Presentation on theme: "Air pollutants from natural sources ~Volcano produces sulphur dioxide ~ Biological processes e.g. Digestion in cows produces large amounts of methane."— Presentation transcript:
Air pollutants from natural sources ~Volcano produces sulphur dioxide ~ Biological processes e.g. Digestion in cows produces large amounts of methane. Methane is an air pollutant
Air pollutants from human activities * cars burn petrol or diesel * power stations burn coal * factories burn heavy oil
Atmospheric pollutants 1. Carbon monoxide and carbon 2. Unburnt hydrocarbons 3. Sulphur dioxide 4. Oxides of nitrogen 5. Photochemical smog 6. Lead compounds and Heavy Metals 7. Particulates 8. Ozone 9. Benzene 10. 1,3-butadiene 11. TOMPs (Toxic Organic Micropollutants)
Carbon monoxide (CO) is a toxic gas emitted into the atmosphere by incomplete combustion processes formed by the oxidation of hydrocarbons and other organic compounds. survives in the atmosphere for a period of approximately 1 month is eventually oxidized to carbon dioxide (CO 2 ). Carbon particles are part of the dark smoke that forms. 1. Carbon monoxide and carbon
In urban areas, CO is produced almost entirely (90%) from road traffic emissions. CO at levels found in ambient air may reduce the oxygen-carrying capacity of the blood. Low conc.: dizzy, headache and irritable High conc.: unconsciousness and death
2.Unburnt hydrocarbons Two main groups of hydrocarbons : volatile organic compounds (VOCs) polycyclic aromatic hydrocarbons (PAHs). VOCs : released in vehicle exhaust gases emitted by the evaporation of solvents and motor fuels. Effect: `cause cancer `formation of smog (smoke + fog)
3. Sulphur dioxide Sulphur dioxide is a corrosive acid gas. Source : power stations burning fossil fuels which contain sulphur
Effect combines with water vapour in the atmosphere to produce acid rain. damage and destruction of vegetation and in the degradation of soils, building materials and watercourses SO 2 in ambient air is associated with asthma and chronic bronchitis SO 2 emissions effect air quality in both rural and urban areas Low conc. : respiratory tracts and lung diseases High conc. : cancer and death SO 2 (g)+H 2 O(l) H 2 SO 3 (aq) Sulphurous acid
4.oxides of nitrogen Nitrogen oxides ~formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. sources: power stations, heating plants and industrial processes. The principal source of nitrogen oxides : - nitric oxide (NO) - nitrogen dioxide (NO 2 )
Nitrogen oxides ~ mainly in the form of NO in the atmosphere N 2 (g)+O 2 (g) 2NO(g) ~ then oxidized to NO 2 by reaction with ozone 2NO(g)+O 2 (g) 2NO 2 (g)
Effect Irritation of respiratory tracts and lungs Exacerbate asthma Increase susceptibility to infections In the presence of sunlight, it reacts with hydrocarbons to produce photochemical pollutants such as ozone. Nitrogen oxides have a lifetime of approximately 1 day with respect to conversion to nitric acid. Nitric acid is in turn removed from the atmosphere by direct deposition to the ground, or transfer to aqueous droplets (e.g. cloud or rainwater), thereby contributing to acid deposition.
5. Photochemical smog Sunlight acts on air pollutants ( e.g. carbon monoxide, nitrogen oxides, hydrocarbons) * form a new substance called Photochemical smog
Effect Irritate the eyes dangerous to people with breathing and heart problems poisonous to plants damages rubber, paint and other materials
6. Lead compounds and Heavy Metals Particulate metals in air come from: fossil fuel combustion metal processing industries waste incineration Lead ~ is the most widely used non-ferrous metal ~ use world-wide is in the manufacture of batteries (60-70% of total consumption of some 4 million tonnes) ~ used in paints, glazes, alloys, radiation shielding, tank lining and piping.
Tetraethyl lead used as an additive in petrol to increase the octane number most airborne emissions of lead from petrol-engined motor vehicles.
Effect Lead is a cumulative poison to the Central Nervous System, particularly detrimental to the mental development of children. Harmful effects on red blood cells, kidney, bones, brain Heart attacks, stroke, hypertension and nervous disorder
7.Particulates PM10 particles ~the fraction of particulate in air of very small size <10 ~ removed relatively efficiently from the air by sedimentation. ~ primary ( emitted directly into the atmosphere) ~ secondary (formed or modified in the atmosphere from condensation and growth). The atmospheric lifetime of particulate matter ~as long as 10 days for particles of about 1mm in diameter
creating dirt, odour and visibility problems health effects :risk of heart and lung disease carry surface-absorbed carcinogenic compounds into the lungs smaller particle fraction PM2.5 capable of penetrating deepest into the lungs
8. Ozone (O 3 ) ~a secondary pollutant produced by reaction between nitrogen dioxide (NO 2 ), hydrocarbons and sunlight ~is photodissociated itself (split up by sunlight) to form free radicals ~ promotes the oxidation chemistry ~catalyses its own formation (i.e.. it is an autocatalyst) ~ powerful oxidizing agent
Effect persist for several days and be transported over long distances. irritate the eyes air passages causing breathing difficulties increase susceptibility to infection is a highly reactive chemical, capable of attacking surfaces, fabrics and rubber materials toxic to some crops, vegetation and trees.
