Air Pollution AIR POLLUTION PRESENCE OF ANY SUBSTANCES
Air Pollution
AIR POLLUTION PRESENCE OF ANY SUBSTANCES, SOLID, LIQUID OR GAS IN THE ATMOSHPHERE IN SUCH A CONCENTRATION, THAT MAY OR MAY NOT TENDS TO INJURIOUS TO HUMANS, ANIMALS, PLANTS, PROPERTIES OR THE ATMOSHPERE ITSELF, IS REFFERED TO AS AIR POLLUTION AND THE SUBSTANCE AIR AS AIR POLLUTANTS.
CLEAN ATM + EXTERNAL ADDITION =EFFECTS
Human Health Effects • Exposure to air pollution is associated with numerous effects on human health, including pulmonary, cardiac, vascular, and neurological impairments. • The health effects vary greatly from person to person. High-risk groups such as the elderly, infants, pregnant women, and sufferers from chronic heart and lung diseases are more susceptible to air pollution. • Children are at greater risk because they are generally more active outdoors and their lungs are still developing.
Conti…. . • Exposure to air pollution cause both acute (short -term) and chronic (long-term) health effects. • Acute effects are usually immediate and often reversible when exposure to the pollutant ends. Some acute health effects include eye irritation, headaches, and nausea. • Chronic effects are usually not immediate and tend not to be reversible when exposure to the pollutant ends. – Some chronic health effects include decreased lung capacity and lung cancer resulting from longterm exposure to toxic air pollutants.
Effects on Human respiratory system • Both gaseous and particulate air pollutants can have negative effects on the lungs. • Solid particles can settle on the walls of the trachea, bronchi, and bronchioles. • Continuous breathing of polluted air can slow the normal cleansing action of the lungs and result in more particles reaching the lower portions of the lung. • Damage to the lungs from air pollution can inhibit this process and contribute to the occurrence of respiratory diseases such as bronchitis, emphysema, and cancer.
Table 1: Sources, Health and Welfare Effects for Criteria Pollutants. Pollutant Description Sources Health Effects Welfare Effects Carbon Monoxide (CO) Colorless, odorless gas Motor vehicle exhaust, indoor sources include kerosene or wood burning stoves. Headaches, reduced mental alertness, heart attack, cardiovascular diseases, impaired fetal development, death. Contribute to the formation of smog. Sulfur Dioxide (SO 2) Colorless gas that dissolves in water vapor to form acid, and interact with other gases and particles in the air. Coal-fired power plants, petroleum refineries, manufacture of sulfuric acid and smelting of ores containing sulfur. Eye irritation, wheezing, chest tightness, shortness of breath, lung damage. Contribute to the formation of acid rain, visibility impairment, plant and water damage, aesthetic damage. Nitrogen Dioxide (NO 2) Reddish brown, highly reactive gas. Motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. Susceptibility to respiratory infections, irritation of the lung and respiratory symptoms (e. g. , cough, chest pain, difficulty breathing). Contribute to the formation of smog, acid rain, water quality deterioration, global warming, and visibility impairment. Ozone (O 3) Gaseous pollutant when it is formed in the troposphere. Vehicle exhaust and certain other fumes. Formed from other air pollutants in the presence of sunlight. Eye and throat irritation, coughing, respiratory tract problems, asthma, lung damage. Plant and ecosystem damage. Lead (Pb) Metallic element Metal refineries, lead smelters, battery manufacturers, iron and steel producers. Anemia, high blood pressure, brain and kidney damage, neurological disorders, cancer, lowered IQ. Affects animals and plants, affects aquatic ecosystems. Particulate Matter (PM) Very small particles of soot, dust, or other matter, including tiny droplets of liquids. Diesel engines, power plants, industries, windblown dust, wood stoves. Eye irritation, asthma, bronchitis, lung damage, cancer, heavy metal poisoning, cardiovascular effects. Visibility impairment, atmospheric deposition, aesthetic damage.
