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Chapter 2

Chapter 2. Sources, Types & Distribution of Air Pollution. Major Sources of Air Pollution. The number of different types of pollution sources in modern society is almost endless. We look at only the most significant sources of air pollutants. Mobile (50 - 70%), and stationary sources.

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Chapter 2

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  1. Chapter 2 Sources, Types & Distribution of Air Pollution

  2. Major Sources of Air Pollution • The number of different types of pollution sources in modern society is almost endless. • We look at only the most significant sources of air pollutants. • Mobile (50 - 70%), and stationary sources. • 15-25% from heavy industrial stationary sources and as much as 25% from other stationary sources.

  3. Major Sources of Air Pollution

  4. Major Sources of Air Pollution • The table is from USA. The total amount emitted in Australia will be far less • A significant reduction in the amounts of CO and H/C’s when compared to the previous decade • levels of other pollutants has been steady or shown only a slight increase

  5. Transportation Combustion Sources • The most important transportation sources at present are major polluters • Motor vehicles CO, CO2 H/C’s, NOx and small amounts of SOx • Motor vehicle exhaust accounts for 40% of all H/C air pollutants and 90% of all NO2

  6. Transportation Combustion Sources • Motor vehicles pollutants react to form more reactive (and dangerous) pollutants such as photochemical smog. • diesel fuel = a source of very dangerous H/C’s (PAH’s). • Pb has decreased in significance, and according to the latest national SoE report, is no longer considered a problem • vehicles running on unleaded fuels emit lower levels of NOx and SOx

  7. Transportation Combustion Sources • Aircraft and trains are less significant sources of pollution compared with road transport vehicles. • Aircraft run on kerosene, burnt efficiently, but they fly very high in the atmosphere the pollutants – most of which are H/C’s – are spread and diluted in the upper atmosphere. DISCUSS NEW PROBLEM • Trains mostly run on electricity = contribute very little to air pollution (except CO2 & some ozone)

  8. Stationary Combustion Sources • Some of the more important sources include • furnaces - and their combustion of carbonaceous fuels • boilers • ovens and dryers • process systems which produce volatile chemicals, gases, etc.

  9. Stationary Combustion Sources • Solvent evaporation (fugitive) from; • solvent-based materials • leaking pipe joints • maintenance work • spills, unloading /loading procedures • an important part of photochemical pollution

  10. Stack Emissions • Emission of waste gases, fumes, vapours and smokes to the atmosphere are usually by the use of a smoke stack or chimney. • stack emission becomes a plume in the atmosphere. • The plume is an area of concentrated waste emissions that slowly become diluted with the other atmospheric gases.

  11. Stack Emissions How dilution happens depends on many factors • Nature of the waste emission • Toxic emissions need to be very dilute • Volume of the waste • Is emission constant or only at certain times in the process. • Local topography • Many cities located in areas surrounded by hills or mountains. • low wind and cooler temperatures = photochemical smog.

  12. Stack Emissions • Prevailing climate • direction of prevailing winds • e.g. Queenstown, Tasmania • The Existing Atmosphere • In very polluted cities, more stack emissions not desirable. • e.g. build power stations in the country away from NOx from cars

  13. Plume Behaviour • Effects of plumes are considered local within 500 metres of the stack, and regional beyond this. • Mixing or dispersion of the waste gases and products into the atmosphere = plume behaviour.

  14. Types of Plumes • Fanning plumes • Looping plumes • Coning plumes • Fumigating • Lofting

  15. The Fanning Plume • Fanning Plumes • Require stable air and slow vertical movement of the emission • common after calm clear nights • temperature inversion limits the rise of the plume into the upper atmosphere

  16. The Fanning Plume • creates a higher conc. of polluted air at lower levels • exists for several hours • Commonly seen from Eraring Power station

  17. Looping plumes • Looping plumes • Require windy conditions which cause the plume can swirl up and down • common in the afternoon. • Moderate and strong winds are formed on sunny days creating unstable conditions • Exists for several hours.

  18. Coning plumes • Coning plumes • Require moderate winds and overcast days • wider than it is deep, and is elliptical in shape • exists for several hours.

  19. Fumigating plume • Fumigating plume • Is short-lived (fraction of an hour), but reaches the earth's surface. • occur when the conditions move from stable to unstable • A fanning plume develops overnight under stable conditions but as the day heats up, unstable air is produced

  20. Fumigating Plume • Fumigating plume (cont) • unstable air causes the plume to move up and down - can cause localised pollution. • become looping or coning plumes as the air conditions stabilise.

  21. Lofting plume • Lofting plume • When plume is above the inversion layer (or there is no inversion), it becomes a lofting plume. • Normal wind direction and speed will disperse the plume into the atmosphere without effect from ground warming or cooling.

  22. Stack emissions • factors used to establish the amount of stack emission allowed, and its conc. to the atmosphere include: • smoke stack (chimney) height, • local topography, • temperature, • emission rates, • chemical reactivity, and • existing air pollution problems • wind allow rapid dispersal of pollutants.

  23. Fugitive Emissions • Fugitive emissions are emissions which escape from a process rather than being discharged • They often have serious consequences because their levels are not monitored and they are untreated when entering the atmosphere

  24. Fugitive Emissions • There are many sources of fugitive emissions including: • industrial sources (particulate fluorides from aluminium smelters) • small business (e.g. dry cleaning solvents) • agriculture (e.g. dust from ploughing) • natural sources (e.g. volcanoes, forest fires)

  25. Fugitive emissions • Often the result of poor maintenance of plant and equipment • Can be eliminated by SOP’s that involve timed maintenance and quality control checks • Some are almost impossible to control (e.g. natural sources)

  26. Types of air pollutants • There are four types of air pollutants; • particulate pollutants and • gaseous pollutants, • odour and • noise.

