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Atmosphere
UNIT 10 AIR QUALITY MONITORING AND
CONTROL
Structure 10.1 Introduction Objectives 10.2 Air Quality Indoor and Outdoor Air Quality Air quality Management System and Standards Measures of Air Quality 10.3 Air Quality Monitoring National Ambient Air Management Programme Ambient Air Sampling Methods of Ambient Air Analysis Analysis of Common Air Pollutants 10.4 Air Pollution Control 10.5 Summary 10.6 Terminal Questions 10.7 Answers
10.1 INTRODUCTION
‘Black Taj Mahal – By 2050’; a recent Central Pollution Control Board (CPCB) report in the leading newspaper of the national capital, gives a real gloomy picture of the state of air pollution today. According to World Health Organisation estimates , urban air pollution contributes each year to approximately 800,000 deaths and a loss of 4. million life years. You might have realised the devastating effects that air pollution can have while reading about it and its ill effects in previous units of this block. It is almost obligatory on the part of governmental and various nongovernmental agencies to formulate the air quality standards, have a reliable monitoring programme and follow suitable control measures to ensure good health of million of people living all over the globe. The consequences of implementing strategies and intervention of Supreme Court in India have shown some effects in major metropolitan cities. A scope of further improvement is still there.
The last unit of Block 3 is devoted to the air quality monitoring requirements for our country in a broader perspective. In this context, the meaning of terms like air quality, air quality standards, air quality monitoring etc., associated with air quality management system have been explained. In order to understand the concept of monitoring and control, principles of some of the monitoring methods used for the most critical air pollutants have also been described. These would provide the underlying concepts for the experiments related to air pollution described in Block 7.
The next block deals with the pollution aspects of other two components of atmosphere viz., water and soil.
Objectives After studying this unit you should be able to:
- define air quality and explain its significance,
- state the air quality standards followed world over and in India,
- explain air quality management system,
Air Quality Monitoring and Control
- describe the principles lying under the monitoring methods for common air pollutants, and
- explain the control measures for common air pollutants.
10.2 AIR QUALITY
In the previous unit you read about various types of air pollutants and the adverse effects caused by these on all living beings and materials. You would recall that the major air pollutants with severe health effects include, nitrogen and sulphur oxides, CO, hydrocarbons and aerosols etc. Further, the increasing atmospheric abundance of climatically important gases as CO 2 , methane and nitrous oxide contribute to the greenhouse effect of the atmosphere and may lead to global warming and other climatic changes. The rapidly growing population, urbanisation and industrialisation in India has made some of the cities like New Delhi, Mumbai, Chennai and Kolkata as the world’s most polluted ones. Of the 3 million premature deaths in the world that occur each year due to outdoor and indoor air pollution, the highest number are assessed to occur in India. It is, therefore, essential to formulate norms or standards for the desired level of air quality with an adequate margin of safety, to protect public health and property. Air quality is defined in terms of air quality standards and criteria, discussed in subsection 10.2.2.
The causes of air pollution and the air quality requirements are different in indoor and outdoor environments. Let us learn about the concerns of indoor and outdoor air quality.
10.2.1 Indoor and Outdoor Air Quality
Indoor air quality refers to the physical, chemical and biological characteristics of air in the indoor environment, within a building or an institutional area or commercial facility. It is a measure of the concentration of gases or particulates in the indoor air that are responsible for pollution. These may be due to inadequate ventilation, high temperature and humidity. The lack of ventilation does not let enough outdoor air to get in and dilute emissions from indoor sources and also does not carry the indoor air pollutants out of the building. The developing countries that make use of traditional fuels (i.e. solid biomass) for cooking in 60-80% of their households face maximum indoor air pollution. The indoor pollution is generally due to,
- release of gases from combustion within the building premises,
- release of volatile organic compounds from building materials like, carpets, adhesives, paint, cleaning materials etc.
- infiltration of gases and particulate matter from outside the building sources through open doors and windows.
- microbes contaminating the building interiors and ventilation systems.
The indoor air pollution has immediate as well as long- term effects. The immediate effects are irritation of eyes, nose, throat, headaches , dizziness and fatigue. The long- term effects may show up years after the exposure and include respiratory diseases, heart disease and cancer.
