Question 1

Supersonic transport aircraft emissions: primary atmospheric region affected
Exhaust plumes from supersonic transport aircraft predominantly impact which atmospheric layer with respect to pollution and ozone chemistry?

Accepted Answer

Introduction / Context: High-altitude aviation emissions can perturb atmospheric chemistry beyond the surface layer. Supersonic transports (SSTs) cruise at altitudes overlapping the lower stratosphere, where ozone formation and destruction cycles are sensitive to NOx and other exhaust species. Given Data / Assumptions: SST cruise altitudes often approach or enter the lower stratosphere. Emissions include NOx, H₂O vapour, particles, and trace species. Concept / Approach: The stratosphere contains the ozone layer. Injected NOx catalytically converts ozone to O₂, and added water vapour can influence polar stratospheric cloud chemistry. Because vertical mixing is slower than in the troposphere, residence times and impacts can be significant relative to emission mass. Step-by-Step Solution: Map SST cruise regimes to atmospheric layers: lower stratosphere.Relate primary concern: ozone depletion chemistry and radiative effects.Select the stratosphere. Verification / Alternative check: Studies of historical SST concepts (e.g., Concorde) focused on stratospheric NOx and ozone impacts, not tropospheric air quality. Why Other Options Are Wrong: Troposphere: Commercial subsonic aircraft cruise mostly here; SST concerns center higher up.Thermosphere and mesosphere: Much higher altitudes than typical aircraft operations. Common Pitfalls: Assuming all aircraft emissions primarily affect ground-level air quality; altitude matters for chemistry and lifetimes. Final Answer: stratosphere

Question 2

Pick the incorrect statement about CO control and sources in ambient air
Identify the wrong assertion concerning catalytic converters, CO toxicity, petrol exhaust composition, and natural CO sources.

Accepted Answer

Introduction / Context: Automotive emissions and atmospheric carbon monoxide (CO) have well-documented sources and controls. This question checks familiarity with what three-way catalytic converters target, CO health effects, typical petrol exhaust composition, and natural background sources of CO. Given Data / Assumptions: Modern gasoline vehicles use catalytic converters to reduce CO, HC, and NOx. CO is toxic because it binds to hemoglobin, impairing oxygen transport. Petrol (gasoline) has low sulphur content, especially with modern fuel standards. Concept / Approach: Among the options, the incorrect claim is that SO₂ is the main pollutant in petrol exhaust. The dominant pollutants are CO, unburned hydrocarbons, and NOx; SO₂ is typically minor due to low sulphur levels in gasoline. The other statements are correct: catalytic converters reduce CO; CO can cause fatal asphyxiation; and biogenic/photochemical processes (including oxidation of organics) contribute to background CO. Step-by-Step Solution: Evaluate each statement against emissions science.Confirm the false one: SO₂ is not a main petrol exhaust pollutant. Verification / Alternative check: Emission standards and inventories consistently list CO and HC as the primary gasoline-exhaust concerns; SO₂ emissions primarily track fuel sulphur content and are far lower for petrol than for high-sulphur fuels. Why Other Options Are Wrong: (a) Correct: Catalysts oxidize CO to CO₂.(b) Correct: CO causes hypoxia by forming carboxyhemoglobin.(d) Correct: Natural processes can generate CO (e.g., oxidation of biogenic VOCs, biomass decay). Common Pitfalls: Assuming SO₂ is major across all fuels; it depends strongly on sulphur content, which is tightly limited in gasoline. Final Answer: Sulphur dioxide is the main pollutant emitted from the exhaust of petrol driven automobiles.

Question 3

Health outcomes of exposure to carcinogenic chemicals
When people are exposed to chemicals with carcinogenic properties, what is the principal long-term health risk?

Accepted Answer

Introduction / Context: Environmental and occupational health regulations classify substances by hazard class. Carcinogens are agents that increase the incidence of malignant tumors or cancer-related mortality. Recognizing this specific risk differentiates them from irritants, asphyxiants, sensitizers, and other toxicants. Given Data / Assumptions: “Carcinogenic” refers to established or suspected ability to cause cancer. Exposure scenarios can be inhalation, ingestion, dermal, or combined. Concept / Approach: Carcinogenesis involves DNA damage, mutagenesis, or epigenetic changes that lead to uncontrolled cell growth. While a carcinogen may also cause acute irritation or dermatitis, its defining hazard is increased cancer risk, often with latency periods of years or decades. Step-by-Step Solution: Match hazard class to health outcome: “carcinogenic” → “cancer.”Exclude acute outcomes that do not define carcinogenicity (asphyxiation, asthma, dermatitis). Verification / Alternative check: Regulatory lists (IARC, EPA, REACH) explicitly tie “carcinogen” designation to cancer risk, not to other endpoints. Why Other Options Are Wrong: Dermatitis: Characteristic of irritants or sensitizers, not the defining trait of carcinogens.Asphyxiation: Related to oxygen displacement or CO exposure, not carcinogenicity.Asthma: Result of respiratory sensitizers or irritants. Common Pitfalls: Confusing “toxic” with “carcinogenic.” Toxicity is broad; carcinogenicity is a specific chronic endpoint. Final Answer: cancer

