Soirces, effect, sampling and measurements of air pollution and photochemical reaction

Sources and effects of particulate and gaseous air pollutants

TYPES OF SOURCES

1. NATURAL SOURCES

• Volcanic ash and gasses
• Smoke and harmful trace gasses from forest fires
• Dust storms

2. ANTHROPOGENIC SOURCES

• Combustion:
• Combustion of fossil fuels: SOX, NOx, CO, PM, water vapor and traces of metal oxides of mercury, lead & cadmium.
• incineration of solid combustible wastes: aldehydes, benzo- pyrene, CO, NOx,SO2 , PM, HCs, NH3
• Chemical & metallurgical industries:

• Iron & steel industry: dust, fumes, HC, H2S, SO2
• Non-metallic mineral industries (cement, glass, ceramics refractories): hazardous dust
• Chemical process industries: HF, SO2, HCl, C6H6, C6H5CH3, Cl4, NO3, NH3, SO4.
• Petroleum refining operations: oxides of S and S containing vapors, particulates from catalyst regenerations and recycling H2S & mercaptans
• Pulp & paper industry: HH S & mercaptansHS, methyl mercaptan, methyl sulphides, particulates
• Food processing industries: dust, odors, nitrates &phosphates, pesticides, arsenic & lead particulate

Effects of particulate and gaseous air pollutants

1. Ozone can cause to more frequently asthma attacks in people who have asthma and can cause sore throats, coughs, and breathing difficulty.
2. Carbon monoxide makes hard for body parts to get the oxygen.
3. High levels of nitrogen dioxide exposure can give people coughs and can make them feel short of breath.
4. Particulate matter that is small enough that can enter the lungs and cause health problems. Some of these problems include more frequently asthma attacks, respiratory problems, and premature death also.
5. Sulfur dioxide exposure affects people who have asthma or emphysema and difficult for them to breathe.
6. Toxic air pollutants can cause cancer and birth defects in an organism.
7. The greenhouse gasses causes the increases temperature of the earth.

Photochemical reactions

A chemical reaction initiated by light is called photochemical reaction. The branch of science which deals this type of reaction is photochemistry. In general, photochemistry is the domain that concerns with various photochemical reactions. In photochemical reactions energy is received in a form of light.

1. Mechanism of photochemical reaction

From absorption of light energy by the reactants molecules which is sufficient to break the covalent bond. We know that E = he / λ, we see that longer wavelength visible light (400 to 800 nm) is more less energetic (70 to 40 kcal/mole) than light in the available shorter wavelength (200 to 400 nm) near ultraviolet region (150 to 70 kcal/mole). One example of photochemical reactions is given below:

1. Photosynthesis of hydrochloride (HCl) gas:

Formation of hydrochloride gas in presence of light.

H2 (g) + Cl2 (g) + hν ——————> 2 HCl (g)

1. Photosynthesis in plant:

Plants use solar energy to convert carbon dioxide and water into glucose and oxygen.

b. Photosynthesis of Vitamin D by human skin in the presence of sunlight.

2. Features of Photochemical Reactions

1. Photochemical reactions do not take place in a dark but take place in the presence of light by absorbing it.
2. Only particular wavelength light can initiate the photochemical reaction (definite range of frequencies
3. Temperature has very little effect on the rate of a photochemical reaction. Instead, the intensity of light has marked effect on the rate of photochemical reaction.
4. The free energy change of a photochemical reaction may not be negative.
5. There are many substances which do not react directly in the presence of light. However, if another substance is added, the photochemical reaction starts.

3. Uses of Photochemical Reaction

• Bioluminescence:

In fireflies, an enzyme in the abdomen catalyzes a reaction that produced light.

• .Photodynamic therapy:

Light is used to destroy tumors by the action of singlet oxygen generated by photosensitized reactions of triplet oxygen.

• Photo degradation of medical drugs. So, medical drugs are stored in dark bottles.
• .Synthesis of various organic compounds such as enzymes, medicines, etc. has been possible due to use and advancement of photochemistry in organic field. The field is also called organic photochemistry.

4. Negative aspects of Photochemical Reaction:

• Formation of photochemical smog, fog, etc.
• Formation of ozone at lower atmospheric level.
• Formation of oxides of nitrogen and sulfur (NOx and Sox).
• Ozone layer depletion due to an action of CFCs and NOx on stratospheric ozone.

5. Photochemical smog

It is the pollution result by the complex reactions between the sunlight and the pollutants like nitrogen oxide, hydrocarbons. It is mainly caused by the exhaust of automobiles and different industrials. Simply it is the formation of smog by the photochemical reaction. It causes the breathing problem, respiratory tract illness, eye irritation and some other different hazardous diseases.