Outdoor air quality also called the ambient air quality on the other hand refers to the measure of air pollutants in the atmosphere. It takes into consideration six main components, which are
- Suspended particulate matter (SPM) / Respirable suspended particulate matter (RSPM)
- Carbon monoxide
- Oxides of nitrogen
The average adult breathes over 3,000 gallons of air everyday. Children breath even more air per pound of bodyweight and are more susceptible to air pollution.
The World Bank in 1992 designated indoor pollution in the developing countries as one of the four most critical global environmental problems.
Air Quality Monitoring and Control
- Different sets of standards are prescribed for (i) industrial areas (ii) residential, rural and other areas and (iii) sensitive areas, depending on the land use pattern.
Table 10.1 gives the National Ambient Air Quality Standards for SO 2 , oxides of nitrogen (as NO 2 ) , suspended particulate matter (SPM) respirable particulate matter (< 10μ), carbon monoxide, lead and ammonia for industrial, residential (rural and other) and sensitive areas.
Table 10.1: National ambient air quality standards for some pollutants Concentration in ambient air Pollutant
Time weighted average Industrial area
Residential, rural and other areas
Sensitive area
Annual Average* (^80) μg/m^3 60 μg/m^3 15 μg/m^3 Sulphur Dioxide (SO 2 ) (^) 24 Hours Average** (^120) μg/m^3 80 μg/m^3 30 μg/m^3
Annual Average* (^80) μg/m^3 60 μg/m^3 15 μg/m^3 Oxides of Nitrogen as NO 2 24 Hours Average** (^120) μg/m^3 80 μg/m^3 30 μg/m^3
Suspended^ Annual Average^360 μg/m^3 140 μg/m^3 70 μg/m^3 Particulate Matter (SPM) 24 Hours Average* (^500) μg/m^3 200 μg/m^3 100 μg/m^3
Respirable^ Annual Average*^120 μg/m^3 60 μg/m^3 50 μg/m^3 Particulate Matter (Size less than 10 μ ) (RPM)
24 Hours Average** (^150) μg/m^3 100 μg/m^3 75 μg/m^3
Annual Average* (^) 1.0 μg/m^3 0.75 μg/m^3 0.50 μg/m^3 Lead (Pb) 24 Hours Average** (^) 1.5 μg/m^3 1.0 μg/m^3 0.75 μg/m^3
8 Hours Average** 5.0 mg/m^3 2.0 mg/m^3 1.0 m g/m^3 Carbon monoxide (CO) (^) 1 Hour Average 10.0 mg/m^3 4.0 mg/m^3 2.0 mg/m^3 Annual Average* (^100) μg/m^3 Ammonia (NH 3 ) 24 Hours Average** (^400) μg/m^3
- Annual Arithmetic mean of minimum 104 measurements in a year twice a week 24 hourly at uniform interval. ** 24 hourly/8 hourly values should be met 98% of the time in a year. However 2% of the time, it may exceed but not on two consecutive days.
The legislative support for prevention and control of air pollution is provided by a central legislation called the Air (Prevention and Control of Pollution) Act 1981.
The quality of air at a given place is expressed in terms of certain parameters like, air quality index and exceedence factor. Let us understand the meaning and significance of these parameters.
10.2.3 Measures of Air Quality
You would have observed that the local air quality changes from day to day or even hour to hour. The weather forecasts and reports are a regular feature of newspapers and the news on radio and television. The information on daily air quality includes the data on several air pollutants. The quality of the air can be categorised on the basis of certain quantitative parameters based on actual and permissible (or standard) values of the pollutants in the given sample. Two such parameters are:
Atmosphere
- Air quality index (AQI) given by Environmental Protection Agency (EPA), USA
- Exceedence factor (EF) given by Central Pollution Control Board, India
Air Quality Index It is defined as a number, expressing the actual concentration of a given pollutant in a sample of air, obtained by assigning a value of 100 to the permissible value of the pollutant. It can be computed as per the following formula.
Actual concentration of a given pollutant in air AQI = (^) × 100 Permissible value of the same pollutant
AQI is directly proportional to the level of air pollution. A higher value indicates a greater health concern. In the air quality index given by EPA, the air (a range of numbers) represents quality values and the index also includes the health concerns with respect to the detected pollution level and the corresponding remedial measures. The AQI contains information about the five major air pollutants viz., ozone, particulate matter, carbon monoxide, sulphur dioxide and nitrogen dioxide. Once a value is determined for each of the five pollutants, the highest of the given numbers is reported as the pollutant standard index for the day.