Table-2: Sources, Effects of Air Pollutants on Vegetables Pollutants Sources Effects on Vegetables Aldehydes Photochemical reactions The upper portions of Alfalfa etc. will be affected to Narcosis if 250 ppm of aldehydes is present for 2 hrs duration. Ozone (O 3) Photochemical reaction of hydrocarbon and nitrogen oxides from fuel combustion, refuse burning, and evaporation from petroleum products. All ages of tobacco leaves, beans, grapes, pine, pumpkins and potato are affected. Fleck, stipple, bleaching, bleached spotting, pigmentation, growth suppression, and early abscission are the effects. Peroxy Acetyl Nitrate (PAN) The sources of PAN are the same as ozone Young spongy cells of plants are affected if 0. 01 ppm of PAN is present in the ambient air for more than 6 hrs. Nitrogen dioxide (NO 2) High temperature combustion of coal, oil, gas, and gasoline in power plants and internal combustion engines. Irregular, white or brown collapsed lesion on intercostals tissue and near leaf margin. Suppressed growth is observed in many plants. Ammonia & Sulfur dioxide Thermal power plants, oil and petroleum refineries. Bleached spots, bleached areas between veins, bleached margins, chlorosis, growth suppression, early abscission, and reduction in yield and tissue collapse occur. Chlorine (Cl 2) Leaks in chlorine storage tanks, hydrochloric acid mists. If 0. 10 ppm is present for at least 2 hrs, the epidermis and mesophyll of plants will be affected. Hydrogen fluoride, Silicon tetrafluoride Phosphate rock processing, aluminum industry, and ceramic works and fiberglass manufacturing. Epidermis and mesophyll of grapes, large seed fruits, pines and fluorosis in animals occur if 0. 001 ppm of HF is present for 5 weeks. Pesticides & Herbicides Agricultural operations Defoliation, dwarfing, curling, twisting, growth reduction and killing of plants may occur. Particulates Cement industries, thermal power plants, blasting, crushing and processing industries. Affects quality of plants, reduces vigor & hardness and interferences with photosynthesis due to plugging leaf stomata and blocking of light. Mercury (Hg) Processing of mercury containing ores, burning of coal and oil. Greenhouse crops, and floral parts of all vegetations are affected; abscission and growth reduction occur in most of the plants.
PEOPLE PERSONAL EXPOSURE SMOKERS CHILDREN PERSONAL CAR AMBIENT LEVELS NON SMOKERS COMMUTER PUBLIC TRANSPORT CONTROL INDOOR ENVIRONMENTS HOMES WALK OR CYCLING BUS OUTDOOR ENVIRONMENTS OTHER LOCATIONS SCHOOLS CITY BACKGROUND OFFICES AND SHOPS HOT SPOTS BARS TRAM METRO Support from citizens Support from local authorities
HAPS [http: //www. epa. gov/ttnatw 01/orig 189. html] • CLEAN AIR ACT AMENDMENTS OF 1990 DIRECTED EPA [Environmental Protection Agency] TO ESTABLISH EMISSION CONTROLS FOR 189 CHEMICALS LISTED IN THE ACT. • ACT NOT BASED ON HEALTH CRITERIA BUT BASED ON MAXIMUM ACHIEVABLE CONTROL TECHNOLOGY[MACT]
What are toxic air pollutants? [http: //www. epa. gov/air/toxicair/newtoxics. html] • Toxic air pollutants, also known as hazardous air pollutants, are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. EPA is working with state, local, and tribal governments to reduce air toxics releases of 187 pollutants to the environment. Examples of toxic air pollutants include benzene, which is found in gasoline; perchloroethylene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper by a number of industries. Examples of other listed air toxics include dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds.
What are the health and environmental effects of toxic air pollutants? • People exposed to toxic air pollutants at sufficient concentrations and durations may have an increased chance of getting cancer or experiencing other serious health effects. These health effects can include damage to the immune system, as well as neurological, reproductive (e. g. , reduced fertility), developmental, respiratory and other health problems. In addition to exposure from breathing air toxics, some toxic air pollutants such as mercury can deposit onto soils or surface waters, where they are taken up by plants and ingested by animals and are eventually magnified up through the food chain. Like humans, animals may experience health problems if exposed to sufficient quantities of air toxics over time.
