Question 1

Structure of the atmosphere — identify the lowest layer
What is the name of the lowest layer of Earth’s atmosphere, where weather phenomena and human activities predominantly occur?

Accepted Answer

Introduction / Context: The atmosphere is stratified into layers with distinct temperature gradients and compositions. Recognizing these layers is foundational in environmental engineering, meteorology, and pollution dispersion modeling. Given Data / Assumptions: The layers (from surface upward) are troposphere, stratosphere, mesosphere, thermosphere (which includes the ionosphere), and exosphere. We are asked to identify the lowest layer adjacent to Earth’s surface. Concept / Approach: The troposphere extends from the surface to roughly 8–18 km, depending on latitude and season. It contains most atmospheric mass and nearly all water vapor, supporting clouds, precipitation, winds, and day-to-day weather. Temperature generally decreases with altitude in this layer. Step-by-Step Solution: List layers in order from surface: troposphere → stratosphere → mesosphere → thermosphere.Note key feature: weather occurs in the troposphere due to water vapor content and convection.Select “troposphere” as the lowest atmospheric layer. Verification / Alternative check: Weather forecasting, air quality models, and aircraft flight levels confirm that the operational weather layer is the troposphere capped by the tropopause. Why Other Options Are Wrong: Stratosphere: Lies above the troposphere and contains the ozone layer; limited vertical mixing.Ionosphere: A region of ionization within the thermosphere; not the lowest layer.None of these: Incorrect because the troposphere is listed. Common Pitfalls: Confusing the ozone-rich stratosphere with the lowest layer; while crucial for UV shielding, it is not the layer at the surface. Final Answer: troposphere

Question 2

Global warming driver — principal cause of progressive surface warming
The progressive warming of Earth’s surface is mainly attributed to which factor?

Accepted Answer

Introduction / Context: Global warming refers to the long-term upward trend in Earth’s average surface temperature. Understanding the primary driver is essential for environmental management and policy. Given Data / Assumptions: We compare several environmental issues and sources. The question targets the main physical mechanism, not just specific sources. Concept / Approach: Carbon dioxide and other greenhouse gases absorb outgoing longwave (infrared) radiation and re-emit it, creating a “blanketing” effect that warms the lower atmosphere and surface. While many activities (e.g., fossil fuel combustion, deforestation) influence concentrations, the greenhouse effect mechanism of CO2 is the central cause of progressive warming. Step-by-Step Solution: Link increased CO2 concentration to radiative forcing (positive).Recognize that automobile exhaust is a source of CO2 but is not the mechanism itself.Differentiate ozone layer issues from greenhouse warming.Select the blanketing effect of CO2 as the primary cause listed. Verification / Alternative check: Climate assessments attribute the majority of observed warming to anthropogenic greenhouse gases, with CO2 being the largest single contributor to radiative forcing. Why Other Options Are Wrong: Automobile exhaust: A source category, not the fundamental physical cause.De-forestation: Contributes by reducing CO2 sinks, but the option asked for the main cause; the greenhouse effect captures the mechanism directly.Thickening of ozone layer: Unrelated; ozone depletion and recovery are distinct from greenhouse warming. Common Pitfalls: Mixing sources with mechanisms; the correct answer emphasizes the physical greenhouse effect. Final Answer: blanketing effect of CO2 in the atmosphere.

Question 3

Measuring color in water analysis
In standard water-quality testing, which instrument is classically used to determine the apparent color of a water sample?