EPA has divided the AQI into six categories, which correspond to different level of health concerns. These are represented by different colours. These categories along with their values, the health concerns and colour indication is given in Table 10.2.
Table 10.2: Various categories of AQI as per EPA of USA
Category designation AQI Value^ Related health effects^ Colour code
Good
Moderate
Unhealthy for sensitive groups
Unhealthy
Very unhealthy
Hazardous
0 – 50
51 – 100
101 – 150
151 – 200
201 – 300
301 – 500
Satisfactory, no risk
Acceptable for some pollutants, a moderate health concern for very small number of people unusually reactive to ozone, may experience respiratory symptoms. General public not affected.
Members of reactive groups may be affected, people with lung disease or heart disease are at greater risk
Health concern for all
A health alert every one may experience serious health effects.
Entire population affected, health warnings of emergency condition at AQI above 400, premature death of all and elderly persons may result.
Green
Yellow
Orange
Red
Purple
Maroon
Atmosphere (^) SAQ 2
Fill in the blank spaces with appropriate words.
The long-term standards of air quality are given on the basis of measurements done in _____ hours ______ a week in ______ year whereas the shortterm standards are prescribed by making measurements for ______, _______ and ___ hours everyday.
10.3 AIR QUALITY MONITORING
Increasing air pollution especially in urban areas, necessitates a constant monitoring schedule assessing the long and shortterm changes in air quality. A programme of this nature and magnitude needs the participation of masses. Therefore, we need to raise awareness amongst them and motivate them to participate. In India the air quality monitoring began in late 1960s. Initially it was done for only few pollutants like sulphur dioxide, nitrogen oxides and suspended particulate matter. Recently, monitoring of respirable particulate matter (RPM) has been started but a comprehensive and systematic monitoring for polynuclear aromatic hydrocarbons (PAH), ozone, carbon monoxide, benzene etc. is still not in place.
In a nation wide programme, called the National Ambient Air Monitoring Programme (NAMP) , CPCB has established a national network of ambient air quality monitoring stations. This was launched in 1984 with a network of 28 monitoring stations spread over 7 cities. Today the number of stations has increased to more than 295 spread over 92 cities distributed over 24 states and 4 union territories. Similar to the NAMP , many state boards have also set up ambient air quality monitoring stations at state level under their Ambient Air Quality Monitoring (AAQM) programmes. Under NAMP of CPCB, the National Environmental Engineering Research Institute (NEERI) monitors ambient air quality in 30 monitoring stations spread over 10 major cities. Some major industries have set up their own monitoring stations as a legal obligation.
The NAMP and state level AAQM stations monitor the pollutants (NO 2 , SO 2 and SPM) and meteorological parameters like wind speed, wind direction, temperature and humidity. NEERI on the other hand monitors certain special parameters like NH 3 , H 2 S, RSPM, PAH and heavy metals also in addition to these three conventional parameters. CPCB has been monitoring lead, PAH and other heavy metals in particulate matter, benzene, ozone and CO at some of its monitoring stations in Delhi. The objectives of the air quality monitoring programmes of this nature are :
- to strengthen the existing air monitoring system with the adoption of state-of-the- art methodologies.
- to monitor the pollutants depending on the locations.
- to determine present air quality status and trend.
- to provide background air quality data as required for industrial setting and town planning and
- to control and regulate pollution from industries and other sources to achieve the air quality standards.