Where do toxic air pollutants come from? • Most air toxics originate from human-made sources, including mobile sources (e. g. , cars, trucks, buses) and stationary sources (e. g. , factories, refineries, power plants), as well as indoor sources (e. g. , some building materials and cleaning solvents). Some air toxics are also released from natural sources such as volcanic eruptions and forest fires.
How are people exposed to air toxics? • • People are exposed to toxic air pollutants in many ways that can pose health risks, such as by: Breathing contaminated air. Eating contaminated food products, such as fish from contaminated waters; meat, milk, or eggs from animals that fed on contaminated plants; and fruits and vegetables grown in contaminated soil on which air toxics have been deposited. Drinking water contaminated by toxic air pollutants. Ingesting contaminated soil. Young children are especially vulnerable because they often ingest soil from their hands or from objects they place in their mouths. Touching (making skin contact with) contaminated soil, dust, or water (for example, during recreational use of contaminated water bodies). Once toxic air pollutants enter the body, some persistent toxic air pollutants accumulate in body tissues. Predators typically accumulate even greater pollutant concentrations than their contaminated prey. As a result, people and other animals at the top of the food chain who eat contaminated fish or meat are exposed to concentrations that are much higher than the concentrations in the water, air, or soil.
TYPES OF POLLUTANTS? • • PRIMARY AIR POLLUTANTS : those emitted directly from identifiable sources. CO, CO 2, SO 2, NO 2, Most Hydrocarbons, most suspended particles or suspended particulate matter. SECONDARY AIR POLLUTANTS: When primary pollutants interact with one another, sunlight or natural gases to produce new, harmful compounds SO 3, HNO 3, H 2 SO 4, H 2 O 2, O 3 etc .
Primary Air Pollutants • Five major materials released directly into the atmosphere in unmodified forms. – Carbon monoxide – Sulfur dioxide – Nitrogen oxides – Hydrocarbons – Particulate matter
Carbon Monoxide • Produced by burning of organic material (coal, gas, wood, trash, etc. ) • Automobiles biggest source (80%) • Cigarette smoke another major source • Toxic because binds to hemoglobin, reduces oxygen in blood • Not a persistent pollutant, combines with oxygen to form CO 2 • Most communities now meet EPA standards, but rush hour traffic can produce high CO levels
Sulfur Dioxide • • • Produced by burning sulfur containing fossil fuels (coal, oil) Coal-burning power plants major source Reacts in atmosphere to produce acids One of the major components of acid rain When inhaled, can be very corrosive to lung tissue London – 1306 banned burning of sea coal – 1952 “killer fog”: 4, 000 people died in 4 weeks • tied to sulfur compounds in smog
Nitrogen Oxides • Produced from burning of fossil fuels • Contributes to acid rain, smog • Automobile engine main source • New engine technology has helped reduce, but many more cars
Hydrocarbons • Hydrocarbons organic compounds with hydrogen, carbon • From incomplete burning or evaporated from fuel supplies • Major source is automobiles, but some from industry • Contribute to smog • Improvements in engine design have helped reduce
Particulates • Particulates - small pieces of solid materials and liquid droplets (2. 5 mm and 10 mm) • Examples: ash from fires, asbestos from brakes and insulation, dust • Easily noticed: e. g. smokestacks • Can accumulate in lungs and interfere with the ability of lungs to exchange gases. • Some particulates are known carcinogens • Those working in dusty conditions at highest risk (e. g. , miners)
Secondary Pollutants • • Ozone PAN (peroxy acetyl nitrate) Photochemical smog Aerosols and mists (H 2 SO 4)
Ozone • Ozone (O 3) is a highly reactive gas composed of three oxygen atoms. • It is both a natural and a manmade product that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere). • Tropospheric ozone – what we breathe -- is formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds (VOC) and nitrogen oxides (NOX).
PAN Smog is caused by the interaction of some hydrocarbons and oxidants under the influence of sunlight giving rise to dangerous peroxy acetyl nitrate (PAN).
Photochemical smog • Photochemical smog is a mixture of pollutants which includes particulates, nitrogen oxides, ozone, aldehydes, peroxyethanoyl nitrate (PAN), unreacted hydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.