Question 4

Volatile organics in municipal sewers: principal hazard
If volatile compounds such as gasoline, oil fractions, alcohols, or ether enter municipal sewers, what is the foremost immediate risk to the system and workers?

Accepted Answer

Introduction / Context: Sanitary sewers are confined spaces with limited ventilation. Introducing volatile organic compounds (VOCs) such as gasoline, ether, or alcohols can create flammable vapor mixtures that pose grave safety hazards to workers, the public, and infrastructure. Given Data / Assumptions: Presence of low-boiling, volatile, flammable substances in sewer headspace. Potential ignition sources (sparks, electrical equipment, static discharge) exist. Confined space with pockets where vapors can accumulate above lower explosive limit (LEL). Concept / Approach: VOCs readily evaporate and can form combustible mixtures with air. In confined spaces, even small releases may accumulate and migrate. The most acute hazard is explosion and fire, which can occur before chronic effects (e.g., corrosion) become significant. This is why industrial pretreatment programs strictly prohibit discharge of flammables into sanitary systems. Step-by-Step Solution: Recognize chemical properties: high vapor pressure + flammability.Confined environment → vapor pockets near LEL/UEL.Outcome: ignition → explosion risk. Verification / Alternative check: Incident case histories document manhole explosions and fires following gasoline or solvent discharges. Sewer entry protocols require LEL monitoring precisely for this reason. Why Other Options Are Wrong: Non biodegradable foam: Possible with surfactant discharges, but not the primary risk for the listed volatile solvents.Undesirable plant growth: Linked to nutrient releases, not VOCs in enclosed sewers.Corrosion: Some organics can contribute indirectly over time, but the immediate hazard from VOCs is explosion, not corrosion. Common Pitfalls: Underestimating ignition sources; even routine maintenance equipment can ignite vapor-air mixtures if not intrinsically safe. Final Answer: explosion

Question 5

Aquatic toxicity in environmental engineering
Which constituents in a water stream are particularly harmful (deleterious) to aquatic life and therefore must be controlled in wastewater treatment?

Accepted Answer

Introduction / Context: Protecting aquatic life is a central objective of environmental engineering. Different classes of pollutants stress fish and invertebrates in distinct ways. This question checks recognition of the main harmful groups commonly encountered in industrial and municipal effluents. Given Data / Assumptions: A water stream may carry dissolved organics, suspended solids, and toxic inorganics. We are concerned with ecological effects on fish, macroinvertebrates, and overall aquatic health. No special receiving-water dilution is assumed; impacts are considered at typical concentrations of concern. Concept / Approach: Deleterious effects arise via toxicity, oxygen depletion, habitat alteration, and bioaccumulation. Soluble toxic organics can be acutely or chronically toxic. Suspended solids reduce light penetration, clog gills, smother eggs, and carry attached toxics. Heavy metals and cyanides are well-known acute toxins; metals can bioaccumulate and cause long-term sublethal effects. Step-by-Step Solution: Identify toxic organics: many solvents, phenolics, and surfactants harm fish at low mg/L.Evaluate suspended solids: increase turbidity, deposit as silt, and impair respiration and spawning grounds.Consider metals and cyanides: cause acute toxicity, neurological effects, and enzyme inhibition.Integrate impacts: each category can independently harm aquatic life, so all listed groups are deleterious. Verification / Alternative check: Regulatory frameworks (e.g., limits on BOD, TSS, metals, and CN) reflect these risks. Biological monitoring (fish kills, macroinvertebrate indices) correlates spikes in any of these pollutants with ecological damage. Why Other Options Are Wrong: Soluble and toxic organics only: Ignores physical smothering by solids and acute heavy metal/cyanide toxicity.Suspended solids only: Omits chemical toxicity mechanisms.Heavy metals and cyanides only: Omits organic toxicity and solids-induced stress. Common Pitfalls: Assuming only “toxicity” matters; in reality, non-toxic solids still damage aquatic habitats. Also, some pollutants bind to solids, compounding effects. Final Answer: all (a), (b) & (c).

