AIR POLLUTION

OBJECTIVES Ability to define air pollution Ability to describe classification of pollutant and particulate. Ability to describe the effect of pollutant to health, plants and material. Ability to explain stability of atmosphere including plume types. Air quality control and treatment of emission products

DEFINITION Air pollution is the presence in the outdoor atmosphere of one or more air contaminants (i.e., dust, fumes, gas, mist, odour, smoke, or vapour) in sufficient quantities, of such characteristics, and of such duration as to be or to threaten to be injurious to human, plant, or animal life or to property, or which reasonably interferes with the comfortable enjoyment of life or property’

CLSSIFICATION OF POLLUTANT Pollutant can be classified into THREE that are: 1) Origin Primary pollutants – such as SOx, NOx and hydrocarbon (HC) are those emitted directly to the atmosphere and were found in the form in which they were emitted. Secondary Pollutants – such as O3 and peroxyacethyl nitrate (PAN) are those formed in the atmosphere as the result of chemical reactions among the primary pollutant and chemical species present in the atmosphere.

2) Chemical Composition Organic compounds – contain carbon & hydrogen, and may also contain element such as O, N , P and S. Inorganic compounds – found in contaminated atmosphere include CO, CO2, carbonates, SOx, NOx,O3, HCl.

3) State of Matter Particulate pollutants – finely divided solids and liquids, include dust, fumes, smoke, fly ash, mist and spray.Under proper properties, particulate pollutant will settle. Gaseous pollutants – formless fluids that completely occupy the space into which they are released, behave more as air & do not settle down. Including vapors of substance that are liquid or solid at normal Pressure & T. e.g: COx, SOx, NOx, HC and oxidants.

PARTICULATES Particles can be classified from their mode of formation as dust, smoke, fumes, fly ash, mist, or spray. The sizes range from 1000 µm – 0.01 µm. The particles sizes from 100 µm – 0.01 µm are the major interest in air pollution studies because within these sizes the particulates can easily settle in lower respiratory tract (LRT).

small, solid particles created by the breakup of larger masses through processes such as crushing, grinding or blasting, may come directly from the processing or handling of materials such as coal, cement or grains. The size range from 1.0 µm to 1 000 µm. Dust fine, solid particles resulting from the incomplete combustion of organic particles such as coal, wood or tobacco consists mainly of carbon and other combustible materials. The size range from 0.5 µm to 1 µm. Smoke fine, solid particles (often metallic oxides such as zinc and lead oxides) formed by the condensation of vapors of solid materials. Fumes are from sublimation, distillation, calcination or molten metal processes. The size range from 0.03 µm to 0.3 µm. Fumes

finely divided solid particle, noncombustible particles contained in flue gases arising from combustion of coal and it is released when the organic portion of coal is burned. The size range from 1.0 µm to 1000 µm. Fly ash Mist liquid particles or droplet formed by condensation of vapor, dispersion of a liquid (e.g. in foaming & splashing) or enactment of chemical reaction (e.g. formation of H2SO4). The sizes of mist <10 µm. Spray liquid particles formed by atomization of parent liquids (e.g. pesticides & herbicides). The size range from 10 µm to 1000 µm.

Air Quality Measurements Particulates Measurments Mini Volume Portable Sampler High Volume Sampler

Air Quality Measurements The filter is weighted before and after and the difference is the particulates collected the air flow is measured by a small flow meter, usually calibrated every 24 hours because its get dirty during 24 hours of operations. Less air goes through the filter during later part of the test than the beginning. Therefore air flow has to measure at both points , starting and ending points. since the later part has different air flow than the beginning, air flow value it’s the average value of the start and end of the test.

Air Quality Measurements Ex1: A clean filter is found to weigh 10 grams. After 24 hours in hi-vol , the filter plus dust weighs 10.1 grams. The air glow at the start and end of the test are 60 & 40 m3/min respectively. What is the dust particulate concentration?

Air Quality Measurements Gaseous measurements The concentration of gasses can be either part per million (ppm) on a volume to volume basis or micrograms per cubic meter. ppm means 1 volume of pollutants per 106 volume of Air. Converting µg/m3 needs to know the molecular weigh of the gas. At standard condition 00C and 1 Atmosphere pressure, one mole of gas occupies 22.4 L while at 250C and 1 Atmosphere pressure, one mole of gas occupies 24.5 L

Air Quality Measurements Ex 2: A stack gas contains carbon monoxide (CO) as a concentration of 10% by volume. What is the concentration of (CO) in microgram per cubic meter. If CO MW is 28 g/mol, assume 250C and 1 Atmosphere pressure.

UNITS OF MEASUREMENT There are 3 basic units used in reporting air pollution data that are micrograms per cubic meter (µg/m3), parts per million (ppm) and the micron (µ) or preferably known as micrometer (µm). Micrograms per cubic meter and parts per million are unit of measurement for concentration and they are used to indicate the concentration of gaseous pollutant. The µm is used to report the particle size. Formerly concentration of gaseous pollutants were usually reported in parts per million (ppm), parts per hundred million (pphm), or parts per billion (ppb) by volume. Thus, designations in µg/m3 may be followed by equivalent concentration on a ppm basis - e.g. 80 µg/m3 (0.03 ppm) of sulfur dioxide.