Aerosols and mists (H 2 SO 4) • Aerosols and mists are very fine liquid droplets that cannot be effectively removed using traditional packed scrubbers. These droplets can be formed from gas phase hydrolysis of halogenated acids (HCl, HF, HBr), metal halides, organohalides, sulfur trioxide (SO 3), and phosphorous pentoxide (P 2 O 5).
POLLUTANT STANDARD INDEX[ PSI OR AQI] The Pollutant Standards Index, or PSI, is a type of air quality index, which is a number used to provide the public with an easily understandable indicator of how polluted the air is. The pollutant standards Index is a uniform method recommended to classify and report urban air quantity. Five criteria pollutants are judged for the amount and adverse effects on human health. Initially, PSI was based on five air pollutants, but since 1 April 2014, it has included fine particulate matter (PM 2. 5). On that basis the air quality evaluated is designated as presenting “hazardous conditions” if the PSI is greater than 300, “very unhealthful conditions” if the PSI is between 201 and 300; “Unhealthy conditions” if PSI is between 101 and 200; “moderate conditions” if PSI is between is 51 to 100; “good conditions” if PSI is between is 0 to 50. The PSI for one day rises above 100; that is, to the ‘alert’ level or higher , when any one of the five criteria pollutants reaches a level that may be judged to have adverse effects on human health.
http: //app 2. nea. gov. sg/anti-pollution-radiation-protection/air-pollution-control/psi
Ambient Air Quality standards & Limits
Air Pollution Monitoring [http: //www. epa. gov/airquality/montring. html] The basic mission of the Office of Air Quality Planning and Standards is to preserve and improve the quality of our nation's air. To accomplish this, OAQPS must be able to evaluate the status of the atmosphere as compared to clean air standards and historical information.
Air Quality Standards OAQPS manages EPA programs to improve air quality in areas where the current quality is unacceptable and to prevent deterioration in areas where the air is relatively free of contamination. To accomplish this task, OAQPS establishes the National Ambient Air Quality Standard (NAAQS) for each of the criteria pollutants. There are two types of standards -- primary and secondary. Primary standards protect against adverse health effects; secondary standards protect against welfare effects, such as damage to farm crops and vegetation and damage to buildings.
AS PER EPA http: //www. epa. gov/air/criteria. html
CONTINUE….
Central Pollution Control Board 2006 National Ambient Air Quality Standards POLLUTANTS Sulphur dioxide (SO 2) Oxides of Nitrogen (NO 2) AVERAGE Annual average 24 hour TIME CONCENTRATION 60 µg/m 80 µg/m 3 3 A. A 60 µg /m 3 24 H 80 µg /m 3 A. A 140 µg/m 3 24 H 200 µg/m 3 Lead A. A 24 H 0. 75 µg/m 1. 0 µg/m Carbon Monoxide A. A 24 H 2. 0 µg/m 4. 0 µg/m A. A 60 µg/m 24 H 100 µg/m Suspended Particulate Matter ( SPM) Respirable Particulate Matter (RPM) 3 3 3
National Ambient Air Quality Standards[2009] (http: //cpcb. nic. in/National_Ambient_Air_Quality_Standards. php)
NAAQS by USEPA 2006 Pollutant Primary Stds. Averaging Times Secondary Stds. Carbon Monoxide 9 ppm (10 mg/m 3) 8 -hour(1) None 35 ppm (40 mg/m 3) 1 -hour(1) None Lead 1. 5 µg/m 3 Quarterly Average Same as Primary Nitrogen Dioxide 0. 053 ppm (100 µg/m 3) Annual (Arithmetic Mean) Same as Primary Particulate Matter (PM 10) Revoked(2) Annual(2) (Arith. Mean) 150 µg/m 3 24 -hour(3) 15. 0 µg/m 3 Annual(4) (Arith. Mean) 35 µg/m 3 24 -hour(5) 0. 08 ppm 8 -hour(6) Same as Primary 0. 12 ppm 1 -hour(7) (Applies only in limited areas) Same as Primary 0. 03 ppm Annual (Arith. Mean) ------- 0. 14 ppm 24 -hour(1) ------- Particulate Matter (PM 2. 5) Ozone Sulfur Oxides ------- 3 -hour(1) Same as Primary 0. 5 ppm (1300 µg/m 3) (1) Not to be exceeded more than once per year. (2) Due to a lack of evidence linking health problems to long-term exposure to coarse particle pollution, the agency revoked the annual PM 10 standard in 2006 (effective December 17, 2006). (3) Not to be exceeded more than once per year on average over 3 years. (4) To attain this standard, the 3 -year average of the weighted annual mean PM 2. 