Question 6

Automobile emissions — identify the principal pollutant in exhaust
In the context of typical petrol/gasoline engine exhaust without after-treatment, which pollutant is the dominant concern?

Accepted Answer

Introduction / Context: Road vehicles emit a mixture of pollutants. Historically, before widespread catalytic converters and stringent standards, one compound dominated public-health concerns from gasoline engines: carbon monoxide (CO). Given Data / Assumptions: Spark-ignition engines operating near stoichiometric conditions without advanced after-treatment. Question asks for the main pollutant by concern and typical prominence in raw exhaust. Diesel engines differ; focus here is gasoline-type exhaust. Concept / Approach: CO forms from incomplete combustion of carbon in fuel. In spark-ignition engines, CO fractions in raw exhaust are relatively high compared with many other toxic components. CO is colorless, odorless, and interferes with oxygen transport in blood, making it a critical pollutant historically targeted by automotive catalysts. Step-by-Step Solution: Compare pollutants: CO vs CO2 vs NO vs hydrocarbons.CO2 is a greenhouse gas but not a toxic “pollutant” in the same acute sense at tailpipe levels.NO is a component of NOx, significant but typically controlled with three-way catalysts; raw SI exhaust still has more CO by mass.Unburned hydrocarbons are important for smog but often lower than CO in raw SI exhaust streams. Verification / Alternative check: Emission inventories and textbook data show high CO percentages in untreated gasoline engine exhaust, validating CO as the principal pollutant historically addressed. Why Other Options Are Wrong: CO2: A climate pollutant, but not the principal toxic exhaust pollutant targeted by local air-quality standards.NO: Part of NOx; important but usually less dominant than CO in untreated SI exhaust.Hydrocarbons: Contribute to ozone and photochemical smog, yet CO typically predominates by mass in raw gasoline exhaust. Common Pitfalls: Confusing climate relevance (CO2) with acute toxicity (CO), and conflating diesel vs gasoline emission profiles. Final Answer: CO

Question 7

Decolourisation of printing industry effluent
Which treatment method is most commonly applied to remove color from dye-rich printing wastewaters in practice?

Accepted Answer

Introduction / Context: Printing and dyeing effluents often contain chromophores that resist biodegradation and impart intense color. Removing color is crucial for meeting discharge standards and for downstream reuse or polishing. Given Data / Assumptions: Wastewater contains soluble dyes and color bodies. Objective is practical, scalable decolourisation. Cost, robustness, and selectivity matter in plant operations. Concept / Approach: Adsorption, especially with activated carbon, is a widely used polishing step because it targets a broad spectrum of organic color-causing molecules, is modular, and integrates easily after biological treatment. Alternatives like reverse osmosis can remove color but at higher energy and with concentrate disposal issues, and ion exchange tends to be selective, less cost-effective for complex dye mixtures. Electrochemical methods may help but are less common at large scale for printing effluents. Step-by-Step Solution: Identify the nature of pollutants: high-molecular-weight organics with chromophores.Map to treatment options: adsorption onto high surface area carbon is versatile.Consider operability: GAC columns or PAC dosing offer controllable performance.Select adsorption as the most common and practical decolourisation step. Verification / Alternative check: Plant case studies show activated carbon following secondary treatment consistently lowers color and COD; lab jar tests confirm rapid color uptake on carbon. Why Other Options Are Wrong: Ion exchange: Works for specific ionic species; dyes are diverse and often weakly ionized or bulky.Reverse osmosis: Effective but energy-intensive with brine disposal challenges.Electrolytic decomposition: Niche and variable in economics for complex dye mixtures. Common Pitfalls: Relying solely on biological treatment; many dyes are recalcitrant and require a polishing step like adsorption. Final Answer: adsorption.

Question 8

Typical dissolved oxygen (DO) in river water
In a healthy, well-aerated river reach, the dissolved oxygen concentration is commonly around how many parts per million (ppm)?