10.3.1 National Ambient Air Management Programme As mentioned above the National Air Monitoring Programme (NAMP) is a nation- wide air monitoring network. Several agencies are involved in this programme. These are:
- Central Pollution Control Board (CPCB) in Delhi
- State Pollution Control Boards (SPCBs) in different states
Air Quality Monitoring and Control
- Pollution Control Committees (PCCs) in union territories
- National Environmental Engineering Research Institute (NEERI) in 10 cities
- Vishveshvaraiya Regional College of Engineering in Nagpur
- University of Pune
- KTHM college in Nasik
- Walchand Institute of Technology in Solapur
The job of coordinating with these agencies so as to ensure uniformity, consistency and compatibility of air quality data is entrusted with CPCB. It also provides technical and financial support to these agencies for operating the monitoring stations. The methods of measurement for the criteria pollutants are identified and notified in the ambient air quality standards by CPCB. The document on ambient air quality standards contains information on air pollutants, like SO 2 , NO 2 , SPM, RSPM, respirable lead and CO. These standards provide the basis for protec ting the public health from adverse effects of air pollutants and limiting these contaminants of air within the adequate margin of safety. The air quality data obtained from these monitoring stations is compiled in a report annually and published for the use of policy makers, researchers and general public.
Having learnt about the significance of monitoring the quality of air and various programmes being undertaken at different levels for the same, let us understand how is this task of monitoring executed? The first step in air quality monitoring is the collection of air sample. Let us try to understand the methods and apparatus used for it. Assess your understanding for so far you have read by answering the following SAQ.
SAQ 3
A list of pollutants is given in column A. In column B write the stations or institutes at which these are monitored.
A B
a) NO 2 , SO 2 and SPM at state level
b) NH 3 , H 2 S, RSPM, PAH, heavy metals
c) lead, PAH, heavy metals, ozone and CO
d) NO 2 , SO 2 and SPM and meteorological parameters at national level
10.3.2 Ambient Air Sampling
Analysis of air sample is difficult because of its very nature. The inherent difficulties are due to varied nature of the pollutants in it, the low concentrations to be determined, concentration variations with respect to time and location, variations in the meteorological factors like temperature, wind and humidity etc. Another problem is with the collection of the sample itself as the desired sampling point may well be quite away from the ground.
General Considerations in Sampling Air
An air sample should be true representative for a particular place and time. Since there is a possibility of errors being encountered during sampling procedure, some basic principles should be followed while collecting an air sample. These are as given below.
Most of the monitoring activities under the NAMP and AAQM programmes are confined to industrial, residential and commercial areas. However, the monitoring facilities need to be se up in the reserved forests, wild life sanctuaries and near the monuments etc.
Air Quality Monitoring and Control
Fig. 10.1: Schematic sketch of a sampling train
The collection of a sample containing particulate matter requires filtration, impinging (for both liquid and solid samples ) or precipitation whereas for gases and vapours, sample is collected by adsorption on a solid surface, absorption in a liquid or by freezing (or condensation) or filling in an evacuated container. Let us learn about the methods used for ambient air sampling. These are given under two heads.
- Collection of particulate matter
- Collection of gas or vapour samples
Collection of Particulate Matter
The particulate matter (liquid or solid) can be collected by a number of methods. Some of the commonly used methods are given below:
Filteration : It is one of the most commonly employed technique for collecting particulate matter from an air sample. A variety of filters are employed depending on the nature of the particulates. Metals and anions are filtered through cellulose filter papers while organic compounds are collected with the help of glass fibres or silica felts. Trace inorganic species on the other hand are filtered through silica felts. However, now a days the membrane filters are a general choice because of high flow rates. A high volume sampler used for collecting large volume of particulate matter by filteration technique is shown schematically in Fig. 10.2.
Fig. 10.2: Schematic diagram of high volume sampler used for collecting SPM
Atmosphere (^) Inertial method : In this method a stream of air sample containing particulate matter is
collided (impinged) against a flat surface. There are two types of impingers i.e., the wet type and dry impingers or impactors. In wet impingers the air stream is collided against a flat surface that is immersed in some liquid whereas the impactors use dry surfaces. The efficiency of this method depends on the size of the particles being collected. These collectors are good for particles of diameter> 1μ. For smaller particles the velocity of the stream is sufficiently increased.
Centrifugal method : In this method the air sample containing particulate matter is passed with high velocity through a cylindrical glass chamber. It creates a kind of cyclonic motion in which the particles separate due to centrifugal field and get collected in the sedimentation chamber. This method is limited to the particles of a diameter of 5μ or above but gives a dry and chemically pure sample.
