GATE Environmental Engineering Air and Noise Pollution Syllabus

Air and Noise Pollution syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Air and Noise Pollution in GATE Environmental Engineering, not a summary of it.

1. 1

   Structure of the atmosphere

   2 topics

   • Natural and anthropogenic sources of pollution
   • Atmospheric sources, sinks, transport
2. 2

   Indoor air pollution

   1 topic

   • Effects on health and environment
3. 3

   Air pollution: gases and particulate matter

   2 topics

   • Air quality standards
   • Primary and secondary pollutants
4. 4

   Criteria pollutants, ambient and source standards, air quality indices, visibility

   overview

   Examined as a single unit within Air and Noise Pollution — no further topic split in the official outline.

5. 5

   Particulate pollutants: measurement and control methods

   5 topics

   • Control of particulate air pollutants using gravitational settling chambers
   • Cyclone separators
   • Wet collectors
   • Fabric filters (Bag-house filter)
   • Electrostatic precipitators (ESP)
6. 6

   Gaseous Pollutants: Measurement and control methods

   3 topics

   • Control of gaseous contaminants: absorption
   • Adsorption
   • Condensation and combustion
7. 7

   Control of sulphur oxides, nitrogen oxides, carbon monoxide, and hydrocarbons

   2 topics

   • Vapour-liquid and vapour-solid equilibria
   • Diffusion, Fick’s law and interfacial mass transfer
8. 8

   Automotive emission controls, fuel quality, diesel particulate filters, catalytic convertors

   overview

   Examined as a single unit within Air and Noise Pollution — no further topic split in the official outline.

9. 9

   Air quality management: Point, line and area sources

   4 topics

   • Inventory
   • Influence of meteorology - wind rose diagrams, stability, mixing height, topography
   • Dispersion modelling
   • Monitoring
10. 10

    Noise pollution: Sources

    3 topics

    • Health effects
    • Standards
    • Measurement and control methods

Air and Noise Pollution flashcards for GATE Environmental Engineering

23 of 50 cards from the Air and Noise Pollution deck — real questions with worked answers.

1. How are sources of air pollution classified as natural versus anthropogenic? Give examples of each.

   Natural sources occur without human intervention (volcanic eruptions, forest fires, dust storms, sea-salt spray, biological decay, pollen). Anthropogenic sources arise from human activity (combustion of fossil fuels, vehicular exhaust, industrial processes, agriculture, power plants).

2. Distinguish between primary and secondary air pollutants with examples.

   Primary pollutants are emitted directly from a source ($\ce{CO}$, $\ce{SO2}$, $\ce{NO}$, particulates, hydrocarbons). Secondary pollutants form in the atmosphere by reactions among primary pollutants ($\ce{O3}$, PAN, $\ce{H2SO4}$, photochemical smog, $\ce{NO2}$ formed from $\ce{NO}$).

3. What is a 'sink' in atmospheric pollution, and name common sinks for pollutants.

   A sink is any process or medium that removes a pollutant from the atmosphere. Common sinks include vegetation and soil (absorption/adsorption), water bodies (dissolution), chemical reaction/oxidation, and removal by precipitation (wet deposition) and gravitational settling (dry deposition).

4. Define photochemical smog and state the key reactant that initiates its formation.

   Photochemical smog is a secondary pollutant mixture (ozone, PAN, aldehydes) formed when $\ce{NO_x}$ and volatile hydrocarbons react in the presence of sunlight (UV). Photolysis of $\ce{NO2}$ ($\ce{NO2 ->[h\nu] NO + O}$) initiates the cycle, with atomic oxygen forming ozone.

5. Write the photolytic ozone-formation reactions in the $\ce{NO2}$ photolytic cycle.

   $$\ce{NO2 ->[h\nu] NO + O}$$ $$\ce{O + O2 + M -> O3 + M}$$ $$\ce{O3 + NO -> NO2 + O2}$$ where M is a third body that absorbs excess energy.

6. What is PAN and how is it formed?

   PAN (peroxyacetyl nitrate, $\ce{CH3COOONO2}$) is a secondary pollutant and a powerful eye irritant formed in photochemical smog from the reaction of peroxyacetyl radicals with $\ce{NO2}$.

7. What are the six 'criteria' air pollutants typically covered by ambient air quality standards?

   Particulate matter ($\mathrm{PM_{10}}$ and $\mathrm{PM_{2.5}}$), sulphur dioxide ($\ce{SO2}$), oxides of nitrogen ($\ce{NO_x}$/$\ce{NO2}$), carbon monoxide ($\ce{CO}$), ozone ($\ce{O3}$), and lead ($\ce{Pb}$).

8. What is the difference between $\mathrm{PM_{10}}$ and $\mathrm{PM_{2.5}}$, and why is $\mathrm{PM_{2.5}}$ more hazardous?

   $\mathrm{PM_{10}}$ has aerodynamic diameter $\leq 10\ \mu\mathrm{m}$; $\mathrm{PM_{2.5}}$ has diameter $\leq 2.5\ \mu\mathrm{m}$. $\mathrm{PM_{2.5}}$ is more hazardous because fine particles penetrate deep into the alveoli and can enter the bloodstream, causing respiratory and cardiovascular disease.