Accepted Answer

Introduction / Context: Dissolved oxygen (DO) is a core indicator of aquatic ecosystem health. Adequate DO supports fish respiration, aerobic biodegradation, and overall riverine biodiversity. Given Data / Assumptions: We consider typical temperate conditions with moderate temperature. Values are in ppm, interchangeable with mg/L for dilute aqueous solutions. Water is not supersaturated and is free from extreme organic loading. Concept / Approach: Oxygen solubility in water at ambient conditions is on the order of single-digit mg/L. Natural rivers often have DO around 5 to 9 mg/L depending on temperature, turbulence, and biological activity. Values in the hundreds of ppm are physically unrealistic for oxygen solubility at normal pressure. Step-by-Step Solution: Recall oxygen solubility at 20°C ~ 9 mg/L; warmer water holds less.Healthy river reaches typically maintain > 5 mg/L to avoid fish stress.Among the options, 5 ppm is the only realistic magnitude. Verification / Alternative check: Field measurements and standards (often DO > 5 mg/L for aquatic life) align with this range; environmental guidelines use similar thresholds. Why Other Options Are Wrong: 100, 250, 500 ppm are orders of magnitude above oxygen solubility at 1 atm and cannot occur in natural rivers. Common Pitfalls: Confusing DO with BOD or COD values that may be larger, and misinterpreting ppm scales across different pollutants. Final Answer: 5

Question 9

Nuclear accident history — identify the worst radioactive pollution event
The world’s worst radioactive pollution from a nuclear reactor disaster occurred at which location?

Accepted Answer

Introduction / Context: Understanding major environmental disasters helps frame modern safety standards and risk management. The worst nuclear-power-related radioactive release in history is a well-known landmark event. Given Data / Assumptions: Comparing famous incidents: Chernobyl (1986), Three Mile Island in Pennsylvania (1979), and others. Metric is overall radioactive pollution and environmental impact. Concept / Approach: The Chernobyl Unit 4 accident in the then U.S.S.R. (now Ukraine) involved a catastrophic power excursion and steam explosion followed by a graphite fire, ejecting large quantities of radionuclides into the atmosphere, contaminating broad regions and prompting long-term exclusion zones. Step-by-Step Solution: List candidate sites and incidents.Assess scale: Chernobyl had widespread fallout and long-term contamination far exceeding that of other listed events.Select Chernobyl (undivided U.S.S.R.) as the correct location. Verification / Alternative check: International assessments (e.g., UNSCEAR and IAEA reports) document the magnitude of releases and health/environmental consequences, confirming Chernobyl’s severity. Why Other Options Are Wrong: Arizona (U.S.A.) / Moscow (U.S.S.R.): No reactor disasters there of comparable scale.Pennsylvania: Three Mile Island was serious but had far smaller releases than Chernobyl. Common Pitfalls: Confusing nuclear weapons tests or other incidents with civilian reactor accidents. Final Answer: Chernobyl (undivided U.S.S.R.)

Question 10

Occupational health in leather tanning and manufacture
Workers in leather tanning and related manufacturing are especially prone to which health problem due to process exposures?

Accepted Answer

Introduction / Context: Industrial hygiene identifies hazard–exposure–outcome pathways. Leather tanning and finishing involve chemicals that can irritate or sensitize the skin, making dermatologic disorders a notable risk for workers. Given Data / Assumptions: Exposure to chromium salts (particularly Cr(III) compounds) and other tanning/finishing chemicals. Wet processes with repeated skin contact potential. Limited respiratory dust exposure compared to mining or foundry work. Concept / Approach: Contact dermatitis (irritant and allergic) is common in tanneries due to chromium, dyes, and finishing agents. Appropriate personal protective equipment (PPE), process containment, and hygiene practices reduce incidence, but skin disorders remain the characteristic occupational health issue in this sector. Step-by-Step Solution: Consider exposure profile: frequent skin contact with tanning solutions and finishing chemicals.Link exposure to outcome: dermatitis and other skin diseases are well documented.Select skin diseases (dermatitis) as the primary concern. Verification / Alternative check: Occupational health literature reports elevated dermatitis cases in tanneries; safety data sheets flag skin irritation/sensitization risks. Why Other Options Are Wrong: Respiratory ailments/blurred vision: Possible but not the defining risk of tanning operations.Silicosis: Associated with respirable crystalline silica, typical in mining/stonework, not core to tanning. Common Pitfalls: Underestimating allergic dermatitis; even low exposures can trigger sensitization over time. Final Answer: skin diseases (e.g. dermatitis).

Question 11

Occupational noise — 8-hour exposure limit in a chemical plant
What is the commonly accepted maximum allowable continuous noise level for an 8-hour workday (time-weighted), expressed in decibels?