5 concentrations from single or multiple community-oriented monitors must not exceed 15. 0 µg/m 3. (5) To attain this standard, the 3 -year average of the 98 th percentile of 24 -hour concentrations at each population-oriented monitor within an area must not exceed 35 µg/m 3 (effective December 17, 2006). (6) To attain this standard, the 3 -year average of the fourth-highest daily maximum 8 -hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0. 08 ppm. (7) (a) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0. 12 ppm is < 1, as determined by appendix H. (b) As of June 15, 2005 EPA revoked the 1 -hour ozone standard in all areas except the fourteen 8 -hour ozone nonattainment Early Action Compact (EAC) Areas.
WHO Air Quality Guidelines Value Pollutant Averaging time AQG value 1 year 24 hour(99 th percentile) 10 µg/m 3 25 µg/m 3 PM 10 1 year 24 hour(99 th percentile) 20 µg/m 3 50 µg/m 3 Ozone, O 3 8 hour, daily maximum 100 μg/m 3 1 year 1 hour 40 μg/m 3 200 μg/m 3 24 hour 10 minute 20 μg/m 3 500 μg/m 3 Particulate matter PM 2. 5 Nitrogen dioxide, NO 2 Sulfur dioxide, SO 2 Source: WHO, 2005. WHO air quality guidelines global update 2005, WHOLIS number E 87950.
Ambient Air Pollution Monitoring
Introduction • Most frequently occurring pollutants in an urban environment are particulate matters (suspended particulate matter i. e. SPM and respirable suspended particulate matter i. e. RSPM), carbon monoxide (CO), hydrocarbons (HC), sulfur dioxide (SO 2), nitrogen dioxide (NO 2), ozone (O 3) and photochemical oxidants.
Monitoring of Air pollutants Source Point SOX NOX CO PM Ambient Line CO NOx HC RPM As per WHO ambient monitoring protocol SOx Essential NOx SPM HC CO Additional Source monitoring instruments O 3 Stack sampler (APM 620): Parameters monitored are a. Pollutants b. Velocity (Isokinetic) c. Temperature d. Pressure
The recommended criteria for siting the monitoring stations The site is dependent upon the use/purpose of the results of the monitoring programs. The monitoring should be carried out with a purpose of compliance of air quality standards. Monitoring must be able to evaluate impacts of new/existing air pollution sources. Monitoring must be able to evaluate impacts of hazards due to accidental release of chemicals. Monitoring data may be used for research purpose.
Type of ambient monitoring stations Station type Description Type A Downtown pedestrian exposure station- In central business districts, in congested areas, surrounding by buildings, many pedestrians, average traffic flow > 10000 vehicles per day. Location of station- 0. 5 m from curve; height 2. 5 to 3. 5 m from the ground. Type B Downtown neighbor hood exposure stations- In central business districts but not congested areas, less high rise buildings, average vehicles < 500 vehicles per day. Typical locations like parks, malls, landscapes areas etc. Location of station- 0. 5 m from curve; height 2. 5 to 3. 5 m from the ground. Type C Residential population exposure station – In the midst of the residential areas or suburban areas but not in central business districts. The station should be more than 100 m away from any street. Location of station- 0. 5 m from curve; height 2. 5 to 3. 5 m from the ground. Type D Mesoscale stations – At appropriate height to collect meteorological and air quality data at upper elevation; main purpose to collect the trend of data variations not human exposure. Location – roof top of tall buildings or broadcasting towers. Type E Non-urban stations – In remote non-urban areas, no traffic, no industrial activity. Main purpose to monitor trend analysis. Location of station- 0. 5 m from curve; height 2. 5 to 3. 5 m from the ground. Type F Specialized source survey stations – to determine the impact on air quality at specified location by an air pollution source under scrutiny. Location of station- 0. 5 m from curve; height 2. 5 to 3. 5 m from the ground.
