BITS Pilani
K K Birla Goa Campus
EE ZG514/ SSTM ZG516: Environmental Sampling
and analytical methods
Lecture - 2
Dr. Sharad M. Sontakke
Department of Chemical Engineering
Summary of Lecture 1
Module 1 (part 1): Structure and function of pollutants, and
analysis
• Need of environmental sampling and analysis
• Qualitative and quantitative analysis
• Structural formula
• Functional group
• Concentration unit
• Organic and inorganic pollutants
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Contents
Module 1 (part 2): Structure and function of pollutants, and
analysis
• Source of pollutants
• Common analytical methods
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Organic pollutants
These includes organic compounds such as:
• Phenols,
• Organic dyes,
• Polyaromatic hydrocarbons,
• Polychlorinated biphenyls,
• Pesticides,
• Pharmaceuticals,
• Polymers, etc.
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Inorganic pollutants
These include:
• Heavy metals and trace elements such cadmium
(Cd), chromium (Cr), arsenic (As), lead (Pb), mercury
(Hg), Fluoride (F), etc.,
• Oxides of metal,
• Inorganic ions: Chloride (Cl‒), Sulfate (SO42‒),
(NO3‒), Phosphate (PO32‒), etc.
• Metal salts, etc.
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Sources
Organic
Dyes
Textile
Tanning
Paper
Chemical
Phenols
Textile
Petroleum
Metallurgy
Chemical
Detergents
Dairy
Food processing
Laundry
Organo-pesticides
Agriculture
Food processing
Acids
Textile
Metallurgy
Chemical
Alkali
Textile
Metallurgy
Chemical
Metals
Textile
Metallurgy
Agriculture
Metallic salts
Tanning
Paper
Metallurgy
Cyanides
Metallurgy
Inorganic
Laundry
Agriculture
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Sources of some inorganic pollutants:
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Source of Air pollutants:
Natural or anthropogenic
• Natural: wind-blown, pollen, sea salt, volcanic ash and
gases , etc.
• Anthropogenic: combustion of fossil fuels, water vapor,
trace metal oxides, incineration, coal and iron ores
• Industrial sources: cement, glass, ceramic, refractories,
power plant, refineries, pulp and paper, food processing
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Particulate matter
In general, particulate matter (PM) refers to all atmospheric
substances that are not gases.
They include suspended droplets, solid particles or mixture of
these.
The PM can include inert to very reactive materials ranging in
size from 100 μm down to 0.1 μm or less.
The inert material do not react with the environment
whereas, the reactive materials may react chemically.
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Classification:
Dust: It contains particles of the size ranging from 1-200 μm.
These are released due to natural disintegration of rocks
and soil or by mechanical processes of grinding spraying.
Fine dust particles acts as a catalyst for many chemical
reactions in the atmosphere.
Smoke: These contains fine liquid or solid particles (ranging
between 0.01-1 μm) released as a result of combustion or
other chemical process. It may have different colors based
on the material burnt.
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Fumes: These contains fine solid particles (ranging between
0.1-1 μm) released from chemical or metallurgical
processes.
Mist: Made up of liquid droplets generally smaller than 10
μm. These are formed by condensation or released from
industrial operations.
Fog: Mist in which liquid is water and sufficiently dense to
blur vision.
Aerosol: Includes air-borne suspension (solid or liquid)
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Sources of particulate matter
Fossil fuel combustion:
Fossil fuels are an anthropogenic source of particulate matter
(PM). Coal, oil, natural gas, gasoline, and diesel fuel all
produce some PM.
Combustion of gasoline in an automobile engine emits
particles of organic material (soot), Si, Fe, Zn, and S.
Diesel-powered trucks emit 10 to 100 times more particulate
material than do gasoline-powered vehicles; most of this
PM takes the form of organic material from unburned fuel.
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The combustion of coal releases soot, sulfate, and fly ash.
Coal is a solid fossil fuel that was formed millions of years
ago by compaction of partially decomposed plant material.