Accepted Answer

Introduction / Context: Noise exposure standards protect workers from hearing loss. Many jurisdictions adopt or align with guidelines that specify an 8-hour permissible exposure limit (PEL) near 90 dB(A), with exchange rates for higher levels at shorter durations. Given Data / Assumptions: Continuous noise exposure over an 8-hour shift. A-weighted decibels are implied (dB(A)). Standard industrial environment in a chemical plant. Concept / Approach: As exposure time increases, allowable noise level decreases, and vice versa. A traditional baseline PEL is 90 dB(A) for 8 hours. Many best-practice programs target 85 dB(A) for hearing conservation, but the question asks for the commonly accepted “maximum allowable” level, which is typically cited as about 90 dB(A). Step-by-Step Solution: Identify the 8-hour criterion: the standard reference duration.Recall PEL: approximately 90 dB(A) for 8 hours in many regulatory schemes.Choose 90 dB as the closest option. Verification / Alternative check: Occupational guidelines and hearing conservation literature consistently reference 90 dB(A) for 8 hours as a limit, with action levels around 85 dB(A). Why Other Options Are Wrong: 20 and 60 dB are too low for industrial limits; 120 dB is far above safe continuous exposure for 8 hours. Common Pitfalls: Confusing action levels (e.g., 85 dB(A)) with maximum allowable limits for an 8-hour TWA. Final Answer: 90

Question 12

Typical noise levels in public transport environments
The sound level inside a city bus in heavy traffic or inside a subway/train car is typically around how many decibels?

Accepted Answer

Introduction / Context: Urban noise exposure often occurs during commuting. Recognizing typical levels helps in assessing daily noise dose relative to occupational or environmental guidelines. Given Data / Assumptions: Busy city traffic or inside a subway car. Short-term peaks can occur, but we consider a representative level. A-weighted decibels are implied. Concept / Approach: Typical interior levels in buses and subway cars can range from roughly 85 to 100 dB(A) depending on vehicle condition, speed, and crowding. A mid-high value around 95 dB is often cited for noisier conditions and matches the upper typical range of such environments. Step-by-Step Solution: Assess realistic ranges: 75 dB is common for quieter offices/streets, lower than typical subway interiors.Consider peaks and averages: congested, braking, track noise can push toward 90–100 dB.Select 95 dB as the best representative among the choices. Verification / Alternative check: Field measurements reported by urban acoustic surveys frequently find 90+ dB inside older subway cars or crowded buses during peak conditions. Why Other Options Are Wrong: 120 and 140 dB are extreme levels associated with jet engines or gunshots, not routine public transport interiors; 75 dB is too low for the stated scenarios. Common Pitfalls: Confusing indoor public spaces (often 60–70 dB) with amplified transit environments that include mechanical and structural noise sources. Final Answer: 95

Question 13

Industrial sources of NOx — identify where it is not produced
Among the following industries, where is nitrogen oxides (NOx) not a typical process emission?

Accepted Answer

Introduction / Context: Nitrogen oxides (NO and NO2, collectively NOx) are produced in high-temperature combustion and in specific nitrogen-processing chemical operations. Identifying typical sources is fundamental to air-pollution control planning. Given Data / Assumptions: Nitric acid manufacture intentionally oxidizes ammonia, forming NOx intermediates. Nitrogenous fertilizer production often integrates nitric acid or ammonia oxidation steps. Detergent manufacturing primarily involves surfactant chemistry without NOx-forming oxidation stages. Concept / Approach: NOx is an intrinsic by-product in nitric acid plants (e.g., tail gas) and can be associated with fertilizer processes that use or make nitric acid. In contrast, detergent plants are not primary NOx process sources, aside from general combustion emissions (e.g., steam boilers), which are not the core process emissions the question targets. Step-by-Step Solution: Map each industry to its core chemistry.Recognize nitric acid and related fertilizer processes as NOx emitters.Identify detergent manufacture as not producing NOx in the main process stream. Verification / Alternative check: Emission inventories list nitric acid plants as classic NOx sources; detergent plants typically control VOCs and particulate from powders, not NOx process emissions. Why Other Options Are Wrong: Nitric acid making / nitrogenous fertiliser: Both have NOx in process gases.Any of these: Incorrect because detergent manufacture does not inherently produce NOx as a process stream. Common Pitfalls: Confusing general utility boilers (which can emit NOx) with the core chemical process emissions referenced in such questions. Final Answer: detergent

Question 14

Photochemical smog components — source of PAN
Peroxyacyl nitrates (PAN) are secondary pollutants typically found where?