  27. Primary vs Secondary pollutants • Not all of the pollutants found in the atmosphere are the direct result of emissions. • Many pollutants arise from chemical reactions in the atmosphere with other substances or light (photochemical reactions).

  28. 1° vs 2° pollutants • Pollutant substances that are directly emitted into the atmosphere = primary pollutants. • Substances not directly emitted into the atmosphere, formed by chemical reactions in the atmosphere = secondary pollutants.

  29. Particulate Pollutants • Very small solid or liquid particles • Individual particles may vary in size, geometry, chemical composition and physical properties • May be of natural origin (pollen or sea spray) or man made (dust, fume and soot)

  30. Particulate Pollutants • Provide a reactive surface for gases and vapours in the formation of secondary pollutants • Particles also diffuse light reducing visibility • Come from stack emissions, dusty processes, unsealed roads, construction work and many other sources

  31. Particulate Pollutants • Dusts • large solid particles • Fume • solid particles (metallic oxides) formed by condensation of vapours from a chemical reaction process or physical separation process

  32. Particulate Pollutants • Mist • liquid particles formed by condensation of vapours or chemical reaction. SO3 + H2O H2SO4 • Smoke • solid particles formed as a result of incomplete combustion of carbonaceous materials. • Spray • a liquid particle formed by the atomisation of a parent liquid.

  33. Particle Size • Particles range in size from 0.005 - 500m. • Smallest of these are clusters of molecules whilst the largest are easily visible with the naked eye. • Sizes given are not the physical size, but rather the aerodynamic equivalent diameter which relates the particle to the behaviour of an equivalent spherical particle.

  34. Particle Size • Particles less than 1m in diameter behave like gases (remain suspended, may coalesce, move in fluid streams), • Larger particles act like solids (affected by gravity, don’t stay suspended long, don’t coalesce). • Smaller particles generally derive from chemical reactions, whereas the larger particles (10m or greater) are usually generated mechanically and tend to be basic.

  35. Particle Size • Smaller particles most dangerous to health, • In urban areas there is an approx. even distribution between fine and coarse particles, this is weather dependent. • Calm conditions more fine particles than coarse, • Fine particulate matter spread over much greater distances

  36. Particle behaviour in the atmosphere • Particles can undergo many physical and chemical changes; • grow in size, • absorb or desorb gases from their surfaces, • change electrical charge,

  37. Particle behaviour in the atmosphere • Particles can undergo many physical and chemical changes; • collide or adhere with other particles, • absorb water. • changes the particle size and affect its atmospheric lifetime.

  38. Total Suspended Particles (TSP) • Most particles concentrated into three main size groups • Larger particles around 10m in size • Smaller particles in size groups centred around 0.2 and 0.02m.

  39. TSP • Only particles of <10m penetrate into the human lung • Analyse air for only this fraction to estimate its potential danger to human health = PM10 sampling. • Particles <2.5m in size can penetrate deep into the lung tissue and are especially dangerous = PM2.5 sampling

  40. Organic Particulates • PAH most significant • Found on soot and dust particles, and are formed from smaller H/C’s at high temperatures (coal furnace effluent may contain 1mg/m3 of PAH cigarette smoke 0.1mg/m3) • Urban atmospheres PAH levels ~20 ug/m3 but is highly variable

  41. Lead Particulates • Was the most serious atmospheric heavy-metal pollutant, but is no longer • primary source was exhaust from vehicles

  42. Gaseous Pollutants • CO, H/C’s, H2S, NOx, O3 and other oxidants, and SOx • Measured in micrograms per cubic meter (ug/m3) or parts per million (ppm). • 1 ppm = 1 volume of gaseous pollutant • 106 volumes of (pollutant + air)

  43. Gaseous Particulates • At 25°C and 101.3 kPa the relationship between ppm and ug/m3 is; ug/m3 = ppm x molecular weight x 103 24.5

  44. Carbon Monoxide • a colourless, odourless and tasteless gas. • atmosphere has an avg. burden of around 530 million tonnes (about 0.00001%), • avg. residence time of 36 to 100 days. • Much of the CO in the atmosphere occurs naturally from volcanic eruptions, photolysis of methane and terpenes, decomposition of chlorophyll, forest fires and microbial action in oceans.

  45. Carbon Monoxide • Anthropogenic sources = transportation, solid waste disposal, agricultural burning, steel production, etc. • emitted directly into the atmosphere through the inefficient combustion of fossil fuels. • removed by reactions in the atmosphere which change it to CO2 and by absorption by plants and soil micro-organisms.

  46. Carbon Monoxide • It is removed by reactions in the atmosphere which change it to CO2 and by absorption by plants and soil micro-organisms. • In combustion, carbon is oxidised to CO2 in a two step process. 2C + O2 2CO 2CO + O2 2CO2

  47. Carbon Monoxide • Typical conc's • Background levels of CO tend to vary greatly depending on location. • avg. global levels = 0.2ppm. • Peak conc's during autumn months when large volumes are generated by the decomposition of chlorophyll in leaves. • In urban areas = diurnal conc. pattern

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