The classes of coal are distinguished by their percentage of
carbon, which is directly related to their heating value.
Seams of coal also form with other natural minerals such as
iron pyrite (FeS).
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Some fraction of the minerals produces particles of fly ash,
so named because smaller particles of ash that are
produced enter the furnace flue and “fly up” the
smokestack.
The size (diameter) of the fly ash largely determines whether
it will be removed from the stack gases by electrostatic
precipitators or bag houses; these systems easily remove
larger-diameter particles.
Coal-fired boilers produce approximately 1% to 2% fly ash,
with a diameter of 0.1 µm.
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Even though this small-diameter fraction represents only 1%
to 2% of the coal-combustion emissions by weight, it
accounts for the largest number of particles and most of
the surface area.
Fly ash from coal-fired boilers has been shown to contain Fe,
Zn, Pb, V, Mn, Cr, Cu, Ni, As, Co, Cd, Sb, and Hg.
This smaller fly ash is an inhalation risk; smaller particles are
less likely to be trapped in the nose or larynx and are more
likely to be inhaled into the deep recesses of the lung.
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Industrial Sources
Some industrial processes involve burning metals in
conjunction with fossil fuels. Waste incineration and kiln
drying of cement are two examples of industrial processes
in which metals are emitted.
The PM resulting from this kind of industrial process usually
contains Fe2O3, Fe3O4, Al2O3, SiO2, and metal carbonates.
In
such processes, heavy metals vaporize at high
temperature and then recondense onto particles that are
formed simultaneously.
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Miscellaneous Sources
Rubber particles from tires, pollen, viruses, and meteoric
debris are all commonly found in the air.
In automobiles, rubber particles (usually larger than 2 µm) are
constantly produced due to wearing of tires.
Plants and biological organisms produce pollen and viruses.
Meteorites that impact the stratosphere release Fe, Ti, and Al
particles as they heat from the friction of entry into the
atmosphere.
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Water quality assessment
Source: https://www.mpcb.gov.in accessed on 24 Sep, 2020
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Color:
The presence of color in water is unacceptable for drinking or
other purposes.
Color in water may result from the presence of metals,
organic acids, microbiological matter and/or industrial
wastes.
The platinum-cobalt method (EPA Method 110.2) is useful for
comparing the color of potable water and of water in which
color is due to naturally occurring materials. However, this
method is not appropriate for highly colored industrial
wastewater.
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This method was originally intended for visual comparison by
matching sample color with calibrated glass slides or with
standards made from dilutions of potassium chloroplatinate
and cobaltous chloride in distilled water.
Spectrophotometric method (EPA Method 110.3) is used for
analysis of color from domestic as well as industrial water.
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Analysis of trace elements
Trace elements such as Arsenic, Boron, Barium, Beryllium,
Cadmium, Chromium, Mercury, Lead, Silver, etc. can be
analyzed using an Atomic Absorption
Spectrophotometer.
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Analysis of Air pollution
To understand the chemistry of atmosphere, measurements
of concentration of the gaseous components in the
atmosphere is an important aspect.
The measurements may be made in two different ways:
1) In situ: which means the sample of the atmospheric gases
is placed inside the device (spectrometer) that is making
the measurement, and
2) Remotely (remote-sensing technique): by passing a beam
of energy that originates on a satellite, an aircraft, the
space shuttle, or the ground through a portion of the
atmosphere that is to be studied.
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In Situ Absorption
Measurements
Spectroscopic measurements rely on the fact that different
chemical compounds absorb electromagnetic radiation at
different wavelengths.
When a molecule absorbs a photon of electromagnetic
radiation, the energy of the molecule increases.
For example, when a molecule absorbs microwave radiation,
which is electromagnetic radiation of a relatively low
energy, it stimulates only the rotational motion of the
molecule.
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Image source: Girard, Principles of Environmental Chemistry
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Infrared (IR) radiation, which has higher energy than
microwaves, stimulates the vibrations of molecules that
absorb it.