Gradient method : This method makes use of different physical properties (electrical mobility, thermal and diffusion) of particulate matter and collects particles of 0.001 to 0.01μ m. Electrostatic and thermal samplers are used for this pur pose. In electrostatic sampler the particles pass through an electric discharge between two electrodes maintained at a high potential difference ( of the order of 30,000 V). The particles pick up charges and move towards the electrodes of opposite charge where they lose their charge and get struck to the electrode. These accumulated particulates can then be recovered and analysed. The schematic diagram of an electrostatic sampler is shown in Fig. 10.3.
In case of thermal samplers the particles are made to pass through a temperature gradient and tend to move towards the regions of low temperature. These get accumulated in the low temperature regions. These samplers are good for aerosol particles of 0.001μ dimensions. The larger versions of these samplers are used to control the emission of particulates.
Fig. 10.3: Schematic diagram of electrostatic sampler used for collecting SPM Collection of Gas or Vapour Samples Gas sample collection is done by a different way and involves the following processes.
Absorption : In this method the gases are passed through liquid absorbents where these get absorbed. Absorption depends upon the surface area of the absorbent, time of absorption, and rate of the reaction between absorbent and gas. This process is suitable for the absorption of oxides of carbon, sulphur and nitrogen besides some others. For example CO is absorbed in ammonical cuprous chloride; SO 2 in hydrogen peroxide; CO 2 in alcoholic potash and ozone in potassium iodide.
Atmosphere (^) Chemical Methods
You may be familiar with these methods and would have used these in your previous chemistry labs. These involve some chemical reaction between the pollutant being determined and a suitable reagent and include the following techniques.
Volumetric measurements : These are related to volume measurement and may be any of the following types depending on the type of reaction involved like, neutralisation, oxidation, reduction or precipitation etc.
Gravimetric determ inations : These are related to mass measurements. These involve converting an analyte ( the pollutant to be analysed) to a solid precipitate and measuring its mass. The mass of the precipitate so obtained is a measure of the concentration of the pollutant.
Colorimetric determinations : These are related to optical determination of concentration of coloured components. Here, the analyte gives a coloured product with the reagent. The optical density of the solution is a measure of the concentration of the product.
Turbidimetric and nephelometric determinations : These are based on optical measurement of light passing through the suspension.
Chromatographic determinations : These are based on adsorption and absorption phenomenon using paper, column etc.
Instrumental Methods These methods make use of a number of spectrophotometric techniques. The basic principle involved in these is given below in brief. The details can be found in Unit 19 of Block 6.
Emission Spectrometry : The metallic elements when subjected to suitable excitation by means of heating at high temperatures emit radiation of characteristic wavelengths. The intensity of radiation emitted can be correlated with the quantity of the element present. The energy emitted at some wavelength in the spectrum of a given element is proportional to the number of excited atoms and thereby to the concentration of the element in the sample. Thus using emission spectrometry both qualitative and quantitative estimation can be done.
Absorption Spectrometry : It is based on absorption spectrometric method where absorption of a certain range of electromagnetic radiation in visible, ultraviolet and infrared regions of the spectrum takes place. The amount of radiation absorbed is directly proportional to the concentration of the absorbing species.
Atomic Absorption Spectroscopy (AAS): The principle is quite like atomic emission spectrometry. Here the radiation is absorbed by atoms in ground-state (vapour) by atoms at a specific wavelength. The atoms in excited state emit radiation to come to ground state. The amount of energy absorbed and emitted is a function of the number of atoms present. Thus the method gives a quantitative estimation of atoms in trace amounts and is a sensitive method for pollution analysis.
Biological Methods These methods are of indirect nature. Here the pollutant which has infected a plant or an animal can be extracted from the source and be analysed. Both suspended particulate matter and gaseous pollutants can be estimated using this method.
Air Quality Monitoring and Control
The monitorin g methods used by NAMP for different pollutants are compiled in Table 10.5.
Table 10.5: Air pollution monitorin g methods used by NAMP
Serial No.
Pollutant Method employed
1 SPM High volume sampler 2 RSPM High volume sampler with an attached cyclone 3 SO 2 Colorimetry
4 NO 2 Colorimetry 5 CO Non-dispersive IR spectroscopy 6 Pb Acid digestion followed by AAS analysis 7 PAH Solvent extraction followed by GC-FID analysis 8 H 2 S Colorimetry
9 NH 3 Colorimetry
Let us learn the possible methods of analysing some of the common air pollutants. Before proceeding try to answer the following SAQ.