Accepted Answer

Introduction / Context: Peroxyacyl nitrates (PAN) are eye-irritating components of photochemical smog formed by reactions of nitrogen oxides (NOx) with volatile organic compounds (VOCs) under sunlight. Urban traffic emissions provide the precursor mix that leads to PAN formation. Given Data / Assumptions: Automobiles emit NOx and hydrocarbons (VOCs). PAN is not a primary pollutant; it forms in the atmosphere from precursors. Coal power and acid plants have different dominant pollutants (SOx, NOx) but not the VOC mix and conditions that favor PAN at the source. Concept / Approach: Photochemical smog requires sunlight, NOx, and reactive hydrocarbons. Urban road traffic supplies both NOx and VOCs; in sunlight, radical chemistry generates PAN and ozone. Industrial stacks may emit NOx or SOx but generally lack high VOC co-emissions and immediate photochemical conditions at the stack exit to create PAN right there. Step-by-Step Solution: Identify precursors: VOCs + NOx + sunlight.Map sources: vehicle exhausts supply VOCs and NOx in dense urban canyons.Conclude PAN is associated with automobile exhaust and urban smog episodes. Verification / Alternative check: Air-quality monitoring in cities shows PAN peaks during sunny traffic periods, co-varying with ozone and NOx–VOC photochemistry. Why Other Options Are Wrong: Coal power flue gas: Dominated by SOx and NOx; limited VOCs; PAN formation occurs downwind only if VOCs are present.Nitric/sulphuric acid plants: Emissions focus on NOx or SOx; PAN is not a direct plant exhaust constituent. Common Pitfalls: Treating PAN as a primary pollutant; it is a secondary pollutant formed in the urban atmosphere. Final Answer: automobile exhaust.

Question 15

CO2 hazard threshold in ambient air
At approximately what concentration of carbon dioxide in atmospheric air (percent by volume) does an acute danger to human life exist, with a high likelihood of rapid loss of consciousness and death if exposure c…

Accepted Answer

Introduction / Context: Understanding toxicological thresholds for common gases is essential in environmental engineering and industrial safety. Carbon dioxide (CO2), although not toxic in the same way as carbon monoxide, becomes dangerously asphyxiating at high concentrations by displacing oxygen and depressing the respiratory drive. This question asks for the approximate concentration in air at which CO2 poses an acute, life-threatening danger. Given Data / Assumptions: Ambient air baseline CO2 is roughly 0.04% (400 ppm). Exposure is short-term, acute (minutes), not chronic. No supplemental breathing apparatus; normal atmospheric pressure. Concept / Approach: CO2 is an asphyxiant. As concentration rises, the partial pressure of oxygen in the inhaled air falls and CO2 directly stimulates chemoreceptors, causing hyperventilation, headache, and eventually narcosis. Typical guidance values: 1–2% causes mild symptoms, 3–5% pronounced distress, 7–10% severe dizziness and unconsciousness, and near 20% rapid loss of consciousness with a high probability of death without immediate rescue. Therefore, the threshold of “acute danger to human life” is most closely represented by about 20%. Step-by-Step Solution: Recognise that the question targets a lethal, not merely symptomatic, concentration.Recall severity bands: 1–3% discomfort, 7% extreme symptoms, 20% swiftly fatal.Select the option that corresponds to an unambiguous, immediate life-threatening range: 20%. Verification / Alternative check: Safety datasheets and industrial hygiene references classify 20% CO2 as an atmosphere rapidly fatal to unprotected personnel due to combined oxygen displacement and hypercapnia. Why Other Options Are Wrong: 1%: Generally causes mild symptoms only. 3%: Distressing but not typically immediately lethal. 7%: Severe effects and loss of consciousness can occur, but the phrase “acute danger to human life (death)” is more definitively associated with ~20%. 12%: Highly dangerous but not provided in the original set; 20% better matches the “immediate death” framing. Common Pitfalls: Confusing occupational exposure limits (long-term) with acute lethality thresholds; mixing up CO2 (asphyxiant) with CO (chemical hypoxia). Final Answer: 20

Question 16

Thermal pollution and toxicity amplification
A 10°C rise in receiving water temperature can double the toxic effects of which contaminant commonly discussed in environmental toxicology?