Frequency of data collection • Gaseous pollutants: continuous monitoring • Particulates: once every three days
Number of stations • Minimum number is three. • The location is dependent upon the wind rose diagram that gives predominant wind directions and speed. • One station must be at upstream of predominant wind direction and other two must at downstream pre dominant wind direction. • More than three stations can also be established depending upon the area of coverage.
Components of ambient air sampling systems • Four main components are: – – Inlet manifold Air mover collection medium flow measurement device Inlet manifold transports sampled pollutants from ambient air to collection medium or analytical device in an unaltered condition. The manifold should not be very long. Air mover provides force to create vacuum or lower pressure at the end of sampling systems. They are pumps. The collection mediums are liquid or solid sorbent or dissolving gases or filters or chamber for air analysis (automatic instruments). The flow device like rotameters measure the volume of air sampled.
Characteristics for ambient air sampling systems • Five important characteristics are: – – – collection efficiency sample stability recovery minimal interference understanding the mechanism of collection The first three must be 100% efficient. For e. g. for SO 2, the sorbent should be such that at ambient temperature it may remove the SO 2 from ambient atmosphere 100%. Sample must be stabled during the time between sampling and analysis. Recovery i. e. the analysis of particular pollutant must be 100% correct.
Basic considerations for sampling • Sample must be representative in terms of time, location, and conditions to be studied. • Sample must be large enough for accurate analysis. • The sampling rate must be such as to provide maximum efficiency of collection. • Duration of sampling must accurately reflect the fluctuations in pollution levels i. e. whether 1 -hourly, 4 -hourly, 6 -hourly, 8 -hourly, 24 -hourly sampling. • Continuous sampling is preferred. • Pollutants must not be altered or modified during collection.
Errors in sampling by HVS • Particulates may be lost in sampling manifold – so not too long or too twisted manifold must be used. • If ’isokinetic’ conditioned are not maintained, biased results may be obtained for particulate matters.
Advantages of HVS High flow rate at low pressure drop High particulate storage capacity No moisture regain high collection efficiency Low coast Not appreciable increase in air flow resistance Filter is 99% efficient and can collect the particles as fine as 0. 3 μm Absorption principle is 99% efficient in collecting the gases
Lecture-2 Stack Monitoring: techniques & instrumentation
Stack Sampling • The sample collected must be representative in terms of time and location. • The sample volume should be large enough to permit accurate analysis. • The sampling rate must be such as to provide maximum efficiency of collection. • The contaminants must not be modified or altered in the process of collection.
Diagrammatic view of stack sampling
• Impingers are glass bubble tubes designed for the collection of airborne particles into a liquid medium (Figure 1). • When using an air sampler, a known volume of air bubbles is pumped through the glass tube that contains a liquid specified in the method. • The liquid is then analyzed to determine airborne concentrations. Figure 1: Glass Impinger
Selection of sampling location • The sampling point should be as far as possible from any disturbing influence, such as elbows, bends, transition pieces, baffles. • The sampling point, wherever possible should be at a distance of 5 -10 diameters down-stream from any obstruction and 3 -5 diameters up-stream from similar disturbance.
Size of sampling point • The size of the sampling point may be made in the range of 7 -10 cm, in diameter.