µg/m3 = ppmx 10-6 xGMW x103 L/m3 x106 µg/g L/mol For gases, ppm can be converted to µg/m3 by using the following formula: µg/m3 = ppmx 10-6 xGMW x103 L/m3 x106 µg/g L/mol GMW = gram molecular weight of gas ‘L/mol’ term is influenced by the temperature (T) and pressure (P) of the gas. According to Avogadro’s Law, 1 mole of any gas occupies the same volume as 1 mole of any gas at the same T and P. Therefore, at 273 K (0OC) and 1 atm pressure (760 mmHg /101.3 kPa), standard conditions for many chemical reactions, the volume is 22.4 L/mol.

To convert to L/mol at other conditions, the following formula can be used: V1P1 = V2P2 T1 T2 where V1, P1 and T1 is relate to the standard condition V2, P2 and T2 is relate to the actual condition that is being considered.

EXAMPLE : Calculate the volume occupied by 4 mol of gas at 21.1OC and 760 mmHg. SOLUTION:

DO IT YOURSELF Determine the volume of 3 mol of stack gas at 1400 mmHg and 1000OC.

EXAMPLE : The NO2 content of a sample of stack gas measured at 950OC at 2 atm pressure was 9 ppm. Determine the NO2 concentration in µg/m3 and mg/m3. NO2 weight 46 g/mol. SOLUTION:

DO IT YOURSELF Gas from thermal pool has an SO2 content of 80 µg/m3 at 104.2 kPa and 50OC. Calculate the SO2 concentration in ppm.

EXAMPLE : What volume would one mole of an ideal gas occupy at 25.00C and 101.325kPa?. SOLUTION:

Determine the volume of 6 mol of gas at 370C and 700 mmHg. EXAMPLE : Determine the volume of 6 mol of gas at 370C and 700 mmHg. SOLUTION:

Convert 7.5 ppm of 64 g/mol SO2 to µg/m3 at 80OC and 110.5 kPa. EXAMPLE : Convert 7.5 ppm of 64 g/mol SO2 to µg/m3 at 80OC and 110.5 kPa. SOLUTION:

Effects of Acidic Rain -The potential effects of acid rain are relates to the acidity on aquatic life, damage to crops and forests, and damage to building materials. -Lower pH values may affect fish directly by interfering with reproductive cycles or by releasing otherwise insoluble aluminium (Al), which is toxic. Acid rain also leaches calcium (Ca) and magnesium (Mg) from the soil thus lower the molar ratio of Ca to Al which in turn, favours the uptake of Al by fine roots, that ultimately leads to their deterioration.

AIR Quality Control Treatment of Emissions

AIR Quality Control Selection of treatment devices will be depend on : 1- size of Air pollutant 2- Type of Air pollutant, such as SO2 can clean by water spray but the result is corrosion problem. Therefore, are divided into different types for Air pollutant control process.

AIR Quality Control Where: Xo X1 X2 Where: Xo : Amount of pollutant entering the device per unit time (kg/s) X1 : Amount of pollutant collected by treatment device per unit time (kg/s) X2 : Escaped particles (kg/s)

AIR Quality Control Where: R: Treatment device removal efficiency Concentration of emission will be equal to the mass per volume. Principles of mass balance will be valid for this process

AIR Quality Control EX: An air pollution control device is to remove a particulate that is being emitted at a concentration of 125000 µg/m3 at an air flow rate of 180 m3/s. the device removes 0.48 ton per day. What are the emission concentration and the collection recovery?

AIR Quality Control Cyclone Collector Cyclones provide a low cost, low maintenance method of removing larger particulates from a gas stream. Mechanism 1- The particulate is forced to change direction. 2- The particles continue in the original direction and be separated from the stream. 3- The walls of the cyclone narrow towards the bottom of the unit allowing the particles to be collected in a hopper. 4- The cleaner air leaves the cyclone through the top of the chamber.

AIR Quality Control Cyclone are efficient in removing large particles but are not sufficient with smaller particles. For this reason, they are used with other particulate control devices. Proper disposal for the collected material is needed. why? Collected solid particles are most often disposed off in a landfill.

Settling chamber Used to remove the large particle fraction from gas streams. Collection in settling chamber depends on the settling velocity of the particles being removed. Particles with diameters greater than 50µm to 100 are effectively removed

EX: Assume a point source particulate emission having an effective stack height of 61 m. the plume contains particles having a density of 2.3 g/cm3 , the stack gas temperature is 800 F, and the wind speed is constant at 5 mph. Assuming the terrain is flat. Calculate the distance downward that a 5,10, and 100 µm particle will travel.

Settling chamber Design Settling chambers are typically designed having a velocity less than 3 m/s, best results being obtained with velocities less than 0.3 m/s. For a particle that enters the top of the collector and is removed, the time for the particle to fall the collector height H must be less than or equal to the time of the horizontal movement within the collector such that:

Time for the particle to fall H distance = time of horizontal movement Where : L: is the length of the hopper V: is the horizontal flow through the velocity

Reducing H/L ratio will result in removing smaller particles Reducing H/L ratio will result in removing smaller particles. For particle size below that predicted by above equation, the removal efficiency for laminar flow situations is:

EX: Design a settling chamber to collect particles 50 µm in diameter and 2000 Kg/m3 in density from an air stream with a volumetric flow of 1.5 m3 /s. the chamber is to be 2.0 m in width and 2.0 m in height. How long must the chamber be to give theoretical perfect collection efficiency? Determine the collection efficacy for particles of the same density that are 25 µm in diameter.