Accepted Answer

Introduction / Context: Thermal pollution occurs when heated effluents elevate the temperature of natural waters. Temperature influences chemical speciation, volatilisation, metabolic rates of aquatic organisms, and toxicity of dissolved pollutants. Engineers must anticipate how a heat load can magnify toxic impacts even when concentrations remain unchanged. Given Data / Assumptions: Receiving water temperature rises by roughly 10°C due to a discharge. Toxic effects are evaluated at comparable pH and oxygen conditions. Focus is on the relative change in toxicity with temperature, not absolute lethal doses. Concept / Approach: For weak acids/bases and certain inorganic species, temperature shifts alter dissociation equilibria and biological uptake. Cyanides, especially potassium cyanide in water, can form undissociated hydrogen cyanide (HCN). As temperature rises, the fraction of HCN in equilibrium increases and its volatility and membrane permeability increase, enhancing toxicity to aquatic life. Empirical observations and classical environmental texts note that a 10°C increase can roughly double the toxic effects of cyanides under comparable conditions. Step-by-Step Solution: Identify pollutants with toxicity highly sensitive to temperature and speciation.Recognise cyanide systems (CN⁻/HCN) shift toward more bioavailable/volatile HCN at higher temperature.Conclude that potassium cyanide exhibits approximately doubled toxicity with a 10°C rise. Verification / Alternative check: Acute LC50 values for fish and invertebrates show stronger toxicity at elevated temperatures for cyanide-bearing waters, consistent with increased HCN fraction. Why Other Options Are Wrong: Coal ash: Suspended solids and trace metals are temperature-influenced, but not typically described by a “doubling per 10°C.” Ortho-xylene: Organic solvent toxicity is less governed by a simple 10°C doubling rule. None of these: Incorrect because cyanide is the classic example. Chromium(VI) salts: Highly toxic but not characterised by this specific temperature doubling heuristic. Common Pitfalls: Assuming all toxicants respond similarly to temperature; ignoring speciation and bioavailability changes unique to cyanide chemistry. Final Answer: Potassium cyanide

Question 17

Noise abatement by green belts
By approximately how many decibels can planting dense tree belts (e.g., coconut, neem) near hospitals and schools reduce ambient noise levels under practical conditions?

Accepted Answer

Introduction / Context: Green belts act as physical and psychological buffers against urban noise. Vegetation can scatter, absorb, and block sound, though its effect depends on belt width, foliage density, frequency spectrum of noise, and ground conditions. Urban planners commonly deploy trees and shrubs near sensitive receptors such as hospitals and schools to mitigate noise nuisance. Given Data / Assumptions: Moderate-width belts with mixed species and full foliage. Noise sources include road traffic and typical urban activities. Measurement positions are just behind the vegetative barrier relative to the source. Concept / Approach: Vegetation reduces sound primarily by high-frequency scattering and some absorption; low-frequency traffic noise penetrates more easily. Practical guidance suggests that well-designed belts (10–30 m wide, dense undergrowth) achieve reductions around 5–10 dB at receiver locations close to the barrier, with diminishing returns beyond certain widths or in the presence of gaps. Step-by-Step Solution: Identify typical reduction capabilities from environmental acoustics references.Account for frequency content of urban noise and realistic belt designs.Select 5–10 dB as the commonly achievable attenuation by tree planting alone. Verification / Alternative check: Field studies and standards handbooks report 5–10 dB(A) attenuation for dense plantings; higher claims usually require engineered barriers (e.g., walls, earth berms). Why Other Options Are Wrong: 1–2 dB: Too small for dense green belts. 15–20 dB or 25–30 dB: Typically require solid barriers or substantial berms. 35–40 dB: Unrealistic for vegetation alone. Common Pitfalls: Overestimating tree-only performance; ignoring gaps or seasonal leaf loss which reduce effectiveness. Final Answer: 5-10

Question 18

Drinking water hygiene
What is the principal public health concern associated with the presence of bacteria in potable (drinking) water supplies?