Ultraviolet (UV) radiation, which has even more energy than
IR, causes electrons in the molecules absorbing it to be
promoted into higher-energy orbitals; the molecule is said
to be in the excited state.
Very high-energy electromagnetic radiation, such as an Xray, has enough energy to break chemical bonds and
ionize molecules.
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When the sample absorbs a beam of electromagnetic
radiation, the irradiance (intensity or radiant power) of the
beam is decreased.
Irradiance (P) is the energy per second per unit area of the
light beam.
Figure: A single-beam spectrophotometric instrument.
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Electromagnetic
radiation
is
passed
through
a
monochromator (a prism or filter) to select one wavelength
of electromagnetic radiation.
The light of a single wavelength is said to be monochromatic
(having single color). The monochromatic light, with
irradiance Po, passes into a sample of length b.
The irradiance of the beam emerging from the other side of
the sample is P. Because some of the light may be
absorbed by the sample, P ≤ Po.
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Transmittance (T) is defined as the fraction of the original
light that has passed through the sample.
T = P/Po
T has the range of 0 to 1. The percentage of transmittance
is 100T; it has a range from 0% to 100%.
Absorbance (A) is defined as follows:
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When no light is absorbed, P = Po and A = 0.
Absorbance is important because it is directly proportional to
the concentration (c) of the absorbing molecules in the
sample.
The relationship between the concentration of the absorbing
molecules and absorbance has been described by the
Beer-Lambert law, more simply known as Beer’s law:
A = ԑbc
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Absorbance is dimensionless; thus all of the constants and
variables on the right side of the equation must have units
that cancel.
The concentration (c) of the sample can be expressed in
many ways. For example, moles per liter, ppm, parts per
billion (ppb), or mg/m3.
The path length (b) can be very small (cm) or very large (km).
The quantity ε is called the molar absorptivity (or extinction
coefficient)
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The molar absorptivity (ԑ) is the characteristic of a molecule
that indicates how much light it will absorb at a particular
wavelength; it can be expressed by using many different
units.
Depending on how the concentration and the path length are
expressed, ε must have a unit that makes the product of
(εbc) dimensionless.
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Infrared Spectrometry
IR spectroscopy is an useful technique for measuring
atmospheric constituents because major gas molecules
(except inert gases and homonuclear diatomic molecules
such as N2 and H2) absorb IR radiation at specific
wavelengths.
Molecules selectively absorb specific IR frequencies that
correspond to the frequencies of the vibrational oscillations
of the atoms, which are connected by covalent bonds.
When a molecule absorbs IR radiation, the amplitudes of
these vibrations increase.
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The absorption corresponding to these oscillations appears
in certain definite wavelength regions of the spectrum.
The frequency (𝜈) at which a characteristic IR absorption
occurs depends on the mass of the atoms involved in the
vibration and the strength of the bond connecting the
atoms.
Planck’s equation relates the energy (E) of the absorbed
radiation to its frequency: E=h𝜈 (where 𝜈, pronounce as
nu, h is a Planck’s constant = 6.6 * 10-34 Js)
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Fig: IR spectrum of
water vapor
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Infrared Vibrational
Frequencies
The absorption that is observed in the IR region can be
described by using a very simple model that calls for the
atoms in the molecule to be considered balls and the
bonds that connect them to be springs.
For a diatomic molecule, the two atoms have masses (M1
and M2), and the spring has a force constant (k).
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3*1010
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Monitoring Automotive
Emissions
Mobile sources of air pollution have a very large impact on
the air quality. Automobile emissions which releases
nitrogen oxide (NOx) and CO are among the major
gaseous pollutants.
Automobile Emissions: Hydrocarbons
The internal combustion engines used in automobiles and
trucks produce a complex mixture of organic molecules as
part of their emissions.
Depending on the air/fuel ratio of the engine and the
compression ratio, more or less HCs may be produced.
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The automobile emissions may contain saturated and
unsaturated HCs, aromatic HCs, and polynuclear aromatic
HCs, as well as alcohols, aldehydes, ketones, and ethers.