Condition

1. Air stagnation
2. Abundant sunlight
3. High concentration of so2 and no2.

Air pollution sampling and measurement

To get the detail pollution information of specific air both qualitatively and quantitatively sampling of air and its measurement is done on the following aspects such as sources of air pollution, topography, population distribution, land use pattern, climatology. It also gives the information about the atmospheric behavior of the given location. There are two types of sampling,

1. Continuous sampling

In this type of sampling data is carried out by automatic sensors, optical or electrochemical, and spectroscopic methods which produce continuous records of concentration values.

b. Time-averaged sampling

In this type of sampling data can then be obtained from continuous records. Time-averaged data can also be obtained by sampling a known volume of air for the given averaging time. Thus the samples are then analyzed by established physical, chemical, and biological methods for the concentration values which are the effective average over the period of sampling.

Sampling includes,

1. a) Selection of sampling procedures including procedures of analysis of samples
2. b) Sampling locations
3. c) Period of sampling, frequency of sampling and duration
4. d) Auxiliary measurements (including meteorological parameters)
5. e) Processing of data

Measurement

Measurement of air pollution includes,

1. Selection of measurement point
2. Mass transfer measurement
3. Dynamic flow rate
   1. Sampling flow rate can be obtained by the dynamic method using suction pumps.
4. Static flow rate
   1. When the vapor diffusion method for standard gas generation and molecular diffusion method for air sampling are adopted without using power such as a suction pump, mass transfer is obtained by the static method.

Measurement of gaseous air pollution includes,

• Natural ventilation method
• Vacuum vessel method
• Sampling method on the dynamic flow
• Displacement method
• Reaction solution absorption method

Measurement of Total suspended particulate, PM10 and PM 2.5

1. TECHNIQUES AVAILABLE TO MEASURE PM

• Physical basis

Direct

• Mass concentration (µg/m 3)
• Number concentration (particles/m 3)
• Total vs. size-selective aerosols (TSP vs. PM x)

Indirect

• Active (transmissometer, nephelometry, aethalometer)
• Passive (target imaging)

• Time basis

Time-averaged

• Ambient standards (24-hr, annual)
• Occupational standards (8-hr, 30-min)
• Federal or state reference methods
• Obscures short-term phenomena
• Relatively inexpensive to buy but may be expensive to run

Continuous/instantaneous

• More information; can be used to compute time averages
• Equivalent methods
• Relatively high capital expense, but lower labor requirements

TYPES OF PARTICULATE MATTER AND MEASUREMENT METHODS PARTICULATE MATTER (PM)

They have suspended droplets or solid particles or the mixture of the two. Particulates can be composed of inert or extremely reactive materials, ranging in size (i.e. diameter from 100 μm to 0.1 μm or less). PM may either be primary pollutants such as smoke particles or a secondary pollutant formed from the chemical reaction of gaseous pollutants such as dust, smoke, plant spores, bacteria, salt, fumes, mist, fog, and aerosol. Human activities resulting in PM in air includes mining, burning of fossil fuels, transportation, and agriculture. The size of particles also determines its potential impact on human health. Large particles are usually trapped in the nose and throat and swallowed. Smaller particles may reach the lungs, cause irritation of eye and skin problem.

1. CLASSIFICATION OF PM

• Dust
• It contains particles of size ranging from 1 to 200 μm.
• It is formed by natural disintegration of rock and soil or by the mechanical processes of grinding and spraying.
• They have large settling velocities & are removed from the air by gravity and other inertial processes.
• Fine dust particles act as centers of catalysis for many of the chemical reactions taking pace in the atmosphere.

Smoke

• It contains fine or very small liquid or solid particles.
• Size ranges from 0.01 to 1μm in diameter.
• It is formed by incomplete combustion or by other chemical processes.
• It may have different colors depending upon the nature of other materials burnt.

Fumes

• They are solid particles of sizes ranging from 0.1 to 1μm.
• They are released from chemical and metallurgical processes.

Mist

• It is made up of liquid droplets having the size less than 10μm.
• It is formed by condensation in an atmosphere or is released from industrial operations.

Fog

• It is the air-borne liquid having the size of 1 to 100μm.
• It is the mist in which the liquid is water & is sufficiently dense to obscure vision.

Smog

• It implies an air mixture of smoke particles, mists and fog droplets of such concentration and composition as to impart visibility in addition to being irritating or harmful.
• The composition varies widely between the different locations and times (0.01 to 0.1μm).
• Smog + fog + mist => visibility reduced.

Aerosol

• It includes all air-borne suspensions either sold or liquid having the size smaller than 1μm.

Total suspended particulate (TSP)

• Microscopic solid or liquid matter suspended in the Earth's atmosphere. They are complex, multi-phase system of all airborne solid and low-vapor-pressure liquid particles having aerodynamic particle sizes from below 0.01 μm to 100 μm and larger.