SAQ 4
Tick (√) mark in front of correct and ( x ) mark in front of wrong statements given below.
a) Analysis of an air sample is difficult because a chemical reaction is not possible with it. b) Particulate matter is to be generally collected by filtration methods. c) Emission spectrometry is based on the principle of absorption of a particular radiation by an air pollutant. d) Titration method for SO 2 analysis in an air sample makes use of its oxidising nature.
10.3.4 Analysis of Common Air Pollutants
Besides some meteorological parameters you will be studying the detailed methods of analysis of some common air pollutants in Block 7 of this course pertaining to the experiments. The experiments are to be performed during your laboratory work at the study centre. Some methods in general for a few of the pollutants are given below.
Suspended Particulate Matter
Analysis of SPM is done using high volume method. It is called so because it makes use of a high volume sampler (Fig.10.2) for collecting large volume of air containing particles. The sample is collected through a preweighed filter for 8 hours. The filter is reweighed to find out the weight of particulate. The amount of particulate matter is calculated by the following equation:
f i 10 g/m w w SPM × μ
−
V Where, wi = initial weight of filter in g wf = final weight of filter in g V = volume of air sampled in m 3
Air Quality Monitoring and Control
given air sample may also contain NO 2 which will not be measured as such because these molecules are in ground state. Therefore, these are converted to NO by passing the air sample over a thermal convertor. Fig. 10.5 shows a diagrammatic sketch of chemiluminescence detector.
Fig. 10.5: Schematic diagram of a chemiluminescence detector
2) Spectrophotometry : In this method, the sample of air is bubbled through a solution of sodium hydroxide and sodium arsenite so as to collect nitrite ion produced. The NO 2 ion are determined colorimetrically by reacting with phosphoric acid, sulphanilamide and N–(1-naphthyl) ethylenediamine dihydrochloride (NEDA). The absorbance of the highly coloured azo dye ( reddish purple) formed is measured on a spectrophotometer at 540 nm. The range of concentration of NOx measured by this
method at a sampling rate of 200 cm^3 min−^1 for 24 hours is 0.01-0.40 ppm.
Sulphur Dioxide
There are a number of methods used for the determination of the amount of SO 2 like titration, reduction, gravimetry and photometry. Two of these are given below.
1) Titration : A sample of air containing SO 2 is bubbled through hydrogen peroxide where it produces H 2 SO 4 which can be measured by titration with a standard alkali.
S O 2 + H 2 O 2 H^2 S O^4
This reaction can be used to determine SO 2 conductometrically also because the formation of acid would increase the conductance. Alternatively , the air sample containing SO 2 is bubbled through a solution of KI and liberated iodine is titrated with a standaradised solution of sodium thiosulphate in a redox titration.
2) Spectrophotometry : This is the most reliable method. Here SO 2 is passed through a solution of potassium tetrachloromercurate, K 2 HgCl 4 (TCM), resulting in the formation of highly stable complex. The complex is made to react with pararosaniline and formaldehyde to form an intensely coloured pararosaniline methylsulphonic acid. The absorbance of the solution is measured by means of a suitable spectrophotometer at a wavelength of 560 nm. Concentration of sulphur dioxide in the range of 25 – 1050 μ g /m^3 can be measured by this method. Concentration below 25μ g /m^3 can be measured by sampling larger volumes of air. The details of this method are given in Experiment 18 of Block 7.
Atmosphere
SO 2
Formaldehyde
TCM
Pararosaniline methylsulphonic acid
Colorimeter ( 560 nm)
Air sample containing
10.4 AIR POLLUTION CONTROL
After monitoring and finding out the levels of air pollutants in atmosphere, the next obvious step is to initiate control measures. The strategy for air pollution control entails a multipronged approach including legal, technological and economic components. If the concentration of the pollutants is within the desired limits then we have to take measures to maintain these and in case these are higher then we need to take suitable damage control measures. It is difficult to have control on some natural phenomenon like volcanoes or spread of pollens etc., however control of air pollutants which are anthropogenic in nature can be done at the source itself. There are a number of ways, some of which are as follows.