Accepted Answer

Introduction / Context: Safe drinking water is defined primarily by its microbiological quality. While aesthetic parameters such as taste, odour, and colour are important to consumers, regulatory frameworks focus foremost on eliminating pathogenic microorganisms that cause waterborne diseases like cholera, typhoid, and dysentery. Given Data / Assumptions: Potable water refers to treated water entering distribution systems. “Presence of bacteria” means potential presence of pathogens or indicator organisms (e.g., coliforms). Aesthetic issues are secondary to health protection. Concept / Approach: Human pathogens transmitted via water include bacteria, viruses, and protozoa. Even when turbidity and odour are acceptable, the presence of pathogenic bacteria can cause outbreaks. Therefore, disinfection (e.g., chlorination, UV) and barriers (coagulation, filtration) target microbial safety first. Indicator tests (total coliforms, E. coli) serve as proxies for pathogen intrusion. Step-by-Step Solution: Identify the most severe consequence of bacterial contamination: infectious disease.Recall that regulatory standards often require zero detectable E. coli in routine samples.Conclude that “Disease” is the principal concern among the options. Verification / Alternative check: Epidemiological data link bacterial contamination to gastrointestinal illness; WHO and national standards emphasise pathogen removal and residual disinfectant maintenance. Why Other Options Are Wrong: Turbidity / Bad odour / Bad taste and colour: Important but primarily aesthetic; they can accompany contamination but are not the core health risk. Scaling of pipes: A water chemistry issue, not directly related to bacterial presence. Common Pitfalls: Equating clear water with safe water; pathogens can be present even when appearance and odour are acceptable. Final Answer: Disease

Question 19

Identifying particulate air pollutants
“Particulate” air pollutants comprise finely divided solids or liquids suspended in air. Which of the following is not a particulate class when stated as a pair?

Accepted Answer

Introduction / Context: Air pollutants are often grouped by physical form: gases/vapours and particulates (solids or liquid droplets). Correct classification matters for selecting control technologies (e.g., cyclones, fabric filters for particulates; scrubbers or catalysts for gases). This item checks understanding of typical particulate categories and a notable exception. Given Data / Assumptions: Particulates include dust, smoke, fumes, mist, aerosol, and soot (black carbon). Photochemical smog is a complex gaseous mixture formed by sunlight-driven reactions (e.g., ozone, peroxyacyl nitrates) with some aerosol contribution. The options are presented as pairs. Concept / Approach: Dust (solid), smoke/fumes (very fine solids from combustion/condensation), mists/fog (liquid droplets), and soot (solid carbon) are particulate forms. Photochemical smog, however, is primarily a gaseous-phase pollution episode with oxidants like ozone, although it can include aerosols secondarily. As a pair, “photochemical smog and soot” mixes a non-particulate class (smog) with a particulate (soot), making the pair not purely particulate. Step-by-Step Solution: List each term’s physical state: dust/ smoke/ fumes/ mist/ soot are particulate; photochemical smog is largely gaseous oxidants.Identify the pair that fails to represent two particulate classes.Select “Photochemical smog and soot.” Verification / Alternative check: Air quality textbooks define photochemical smog by ozone and NOx-VOC chemistry, not particulate identity, confirming the mismatch in the pair. Why Other Options Are Wrong: Dust and mists / Smoke and fumes: Both terms in each pair are particulate categories. None of these: Incorrect because option (c) contains a non-particulate term. Fog and haze: Both are aerosols (liquid and mixed-phase particulates), fitting particulate classes. Common Pitfalls: Thinking “smog” equals particulate matter only; photochemical smog is dominated by gaseous oxidants with secondary aerosols. Final Answer: Photochemical smog and soot

Question 20

Water vapour in the troposphere
Depending on altitude and temperature, the concentration of water vapour in the troposphere varies from essentially zero up to about what percent (by volume)?

Accepted Answer

Introduction / Context: Water vapour is the most variable greenhouse gas in the lower atmosphere. Its concentration controls humidity, cloud formation, and atmospheric stability. Environmental engineers need a sense of its typical bounds to reason about condensation, fogging, and the behaviour of pollutants and aerosols. Given Data / Assumptions: Troposphere conditions (surface to tropopause). Cold, high-altitude air can be extremely dry; near-surface tropical air can be very humid. Values are approximate volumetric percentages. Concept / Approach: Near the surface in warm, humid climates, water vapour commonly reaches several percent by volume; over deserts and at high altitudes, it approaches zero. A widely cited envelope is 0–4% by volume in the troposphere. Hence, the upper bound asked in the question is about 4%. Step-by-Step Solution: Recall the typical global range of tropospheric humidity by volume fraction.Note that 4% is the conventional upper limit in warm, moist air masses.Select 4% as the correct maximum in the provided options. Verification / Alternative check: Meteorological references consistently quote 0–4% by volume for tropospheric water vapour, depending on weather and geography. Why Other Options Are Wrong: 1% or 2%: Too low for humid tropical air. 8% or 12%: Exceed typical observed atmospheric limits. Common Pitfalls: Confusing relative humidity (%) with absolute volumetric fraction; these are related but not the same measure. Final Answer: 4

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