2. HEALTH EFFECT OF PM

• Particulates change the climatic condition by affecting incoming and outgoing radiation. Particulates are mainly responsible for failure in forecasting of climatic changes.
• Particulates cause different health problems. PM₁₀ gets settled in bronchi and causes serious lungs problems. PM₅ has the high chance of penetrating in the gas exchanging region of lungs and causes severe damage to other organs.
• Beside human beings, these particulates also have negative impact on animals and plants
• Particulate matters also cause a problem in aviation sector like decreasing of engine efficiency.

3. Measurement

High-Volume Air Sampling method

• it was the Federal Reference Method (FRM) for measuring compliance with the TSP particulate matter standard
• A high-volume sampler with a 7- by 9-inch exposed filter area operated in a standard shelter at a sampling flow rate of 1.1 to 1.7 cubic meters per minute (39 to 60 cubic feet per minute) collects particles of up to 25 to 50 µm in aerodynamic diameter, depending on wind speed and direction, and uniformly distributes the sample over the filter surface
• Operates at 40 cm
• Captures TSP on an 8”x10” fiberglass
• Filter processing required
• Pre-exposure conditioning to RH temp specs
• Pre-exposure weighing
• Post-exposure conditioning
• Post-exposure weighing

THINGS TO BE RECORDED FROM SAMPLER

• Filter serial number
• Sampling site identification number and/or address
• Sampler identification number
• Starting time
• Initial sampling flow rate
• Sampling date (including day, month, and year)
• Summary of conditions that may affect results (e.g., meteorology, construction activities, etc.)
• Operator’s initials or signature
• Ambient temperature and barometric pressure

PM₁₀

• particulate matter with an aerodynamic diameter less than or equal to a nominal 10µm (PM 10 ) in ambient air
• reparable that is, they can be inhaled below the nasopharynx area (nose and mouth)
• include dust, pollen and mold spores

FEDERAL REFRENCE METHOD FOR PM₁₀

• Low volume air sampling method
• Currently used for compliance monitoring
• Size-selective inlet collects larger particles on oily impactor surface
• Operates at 40 cfm
• Captures PM 10 on an 8”x10” fiberglass filter
• Filter processing required
• FRMs also exist for PM 2.5 compliance monitoring
• The alkalinity of filter medium should be less than 2.5 microequivalents/gram for FRM. The filters should be equilibrated at constant relative humidity of between 20 percent and 45 percent ±5 percent for FRM
• The precision of collocated FRM samplers must be 5 µg/m3 for PM concentration below 80 µg/m 3 and 7 percent for PM10 concentration above 80 µg/m 3 for FRM
• The FRM requires the air flow rate through the sampler remain stable over a 24-hour period, regardless of filter loading; the specific requirements are ±5 percent of the initial reading for the average flow, and ±10 percent of the initial flow rate for any instantaneous flow measurement

PM_2.5

• fine particulate matter, having an aerodynamic diameter less than or equal to 2.5 µm , in ambient air
• particles below 2.5mm travels down below the tracheobronchial region (into the lungs)
• include combustion particles, organic compounds and metals

Federal Reference Method (FRM) for PM_2.5

• measures the mass concentration of fine particulate matter, having an aerodynamic diameter less than or equal to 2.5 µm , in ambient air over a 24-hour period
• The measurement process is considered to be nondestructive, and the PM 2.5 sample obtained can be subjected to subsequent physical or chemical analyses
• The suspended particulate matter in the PM 2.5 size range is separated from the larger particles and then collected on a polytetrafluoroethylene (PTFE) filter
• The total volume of air sampled at actual temperature and pressure conditions is calculated from the measured flow rate and sampling time
• Each filter is weighed (after moisture and temperature conditioning) before and after sample collection to determine the net gain in weight of PM 2.5
• The mass concentration of PM 2.5 collected, in micrograms per cubic meter (µg/m 3 ), is calculated by dividing the net gain in weight by the total volume of air sampled

FEDERAL EQUIVALENT METHOD (FEM) FOR PM_2.5

• These methods are not required to be based on filter collection of PM₅
• Equivalent methods are not necessarily required to meet all the requirements specified for FRMs but measurement precision should met
• Classified into different classes for sampling

References:
1. Mackenzie L. Davis & David A. Cornwell, “Introduction to Environmental Engineering”, McGraw Hill.
2. Gilbert M. Masters, Standford University, “Introduction to Environmental Engineering and Science”, Printice Hall.
3. Stephan Konz, Kansas State University, “Work design”, Grid Publishing Inc., Colombus, Ohio
4. C. S. Rao, “Environmental Pollution Control Engineering”, New age International (P) Limited, Publishers, India.