(SEM VIII) THEORY EXAMINATION 2020-21 AIR AND NOISE POLLUTION CONTROL

AIR AND NOISE POLLUTION CONTROL – RCE 077

B.Tech (Semester VII) – Detailed Answers

SECTION A – Descriptive Answers (2 Marks Each)

a) Air Pollution

Air pollution is the presence of undesirable solid, liquid, or gaseous substances in the atmosphere in concentrations that are harmful to human health, plants, animals, materials, or the environment. These pollutants may originate from natural sources or human activities such as industries, vehicles, and burning of fossil fuels.

b) Sampling

Sampling is the process of collecting a representative portion of air or pollutant from the atmosphere for the purpose of analysis. Proper sampling ensures accurate measurement of pollutant concentration and assessment of air quality.

c) Stack Plume

A stack plume is the visible or invisible stream of gases emitted from an industrial chimney or stack into the atmosphere. The behavior and dispersion of the plume depend on meteorological conditions such as wind speed, temperature gradient, and atmospheric stability.

d) Indoor Air Pollution

Indoor air pollution refers to the contamination of air inside buildings due to pollutants generated within enclosed spaces.
 

Indoor air pollutants include:                              Carbon monoxide (CO)

Volatile organic compounds (VOCs)                       Tobacco smoke

Particulate matter                                                    Formaldehyde

e) Lapse Rate, DALR and ELR

Lapse Rate: Rate of decrease of atmospheric temperature with height.

DALR (Dry Adiabatic Lapse Rate): Temperature decrease of dry air parcel without heat exchange (≈9.8°C/km).

ELR (Environmental Lapse Rate): Actual temperature variation in the atmosphere with height.

f) Acoustic

The term acoustic relates to sound, including its generation, transmission, propagation, and perception. Acoustics deals with the study of sound waves and noise behavior in different environments.

g) Special Noise Environments

Special noise environments include:                       Airports

Railway stations                                                       Industrial zones

Construction sites                                                    High-traffic road intersections

SECTION B – Long Answers (7 Marks Each)

2(a) Effects of Noise Pollution

Noise pollution has several adverse effects on humans and the environment. It causes hearing loss, sleep disturbances, stress, hypertension, reduced work efficiency, and psychological disorders. Prolonged exposure to high noise levels may also lead to cardiovascular diseases. In wildlife, noise disrupts communication, breeding patterns, and migration.

2(b) Noise Control Standards and Air Pollution Control Technologies

Noise Control Standards:
Noise limits are prescribed for different zones such as residential, commercial, industrial, and silence zones by regulatory authorities.

Air Pollution Control Technologies:                   Gravitational settling chambers

Cyclone separators                                                 Fabric filters

Electrostatic precipitators                                       Scrubbers

These technologies remove particulate and gaseous pollutants from exhaust gases.

2(c) Electrostatic Precipitator (ESP)

An electrostatic precipitator removes fine particulate matter from flue gases using electrostatic forces. Polluted gas passes between charged electrodes, where particles become electrically charged and migrate toward collecting plates. Periodic rapping dislodges particles into hoppers.
Advantages: High efficiency, low pressure drop
Disadvantages: High initial cost, sensitive to gas composition

2(d) Catalytic Converter

A catalytic converter is an emission control device used in automobiles to reduce harmful exhaust gases. It uses catalysts like platinum, palladium, and rhodium.

Reactions:                                                               CO → CO₂

HC → CO₂ + H₂O                                                      NOx → N₂ + O₂

It significantly reduces carbon monoxide, hydrocarbons, and nitrogen oxides.

2(e) Gravitational Settling Chamber

This device removes large particulate matter by reducing gas velocity, allowing particles to settle under gravity.

Advantages: Simple design, low cost
Limitations: Ineffective for fine particles, large space requirement

SECTION C – Very Long Answers (7 Marks Each)

3(a) Fabric Filter (Baghouse)

A fabric filter removes particulate matter by passing polluted air through fabric bags. Dust particles are trapped on the fabric surface, forming a dust cake that enhances filtration efficiency. Periodic shaking or reverse air flow cleans the bags.
Efficiency: Up to 99% for fine particles
(Neat labeled diagram should be drawn in exam)

3(b) Control Technologies for Oxides of Sulphur (SOx)

SOx emissions are controlled using:                             Flue Gas Desulfurization (FGD)

Wet scrubbers                                                               Limestone injection

Use of low-sulphur fuels                                               Fluidized bed combustion

4(a) Meteorological Factors Influencing Air Pollution

Primary meteorological factors include wind speed and direction, temperature, atmospheric stability, mixing height, humidity, and solar radiation. These factors determine pollutant dispersion and concentration.

4(b) Atmospheric Stability and Inversion

Atmospheric stability describes the tendency of air to resist or enhance vertical motion.
Temperature inversion occurs when temperature increases with height, restricting pollutant dispersion.

Types of inversion:                                                      Radiation inversion

Subsidence inversion                                                    Advection inversion

Frontal inversion

5(a) Plume Behavior under Different Atmospheric Conditions

Different atmospheric conditions produce different plume shapes:

Looping plume: Unstable atmosphere                       Coning plume: Neutral conditions

Fanning plume: Stable atmosphere                            Lofting plume: Favorable dispersion
(Neat sketches required in exam)

5(b) Estimation of Plume Rise

Plume rise is estimated using formulas such as:          Briggs equation

Holland’s formula
Plume rise depends on exit velocity, temperature difference, stack height, and wind speed.

6(a) Equivalent Continuous Sound Level (Leq)

Leq is the constant sound level that contains the same acoustic energy as a fluctuating noise over a given period. It is widely used for environmental noise assessment.

6(b) Adsorption Sampling Techniques

Adsorption sampling uses solid sorbents like activated charcoal or silica gel to collect gaseous pollutants. After sampling, pollutants are desorbed and analyzed in laboratories.

7(a) Vehicular Pollutants and Euro Standards

Petrol Vehicles: CO, HC, NOx                                         Diesel Vehicles: NOx, particulate matter, SO₂

Euro Standards:                                                             Euro-I: Basic emission control

Euro-II: Reduced CO and HC                                          Euro-III: Stricter NOx and PM limits

7(b) Noise Pollution Control Methods

Ways to Reduce Noise:                                                 Source control (quieter machines)

Path control (barriers, enclosures)                                   Receiver protection (ear plugs, ear muffs)

Zoning and land-use planning                                        Proper maintenance of equipment