ß Placing a control equipment at source so as to reduce the discharge of pollutant. ß Change in process by changing raw material, operation or the equipment. ß Change in fuel so as to reduce emission. ß Increasing stack height to reduce the discharge. ß Removal of pollutant; though complete removal of pollutant is a tough task. ß Relocating industries causing pollution.
Of these, reduction of the pollutant discharge at the source by using control equipment is the most effective method. General methods of control of SPM and gaseous air pollutants by control equipment is given in the following paragraphs.
Suspended Particulate Matter SPM can be controlled by following methods.
Using filters : The filters can be cloth, screen or felt pad to remove SPM. These can be gravitational setting or thermal precipitators. As discussed earlier, thermal precipitators work on temperature gradient.
Using electrostatic precipitator (ESP ): These can work at high temperatures also and ideal to remove SPM. However, it is useless for combustible particulates.
Inertial collection : This is the cheapest method. A cyclone device is used to collect large particles of 10μ m size. The change of radius of curvature, particle size and diameter and gas flow influence working of cyclone. Wet collection is also possible using wet scrubbers.
Gaseous Air Pollutants Conversion to a non-polluting form is the best method for control of gaseous pollutants. However, the sampling methods, generally used for these pollutants, are also appropriate for their control. These are as follows.
Absorption : the gaseous pollutants are absorbed in wet scrubber using a suitable liquid. SO 2 , H 2 S, HC l, Cl 2 and NH 3 are collected by absorption in a suitable liquid while for halogens water can also be used.
Adsorption : the pollutants are adsorbed on surface of solids. Porous materials like alumina, silica and activated coal are generally used for absorption. There can be regenerated on heating.
Atmosphere (^) The quality of ambient air is monitored by national netw ork of ambient air quality
monitoring stations established by CPCB, under a programme called the National Ambient Air Monitoring programme (NAMP). In addition, a number of State Pollution Control Boards (SPCBs), research institutes, NGOs and industries are contributing towards ambient air quality monitoring. The monitoring of air quality involves collecting appropriate samples and analysing them using chemical, instrumental and biological methods. Once the status of air quality is determined, suitable control measures are initiated to ensure the desired levels of air quality and a clean air experience.
10.6 TERMINAL QUESTIONS
- What is meant by air quality? State the major air quality concerns.
- Which agency at national level is responsible for the air quality monitoring? What
are its main objectives?
- What are the various air components monitored by various monitoring agencies?
- What are the basic methods used for particulate matter sampling and gaseous pollutants sampling?
- What is the best method used for i) CO analysis ii) SO 2 analysis and iii) NO 2 analysis.
- List various methods of controlling SPM and gaseous air pollutants.
10.7 ANSWERS
Self Assessment Questions
- b)
- 24, twice, one, one, eight, 24
- a) AAQM, SPCB b) NEERI, Nagpur c) CPCB, Delhi d) NAMP, CPCB
- a) (X) b) (√ ) c) (X) d) (√ )
Terminal Questions
- Air quality is defined by the criteria, standards and criteria ascertained for the air pollutants, which is required to be such that it does not cause too many ill-effects for living and non-living matter. The two major concerns are indoor and outdoor air quality.
- Central Pollution Control Board at national level is responsible for air quality monitoring. Its main objectives are to strengthen the air monitoring systems, monitor the pollutants regularly on location basis, determine present air quality status and trend and control and regulate air pollution from industries and other sources.
Air Quality Monitoring and Control
- The air components monitored are SO 2 , CO, NO 2 , SPM, RSPM, benzene, PAH, ozone, heavy metals and meteorological parameters.
- For particulate matter inertial, centrifugal and gradient methods are used, gaseous pollutants are collected by ways of adsorption, absorption and condensation.
- i) Non-dispersive infrared spectroscopy ii) Spectrophotometer iii) Chemiluminescence
- SPM can be controlled by using filters, ESP and inertial collection. For gaseous pollutants absorption, adsorption, combustion and condensation methods are used.
FURTHER READINGS
- Environmental Chemistry, A.K. De, New Age International (P) Ltd, New Delhi 1995.
- Air Pollution, M.N. Rao, H.V.N. Rao, Tata Mc Graw Hill, New Delhi 1992.
- Environmental Chemistry, Stanley E. Manahan, Lewis Publishers 2000.