A detector that responds to almost all organic compounds
that contain carbon–hydrogen bonds is the flame
ionization detector, which uses a hydrogen/air flame to
burn organic molecules in a sample; in doing so, it
produces a current that is proportional to the carbon mass
flow into the flame.
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Fig: A schematic diagram of flame ionization detector for measurement
of hydrocarbons
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The dominant reaction that takes place in the hydrogen flame
is as follows:
The most stable ion in an HC flame is H3O+.
The current generated by the detector is carried from the
burner nozzle to the ion collector plate. An opposing
recombination reaction then reduces the signal output:
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The applied voltage between the collector plate and the
burner nozzle must be large enough that the ions do not
recombine before reaching the collector.
When HC molecules enter the flame ionization detector, they
are burned, and the current between the burner nozzle and
the ion collector plate increases proportionally to the
amount of HC that is present.
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Automobile Emissions: Nitrogen Oxides
The NOx in automobile tailpipe emissions are measured by
the use of chemiluminescence-that is, chemical reactions
that release energy in the form of light rather than heat.
In this case, the NO in the tailpipe emissions reacts with
ozone. The energy produced in this reaction is released as
light rather than as heat.
The reaction is a two-step process. In the first step, the ozone
reacts with the NO to produce an excited-state nitrogen
dioxide molecule (NO2*).
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In the second step of the reaction, the NO2* loses excess
energy as the excited electrons return to ground state and
emit the excess energy as a photon of light (hν).
The reactions can be written as follows:
In addition to NO, significant amounts of NO2 are usually
present in the automobile emission. If the tailpipe sample is
passed through a heated-activated carbon catalyst, the
NO2 can be converted to NO:
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The total amount of NOx, is the sum of NO and NO2 present.
To measure the amount of NO in the tailpipe gas stream, the
carbon catalyst is removed from the stream.
The difference between the two results gives the NO2 present.
The NO2* then loses energy and gives off electromagnetic
radiation (light) which is measured by photomultiplier.
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Fig: A schematic
diagram of the
chemiluminescent
analyzer (CLA) for
the measurement of
NOx in the autombile
emission
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Automobile Emissions: Carbon Monoxide
The amount of CO in tailpipe emissions is monitored by IR
spectrometry.
The dispersive IR take longer time (approx. 20-30 min) to get
the results and therefore, is not used for measurement of
tailpipe emissions.
CO emission monitoring uses an non-dispersive infra-red
(NDIR) spectrometer.
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Fig: A schematic
diagram of NDIR for the
analysis of CO in
automobile emission
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The NDIR analyzer uses a heated tungsten filament, which is
a broad-band source that emits across the IR region.
The reference cell is filled with nitrogen, and the sample to be
measured flows through the sample cell.
A flexible diaphragm separates the two sides of the detector.
Optical filters are placed between the IR source and the
sample and reference cell to remove IR wavelengths that
would be absorbed by CO2 in the sample.
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When a sample containing CO is present in the sample cell,
IR energy from the source will be absorbed, and less IR
energy will reach the sample side of the detector cell.
The difference in IR energy reaching the two halves of the
detector produces a small pressure imbalance between
the detector cells, which in turn causes the diaphragm
between the cells to bend.
A constant voltage applied between the detector plate and
the diaphragm causes a current to flow when the distance
changes.
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Summary
In this lecture we discussed:
Sources of major pollutants
Typical analytical methods for the analysis of water
pollutants and air pollutants
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Questions
1. What are the typical sources of dye pollutants?
2. What are the typical sources of HCs?
3. What are the typical sources of Lead?
4. What is the difference between Mist and Fog?
5. Which analytical method is used for detection of color
present in water?
6. Which analytical method is used for detection of trace
elements in water?
7. What is FTIR?
8. What is Beer-Lambert law? Is there any limitation on its
applicability?
9. What is FID? What is its used?
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Plan for next lecture
In the next lecture, we will discuss:
• Sampling methods
• Analytical data collection
• Common errors during analysis
• Standardization and calibration
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