Traverse points • For the sample become representative, it should be collected at various points across the stack. • The number of traverse points may be selected with reference to Table 1: Traverse Points
In circular stacks, traverse points are located at the center of equal annular areas across two perpendicular diameters as shown in Figure 2 In case of rectangular stacks, the area may be divided in to 12 to 25 equal areas and the centers for each area are fixed. (Figure 3) Figure 3
Isokinetic conditions • Isokinetic conditions exist when the velocity in the stack ‘Vs’ equals the velocity at the top of the probe nozzle ‘Vn’ at the sample point (Figure 4). Figure 4
Lecture-3 Experimental analysis: Gaseous & particulates; standards & limits
Principles of Sampling and Analysis • The components of an air pollution monitoring system include the – collection or sampling of pollutants both from the ambient air and from specific sources, – the analysis or measurement of the pollutant concentrations, and – the reporting and use of the information collected. • Emissions data collected from point sources are used to determine compliance with air pollution regulations, determine the effectiveness of air pollution control technology, evaluate production efficiencies, and support scientific research.
Conti…. • The EPA has established ambient air monitoring methods for the criteria pollutants, as well as for toxic organic (TO) compounds and inorganic (IO) compounds. • The methods specify precise procedures that must be followed for any monitoring activity related to the compliance provisions of the Clean Air Act. • These procedures regulate sampling, analysis, calibration of instruments, and calculation of emissions. • The concentration is expressed in terms of mass per unit volume, usually micrograms per cubic meter (µg/m 3).
Particulate Monitoring • Particulate monitoring is usually accomplished with manual measurements and subsequent laboratory analysis. • A particulate matter measurement uses gravimetric principles. Gravimetric analysis refers to the quantitative chemical analysis of weighing a sample, usually of a separated and dried precipitate. • In this method, a filter-based high-volume sampler (a vacuum- type device that draws air through a filter or absorbing substrate) retains atmospheric pollutants for further laboratory weighing and chemical analysis. Particles are trapped or collected on filters, and the filters are weighed to determine the volume of the pollutant. The weight of the filter with collected pollutants minus the weight of a clean filter gives the amount of particulate matter in a given volume of air. • Chemical analysis can be done by atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively couple plasma (ICP) spectroscopy, and X-ray fluorescence (XRF) spectroscopy.
Atomic Absorption Spectrometry (AAS) • AAS is a sensitive means for the quantitative determination of more than 60 metals or metalloid elements. • Principle: This technique operates by measuring energy changes in the atomic state of the analyte. For example, AAS is used to measure lead in particulate monitoring. Figure: Atomic absorption spectrometry
Conti…. • Particles are collected by gravimetric methods in a Teflon (PTFE) filter, lead is acid-extracted from the filter. • The aqueous sample is vaporized and dissociates into its elements in the gaseous state. The element being measured, in this case lead, is aspirated into a flame or injected into a graphite furnace and atomized. • A hollow cathode or electrode less discharge lamp for the element being determined provides a source of that metal's particular absorption wavelength. • The atoms in the unionized or "ground" state absorb energy, become excited, and advance to a higher energy level. • A detector measures the amount of light absorbed by the element, hence the number of atoms in the ground state in the flame or furnace. • The data output from the spectrometer can be recorded on a strip chart recorder or processed by computer. • Determination of metal concentrations is performed from prepared calibration curves or read directly from the instrument.
Gaseous pollutant monitoring • Gaseous pollutant monitoring can be accomplished using various measurement principles. • Some of the most common techniques to analyze gaseous pollutants include – – – Spectrophotometry, Chemiluminescence, Gas chromatography-flame ionization detector (GC-FID), Gas chromatography-mass spectrometry (GC-MS), and Fourier transform infrared spectroscopy (FTIR).
Conti… • With all sampling and analysis procedures, the end result is quantitative data. • The validity of the data depends on the accuracy and precision of the methods used in generating the data. • The primary quality control measure is calibration. • Calibration checks the accuracy of a measurement by establishing the relationship between the output of a measurement process and a known input.
