, wind, fuel cells, hybrid automobiles Increased public transportation Addition of lime to soil and lakes to neutralize acidity Can We Do Anything About Acid Rain?
YES! We can all take small actions to help solve the problem We can help by: using our cars less conserving electricity choosing electricity providers that emit lower amounts of air pollution emissions How Does Acid Rain Effect Our Lives?
Poor forest health due to acidification of soil: acid rain can kill nutrient-producing microorganisms Acidification of lakes and streams can lead to the death of aquatic life, such as trout and bass Acidity can leach mercury out of the soil, causing toxic levels to build up in the fish we eat Acid rain can erode buildings and monuments and destroy paint finishes What else needs to be done about Acid Rain ?
In 1990, an amendment to the Clean Air Act called for reductions in sulfur emissions This proved to be less effective than hoped, as acid rain still persists today This is largely due to 2 reasons: 1) reductions in sulfur emissions were not great enough and 2) there were no reductions in nitrogen emissions which are also implicated in forming acid rain What is Being Done About Acid Rain?
An International Acid Rain Steering Committee was formed and is currently discussing joint action to further reduce sulfur emissions by 50% and reduce nitrogen emissions by 30% by the year 2010 Ozone