GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersAir pollutants, their health and crop effects, standards and indices, dispersion, and control equipment, plus noise. Agricultural sources (residue burning, ammonia, dust, odour) are covered here alongside the industrial ones GATE ES examines.
In the exams: GATE ES Section 6 (whole section, numerical); ICAR AICE subject 71 Unit 3; UGC NET Unit 6; state pollution control board recruitment
GATE — Environmental Science and Engineering, Section 6 (air and noise pollution)
Numerical problems on Gaussian plume ground-level concentrations, effective stack height, stability and mixing height, settling velocity and settling chamber efficiency, cyclones, ESP (Deutsch) and fabric filter design, series efficiency, emission estimation from fuel sulphur, AQI calculation, and decibel addition and distance attenuation; concepts of FGD, SCR and catalytic converters.
How our questions for GATE spread across the units of Air & Noise Pollution: Monitoring & Control. Difficulty: 16 easy, 51 medium, 22 hard.
| Noise: sources, effects, standards, measurement and control | 10 | |
| Particulate control: settling chambers, cyclones, wet scrubbers, fabric filters, ESP | 9 | |
| Meteorology and dispersion: stability, mixing height, wind rose | 8 | |
| Gaussian plume dispersion modelling | 8 | |
| Gaseous control: absorption, adsorption, condensation, combustion | 8 | |
| Control of SOx, NOx, CO and hydrocarbons; vehicle emissions | 8 | |
| Emission inventories for point, line and area sources | 8 | |
| Criteria pollutants, ambient and emission standards | 7 | |
| Indoor air pollution | 6 | |
| Sources and classification of air pollutants; primary and secondary | 5 | |
| Air quality indices and visibility | 5 | |
| Effects on human health, crops and materials | 5 | |
| Agricultural air pollution: residue burning, ammonia, dust and odour | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Why is airshed or regional management increasingly advocated over city-by-city control?
C. Much of a city's PM2.5 comes from outside it
Long-range transport and secondary formation mean regional sources contribute substantially, so coordinated action is needed.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
According to India's NAAQS (2009), what is the 24-hour standard for PM2.5?
B. 60 µg/m³
PM2.5: 40 annual, 60 24-hour. 100 is the PM10 24-hour standard; 15 is the WHO 2021 24-hour guideline.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
What is the WHO 2021 annual Air Quality Guideline for PM2.5?
C. 5 µg/m³
WHO lowered the annual PM2.5 guideline from 10 (2005) to 5 µg/m³ in 2021; India's NAAQS is 40.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
Which source dominates global atmospheric ammonia emissions?
A. Agriculture, mainly livestock manure and fertilisers
Agriculture contributes the large majority of NH3 emissions.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
Which formula has been used in India to set minimum stack height from SO2 emission rate Q (kg/h)?
C. H = 14Q^0.3
CPCB guidelines used H = 14Q^0.3 metres, with a minimum height for many industries.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
Activated carbon is mainly used to control which emissions?
D. Volatile organic compounds and odours
Activated carbon adsorbs VOCs and odours; dust needs particulate collectors; CO needs oxidation.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
What is 'breakthrough' in a fixed-bed adsorber?
A. When outlet concentration starts to rise
As the mass transfer zone reaches the outlet, pollutant appears in the effluent and the bed must be regenerated.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
Why are biofilters suited to treating odours from composting and livestock buildings?
D. Microbes cheaply degrade dilute soluble odorants
Moist media host microbes that oxidise compounds such as H2S, ammonia and VFAs at low cost for large dilute flows.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
In wet limestone flue gas desulphurisation, the main by-product is
B. gypsum, calcium sulphate
SO2 reacts with limestone and is oxidised to gypsum, usable in wallboard and cement.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
With a 3 dB exchange rate and a limit of 85 dB(A) for 8 hours, how long may a worker be exposed to 91 dB(A)?
D. 2 hours
Each 3 dB halves the time: 88 dB → 4 h, 91 dB → 2 h.
Further reading: See the manual sources: de Nevers; Cooper & Alley; CPCB NAAQS and AQI; WHO 2021 AQG; Noise Rules 2000
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