9. Benzene Benzene ~ is an aromatic VOC. ~ is a minor constituent of petrol ( about 2% by volume) Main sources : refining, distribution and combustion of petrol Effect : human carcinogenic
10. 1,3-butadiene 1,3-butadiene ~ is a VOC emitted into the atmosphere from fuel combustion of petrol and diesel vehicles. ~ is produced by the combustion of olefins. ~ is an important chemical in certain industrial processes, particularly the manufacture of synthetic rubber. Effect: potent, human carcinogenic
11. TOMPs (Toxic Organic Micropollutants) ~ produced by the incomplete combustion of fuels ~ comprise a complex range of chemicals Compounds in this category include: PAHs (PolyAromatic Hydrocarbons) PCBs (PolyChlorinated Biphenyls) Dioxins Furans Effect: carcinogenic.
Ozone depletion The greenhouse effect Acid rain
The "ozone layer" is a region of relatively high ozone concentration (at about 25 km altitude) in the stratosphere, which is a layer of the atmosphere between 15 and 50 km
1.Chlorofluorocarbons (CFCs) stable, nonflammable, low in toxicity, inexpensive to produce uses as refrigerants, solvents, foam blowing agents,etc. 2.Chlorine-containing compounds e.g. methyl chloroform(solvent) carbon tetrachloride( an industrial chemical) 3.Halons effective fire extinguishing agents 4.Methyl bromide effective produce and soil fumigant All of these compounds have long atmospheric lifetimes transported by winds into the stratosphere release chlorine or bromine when break down damage the protective ozone layer
»» strong UV radiation breaks down CFC »» CFC molecule releases atomic chlorine »» one chlorine atom can destroy over 100,000 ozone molecules
Example of ozone depletion ~ the annual ozone "hole" over Antarctica ozone levels levels of UVB reaching the Earth's surface Effect: UVB causes nonmelanoma skin cancer and plays a major role in malignant melanoma development. UVB harms some crops, plastics and other materials, and certain types of marine life. Formation and destruction of ozone Sunlight - major energy source for both making and destroying stratospheric ozone Up to 98% of the sun's high-energy ultraviolet light(UV-B and UV-C) are absorbed by the destruction and formation of atmospheric ozone
Halogen catalysis of ozone degredation Halogens ~ a chemical family containing fluorine, chlorine, bromine and iodine ~ catalyze ozone breakdown Halocarbon ~ carbon compound containing halogens NO, NO 2 and OH radicles ~ catalysts in ozone degredation in the troposphere and lower stratosphere
The greenhouse effect
Cause Excessive production of CO2 Reason Burning a great amount of fossil fuel forests are cleared in a great rate Process Energy from the sun falls on the earth and warms it up the earth radiates some of the heat energy back to the space CO2 absorbs some of the heat energy and prevents it escaping from the earth atmosphere the temperature of earth increase
Effect Tones of polar ice melts and flow into the oceans. The level of the oceans would rise. Low-lying areas of land would be flooded cause severe drought in some countries
Methods to reduce the greenhouse effect Stop cutting down forests start new plantation stop to use or use less fossil fuel use alternative energy source such as solar energy
Acid deposition Cause : emissions of sulphur dioxide and nitrogen oxides Source: use of coal in the production of electricity base-metal smelting fuel combustion in vehicles
Formation of Acids in the Atmosphere Converting NO x and SO2 to Acids SO 2 : Gas Phase SO 2 (g)+H 2 O(l) H 2 SO 3 (aq) sulphurous acid 2SO 2 (g)+O 2 (g)+2H 2 O(l) 2H 2 SO 4 (aq) sulphuric acid Aqueous Phase [S(IV)] [SO 2 (aq)] + [HSO 3 - ] + [SO 3 2- ] This dissociation occurs by a two-fold process: 1) SO 2 (aq) H + + HSO 3 - 2) HSO 3 - (aq) H + + SO 3 2-
NOx: Gas Phase 2NO 2 (g)+H 2 O(l) HNO 2 (aq)+HNO 3 (aq) nitrous acid and nitric acid Aqueous Phase 1. 2NO 2 (g) + H 2 O(l) 2H + + NO NO NO(g) + NO 2 (g) + H 2 O(l) 2H + + 2NO NO 2 (g) + H 2 O(l) 2H + + 2NO NO(g)
ACID RAIN - A DEFINITION pH of rainwater < 5.5 pH of normal rainwater = 5.5 to 5.7
EFFECT ON ARCHITECTURE - damage to limestone or marble CaCO+2H + H 2 O +CO 2 EFFECT ON TREES AND SOILS - damage the plants, change the pH of soil EFFECT ON METALWORK - increase the corrosion rate of metals
EFFECT ON LAKES AND AQUATIC ECOSYSTEMS pH LEVEL <6 *Basic forms of food die off. e.g. Mayflies and stoneflies are important food sources for fish. They can't survive. <5.5 *Fish cannot reproduce. *Young have difficulty staying alive. *More deformed adult fish due to lack of nutrients *Fish die of suffocation <5.0 *Fish population die off. <4.0 *Very different lifeforms