9. List the major health effects of carbon monoxide ($\ce{CO}$) exposure and its mechanism.

   $\ce{CO}$ binds to haemoglobin forming carboxyhaemoglobin ($\ce{COHb}$) with ~200-250 times the affinity of $\ce{O2}$, reducing oxygen-carrying capacity. Effects: headache, dizziness, impaired coordination, asphyxiation, and death at high concentrations.

10. Name three major environmental (non-health) effects of air pollution.

    Acid rain (from $\ce{SO2}$ and $\ce{NO_x}$), stratospheric ozone depletion (from CFCs), global warming/climate change (from greenhouse gases), plus reduced visibility, damage to vegetation, and corrosion of materials.

11. Write the chemical reactions describing the formation of acid rain from $\ce{SO2}$.

    $$\ce{2SO2 + O2 -> 2SO3}$$ $$\ce{SO3 + H2O -> H2SO4}$$ Also $\ce{SO2 + H2O -> H2SO3}$ (sulphurous acid). Nitrogen oxides give $\ce{HNO3}$ similarly.

12. On what principle does a gravitational settling chamber operate, and which particle sizes does it effectively remove?

    It uses gravity: gas velocity is reduced so that particles settle out under their own weight via terminal settling velocity. It is effective only for large, heavy particles, typically $> 50\ \mu\mathrm{m}$ in diameter.

13. State Stokes' law for the terminal settling velocity of a small particle in the laminar regime.

    $$v_{t} = \frac{g\,d_{p}^{2}\,(\rho_{p} - \rho_{g})}{18\,\mu}$$ where $d_p$ = particle diameter, $\rho_p$ = particle density, $\rho_g$ = gas density, $\mu$ = gas viscosity, $g$ = gravitational acceleration.

14. For a horizontal-flow gravitational settling chamber, write the expression for the minimum particle diameter that can be completely removed.

    $$d_{p,\min} = \sqrt{\frac{18\,\mu\, Q}{g\,(\rho_p - \rho_g)\, B\, L}}$$ where $Q$ = volumetric flow rate, $B$ = chamber width, $L$ = chamber length. Equivalently, the chamber captures a particle if its settling time $\leq$ residence time.

15. Write the collection efficiency of a gravitational settling chamber in terms of settling velocity and geometry.

    $$\eta = \frac{v_t\, L}{H\, v} = \frac{v_t\, L\, B}{Q}$$ where $v_t$ = settling velocity, $L$ = length, $H$ = height, $B$ = width, $v$ = horizontal gas velocity, $Q = v\,B\,H$ = flow rate.

16. On what principle does a cyclone separator operate, and what is the typical effective particle size range?

    A cyclone uses centrifugal force generated by a spinning (vortex) gas flow to fling particles outward to the wall, where they fall into a hopper. It is effective for medium-sized particles, typically $5$–$10\ \mu\mathrm{m}$ and larger.

17. How does the centrifugal force on a particle in a cyclone compare to gravity, and what does this imply for cyclone performance?

    The centrifugal acceleration is $\dfrac{v_t^2}{r}$, which can be many times $g$. The separation factor $S = \dfrac{v_t^2}{r\,g}$; a larger separation factor (smaller radius, higher tangential velocity) gives higher collection efficiency for smaller particles.

18. Define the 'cut diameter' ($d_{pc}$) for a cyclone separator.

    The cut diameter is the particle diameter collected with 50% efficiency. $$d_{pc} = \sqrt{\frac{9\,\mu\, B_c}{2\pi\, N_e\, v_i\,(\rho_p - \rho_g)}}$$ where $B_c$ = inlet width, $N_e$ = effective number of turns, $v_i$ = inlet velocity.

19. What is a wet collector (scrubber), and what is its primary collection mechanism?

    A wet collector (scrubber) removes particulates and/or gases by bringing the gas stream into contact with a liquid (usually water). Primary mechanisms are impaction, interception, and diffusion of particles onto liquid droplets, plus absorption of soluble gases.

20. What is a venturi scrubber and why is it efficient for fine particulates?

    A venturi scrubber injects scrubbing liquid into a high-velocity gas stream at the venturi throat. The high relative velocity atomizes the liquid into fine droplets, giving high particle-droplet impaction. It can collect submicron particles (down to ~$0.5\ \mu\mathrm{m}$) with high efficiency but at high pressure drop/energy cost.

21. Describe the operating principle and effective size range of a fabric (bag-house) filter.

    Gas passes through woven or felted fabric bags; particles are captured by sieving, impaction, interception, and diffusion. A 'dust cake' builds up and enhances filtration. It is very efficient (>99%) even for fine particles down to ~$0.1$–$1\ \mu\mathrm{m}$.

22. Define the air-to-cloth ratio (filtration velocity) for a bag-house filter.

    The air-to-cloth ratio is the volumetric gas flow rate per unit of fabric area: $$\text{A/C} = \frac{Q}{A_{cloth}}$$ It has units of velocity (e.g. m/min) and is the superficial face velocity of gas through the fabric. Lower ratios give better collection and lower pressure drop.

23. Name the three common bag-cleaning methods used in fabric filters.

    Shaker (mechanical shaking), reverse-air (reverse gas flow collapses the bag), and pulse-jet (a burst of compressed air dislodges the cake). Pulse-jet allows online cleaning at higher A/C ratios.

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