Table 1. Methods of Measuring and Analyzing Air Pollutants Variable Measured Principle Gravimetric PM 10, PM 2. 5 Particles are trapped or collected on filters, and the filters are weighed to determine the volume of the pollutant. Atomic absorption spectrometry (AAS) more than 60 metals or metalloid elements (e. g. Pb, Hg, Zn) This technique operates by measuring energy changes in the atomic state of the analyte. Emitted radiation is a function of atoms present in the sample. SO 2, O 3 Measure the amount of light that a sample absorbs. The amount of light absorbed indicates the amount of analyte present in the sample. Chemiluminescence NO 2, O 3 Based upon the emission spectrum of an excited species that is formed in the course of a chemical reaction. Gas chromatography (GC) - flame ionization detector (FID) VOC Responds in proportion to number of carbon atoms in gas sample. Method Spectrophotometry Gas chromatographymass spectrometry (GC- VOC MS) Mass spectrometers use the difference in mass-tocharge ratio (m/z) of ionized atoms or molecules to separate them from each other. Fourier Transform Infrared Spectroscopy (FTIR) Sample absorbs infrared radiation and difference in absorption is measured. CO, VOC, CH 4
Spectrophotometry • A spectrophotometer measures the amount of light that a sample absorbs. • The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector. • Spectrophotometry commonly used to measure sulfur dioxide (SO 2) concentrations. • The amount of light absorbed indicates the amount of sulfur dioxide present in the sample. Figure: Schematic of a UV-VIS spectrophotometer
Chemiluminescence • An ambient air sample is mixed with excess ozone in a special sample cell. A portion of the NO present is converted to an activated NO 2 which returns to a lower energy state and in the process emits light. This phenomenon is called chemiluminescence. Figure: Chemical reaction to determine oxides of nitrogen by chemiluminescence
Conti…. • Chemiluminescence methods for determining components of gases originated with the need for highly sensitive means for determining atmospheric pollutants such as ozone, oxides of nitrogen, and sulfur compounds. • The intensity of this light can be measured with a photomultiplier tube and is proportional to the amount of NO in the sample. A second reaction measures the total oxides of nitrogen in the air sample and in turn, the concentration of NO 2 can be calculated.
Gas Chromatography (GC) • Gas chromatography (GC) coupled with a flame ionization detector (FID) is employed for qualitative identification and quantitative determination of volatile organic compounds (VOCs) in air pollution monitoring. • The GC, consists of a column, oven and detector. In the gas chromatograph, a sample goes to the column, separates into individual compounds and proceeds through the hydrogen flame ionization detector. Figure: Schematic gas chromatography
Conti…. • The flame in a flame ionization detector is produced by the combustion of hydrogen and air. • When a sample is introduced, hydrocarbons are combusted and ionized, releasing electrons. • A collector with a polarizing voltage located near the flame attracts the free electrons, producing a current that is proportional to the amount of hydrocarbons in the sample. • The signal from the flame ionization detector is then amplified and output to a display or external device. • Gas chromatography-mass spectrometry (GC-MS) instruments have also been used for identification of volatile organic compounds. Mass spectrometers use the difference in mass-to-charge ratio (m/z) of ionized atoms or molecules to separate them from each other. Mass spectrometry is useful for quantification of atoms or molecules and also for determining chemical and structural information about molecules.
Fourier Transform Infrared Spectroscopy • FTIR can detect and measure both criteria pollutants and toxic pollutants in ambient air • FTIR can directly measure more than 120 gaseous pollutants in the ambient air, such as carbon monoxide, sulfur dioxide, and ozone. • The technology is based on the fact that every gas has its own "fingerprint, " or absorption spectrum. Figure: FTIR can directly measure both criteria pollutants and toxic pollutants in the ambient air. • The FTIR sensor monitors the entire infrared spectrum and reads the different fingerprints of the gases present in the ambient air.
Conti…. • Carbon monoxide is monitored continuously by analyzers that operate on the infrared absorption principle. • Ambient air is drawn into a sample chamber and a beam of infrared light is passed through it. • CO absorbs infrared radiation, and any decrease in the intensity of the beam is due to the presence of CO molecules. • This decrease is directly related to the concentration of CO in the air. • A special detector measures the difference in the radiation between this beam and a duplicate beam passing through a reference chamber with no CO present. • This difference in intensity is electronically translated into a reading of the CO present in the ambient air, measured in parts per million.
References • • • USEPA, 2007. Online literature from www. epa. gov WHO, 2005. WHO air quality guidelines global update 2005, WHOLIS number E 87950. CPCB 2006, Central Pollution Control Board. http: //www. cpcb. nic. in/standard 2. htm
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