Reducing SO2 Emissions Before Combustion 1. Coal Cleaning removing pyritic sulfur (FeS2) 2. Burning of Low Sulfur Coals (Subbituminous coal is of lower sulfur content than bituminous coal.) During Combustion 1. FBC - Fluidized Bed Combustion
After Combustion 1. Wet Flue Gas Desulfurization - The wet scrubber consists of either limestone, lime, or sodium hydroxide. CaCO 3 + SO 2 + H 2 O + O 2 CaSO 3 + CaSO 4 + CO 2 + H 2 O 2. Dry Scrubbing - The process of dry scrubbing involves the contact between drying gas and the atomized liquid (alkaline based)
Reducing NOx Emissions During Combustion - Overfire Air After Combustion The catalytic reduction system - involves the injection of ammonia gas upstream of the catalytic reaction chamber 4NO + 4NH 3 + O 2 4N 2 + 6H 2 O 2NO 2 + 4NH 3 + O 2 3N 2 + 6H 2 O nitrogen gas is harmless
Eutrophication and algal blooms Phosphorus is the nutrient controlling the size of freshwater blue-green algal blooms Amount of bio-available phosphorus (orthophosphate) algal blooms
A sewage treatment plant discharge An irrigation return drain in the lower reaches, and an upland tributary, draining a semi-agricultural catchment
Diagram of the interactions (sedimentation / re- suspension, uptake / release) between different components of the aquatic environment and orthophosphate. Certain algal species release toxins that cause massive fish kills. Thousands of tons of dead fish litter beaches, bays, and estuaries during these red tide blooms.
EFFECT loss of fish and shellfish Human health - eating clams, mussels, oysters or scallops contaminated by red tide can cause severe illness and even death to humans. Aerosols from red tides can produce respiratory ailments long-term consequences of inhaling potent neurotoxins from algae release harmful toxins causing mass mortalities of various marine organisms
Organic pollution Human sewage, refuse, agricultural waste like manure of chicken and pigs and certain industrial wastes which contain large amount of organic matter 1. Self-purification of water: The water is well aerated when the amount of organic pollutants is small. They are rapidly decomposed by bacteria and fungi into simple inorganic compound. If the amount of organic pollutants is very heavy, it will remove all the dissolved oxygen and self -purification of water. In the absence of oxygen the incomplete decomposition of organic matter by anaerobic bacteria produces many unpleasant smelling gases such as methane, ammonia and hydrogen sulphides.
Red tides are caused by the explosive population growth of a minute, single-celled group of algae called dinoflagellates Hong Kong Red Tide (Unidentified species)
Oil Millions tones of oil leak out from oil tankers. Affects: - oil floats on water. The oil layer prevent oxygen dissolving in the water. - birds lose warmth quickly when there are covered with oil
Soapy detergents(Soap) - an anionic surfactant - sodium salt or potassium salt of long chain alkanoic acids - COO - group - from animal fats and vegetable oils Soapless detergents(synthetic detergents/detergents) - sodium salt salt of organic acids with a very long hydrocarbon chain - SO3 - or SO4 - group
Common soap (hard soap) e.g. sodium stearate CH 3 -(CH 2 ) 16 -COO - Na + Soft soap &liquid soap e.g. potassium stearate CH 3 -(CH 2 ) 16 -COO - K + sodium lauryl sulphate in shampoo (soapless detergent) CH 3 -(CH 2 ) 11 -O-SO 3 - Na + sodium lauryl benzenesulphonate(an alkylbenzenesulphonate) (soapless detergent) in washing powder & liquid detergent CH 3 -(CH 2 ) 11 -C 6 H 4 - SO 3 - Na +
AFFECT OF SOAP 1.Forms insoluble scum with Ca 2+ &Mg 2+ of hard water 2CH 3 (CH 2 ) 16 COO - (ag) (CH 3 (CH 2 ) 16 COO - ) 2 Ca 2+ (s) 2.forms insoluble long chain alkanoic acid 2CH 3 (CH 2 ) 16 COO - (ag) CH 3 (CH 2 ) 16 COOH(s)
Affect of soapless detergent Health problems- cause skin allergies e.g.pH > 9 or < 5 Branched hydrophobic chain are non-biodegradable Ecological disturbance -formation of foams in rivers -prevent the breathing of aquatic lives kills aquatic lives Phosphate additives(water softener) speed up the growth of algae
Chemical pollution Pesticides - poisonous chemicals deliberately sprayed to kill a particular organism (e.g. herbicides, fungicides and insecticides) Thermal pollution High temperature - will raise the metabolic rate and oxygen consumption of aquatic organisms - decrease the oxygen solubility in water and the resulting deoxygenation may seriously affect the aquatic organisms.