Accepted Answer

Introduction / Context: Color is an aesthetic and diagnostic parameter in drinking water and wastewater. Detecting and quantifying color helps identify dissolved organics, metals, and treatment issues. Given Data / Assumptions: The task is to identify the commonly named instrument for color comparison in water testing. Apparent color is evaluated visually against standardized color standards. Concept / Approach: A tintometer (e.g., Lovibond) is a visual comparator instrument that matches the color of a water sample against calibrated glass or plastic standards on a defined color scale. While modern spectrophotometric colorimeters exist, classic waterworks practice and many textbooks explicitly refer to the tintometer for routine color determination. Step-by-Step Solution: Recognize that “tintometer” is a dedicated visual comparator for color.Differentiate from “turbidimeter,” which measures light scattering by suspended particles (turbidity), not color.Note that a generic “colorimeter” usually refers to photoelectric absorbance devices; the traditional water color test cites a tintometer by name.Select tintometer as the expected answer. Verification / Alternative check: Standard methods in older waterworks manuals and exam keys associate color testing with the Lovibond tintometer procedure. Why Other Options Are Wrong: Colorimeter: Although usable, the classic instrument named in many curricula is the tintometer; the item asks for the instrument specifically associated with the color test.Electro-chemical cell: Used for conductivity, pH, or specific ion measurements, not color.Turbidimeter: Measures turbidity (NTU), not true/apparent color. Common Pitfalls: Confusing turbidity (suspended particles) with color (dissolved substances). Final Answer: tintometer

Question 4

Asphyxiant in air — toxicology threshold
Which pollutant causes death by asphyxiation if its concentration in atmospheric air exceeds the maximum allowable level (greater than about 50 ppm)?

Accepted Answer

Introduction / Context: Asphyxiants interfere with oxygen delivery to tissues. Recognizing the most dangerous low-level asphyxiant in urban air is essential for safety, environmental monitoring, and public health. Given Data / Assumptions: The threshold mentioned (~50 ppm) is an order-of-magnitude cue for acute concern. Candidates include carcinogens, oxidants, and a well-known hemoglobin-binding gas. Concept / Approach: Carbon monoxide (CO) binds hemoglobin with much higher affinity than oxygen, forming carboxyhemoglobin and reducing blood’s oxygen-carrying capacity. Even tens of ppm for prolonged exposure can cause symptoms; higher concentrations lead to loss of consciousness and death. The others listed are harmful but do not produce classic hemoglobin-related asphyxiation at such low ppm levels. Step-by-Step Solution: Identify the asphyxiation mechanism: hemoglobin binding → impaired oxygen transport.Match to pollutant: CO is the classic chemical asphyxiant at relatively low ppm.Eliminate alternatives: benzopyrene (carcinogen), PAN (photochemical irritant), SO2 (respiratory irritant).Select carbon monoxide as the correct answer. Verification / Alternative check: Toxicology references list exposure guidelines and health effects for CO, showing rapid onset of hypoxia symptoms as concentrations rise above tens to hundreds of ppm. Why Other Options Are Wrong: Benzopyrene: Polycyclic aromatic carcinogen; not an acute asphyxiant.Peroxyacyl nitrate: Eye/respiratory irritant in photochemical smog; not primarily asphyxiating.Sulphur dioxide: Potent irritant and bronchoconstrictor; asphyxiation is not its principal mode at 50 ppm. Common Pitfalls: Assuming any toxic gas at 50 ppm causes asphyxiation; the unique hemoglobin affinity of CO makes it particularly dangerous. Final Answer: Carbon monoxide

Question 5

Solid waste management terminology
The biological decomposition of organic substances in wastes under controlled conditions (temperature, moisture, aeration) is called:

Accepted Answer

Introduction / Context: In environmental engineering, different unit operations and processes are used to stabilise municipal solid waste and organic residues. When the goal is to convert putrescible matter into a stable, humus-like product using microorganisms under managed conditions, the process has a specific name that distinguishes it from burning, uncontrolled decay, or purely liquid-phase biodegradation. Knowing this term helps in selecting appropriate treatment technology and in designing facilities for cities and industries. Given Data / Assumptions: The waste contains biodegradable organics such as kitchen waste, yard trimmings, and agricultural residues. Conditions are controlled: moisture, temperature, aeration, and carbon to nitrogen ratio are adjusted. The target is a stable, soil-conditioner product rather than energy recovery by combustion. Concept / Approach: Biological stabilisation can be aerobic or anaerobic. Aerobic management with forced or natural aeration and active turning typically produces heat, accelerates microbial activity, and yields a finished compost. The process parameters include moisture around 50–60%, C/N ratio about 25–30, and pile temperatures that pass through mesophilic and thermophilic phases. This set of controlled, engineered steps is called composting. It differs fundamentally from incineration (thermal oxidation) and from generic “biological oxidation” which is a broad descriptor often used for wastewater treatment reactions. Step-by-Step Solution: Identify that the question specifies controlled conditions for organic waste decomposition.Recall the engineered process name used for aerobic degradation to a stable, humus-like product.Select the term that matches these features: composting. Verification / Alternative check: Design manuals for solid waste processing describe windrow, aerated static pile, and in-vessel composting systems, all emphasising control of air, moisture, and temperature to produce compost safely and efficiently. Why Other Options Are Wrong: Incineration: High-temperature combustion for volume reduction and energy, not biological decomposition. Biological oxidation: Too generic; not the specific engineered solid waste process name. None of these: Incorrect because a standard term exists. Anaerobic digestion: Biological but oxygen-free, produces biogas rather than compost as the main product. Common Pitfalls: Confusing any biodegradation with composting; ignoring the requirement for controlled aeration and management parameters. Final Answer: Composting

Question 6

Drinking water aesthetics – colour limit
What is the permissible colour for domestic water supply, expressed as ppm on the platinum–cobalt (Hazen) colour scale?

Accepted Answer

Introduction / Context: Besides safety, drinking water must meet aesthetic standards so that consumers accept it. Colour is an important aesthetic parameter caused by dissolved organics (humic substances), metals, or pipe corrosion products. Regulatory and guideline documents typically express colour using the platinum–cobalt (Pt–Co) or Hazen colour scale, historically reported as “ppm” or “true colour units.” Given Data / Assumptions: Domestic (potable) supply after conventional treatment. Colour reported on the Pt–Co (Hazen) scale in ppm units. Question targets a typical permissible limit used in practice and standards. Concept / Approach: Most drinking water standards and design manuals recommend that the true colour be low enough to be essentially unnoticeable. A widely cited threshold for acceptability is about 15–20 units on the Pt–Co scale, with many texts stating 20 ppm (Hazen units) as a practical upper limit for distribution systems. Thus, among the options offered, 20 ppm aligns with customary permissible levels for domestic supply aesthetics. Step-by-Step Solution: Recognise that the parameter is the Pt–Co (Hazen) colour scale.Recall typical guidance: colour should be less than or equal to about 20 units for consumer acceptability.Select 20 as the permissible value from the options. Verification / Alternative check: Water quality handbooks commonly reference 15 units as desirable and 20 units as a permissible level; utilities often design to keep colour comfortably below this ceiling. Why Other Options Are Wrong: 1 or 5: Very stringent; achievable, but the question asks the permissible limit, not the ideal. 100 or 1000: Excessive colour; visibly unacceptable to consumers. Common Pitfalls: Confusing “ppm” on the Pt–Co scale with mass concentration; Hazen units are based on a standard colour solution rather than direct mg/L of a specific compound. Final Answer: 20

Question 7

Oxidation pond design – detention time
In sewage treatment, the typical detention period provided for facultative oxidation ponds ranges approximately from how many weeks?

Accepted Answer

Introduction / Context: Oxidation ponds (also called waste stabilization ponds) are low-cost, land-intensive biological treatment units that rely on algae–bacteria symbiosis for BOD removal and pathogen die-off. Proper design requires choosing a detention time that balances treatment performance with land area and climatic conditions. Given Data / Assumptions: Facultative pond (not aerated lagoon or maturation pond). Typical temperate to warm climate conditions and standard organic loading. Question seeks a representative design range in weeks. Concept / Approach: Detention time in facultative ponds is influenced by temperature, solar radiation, and loading. Textbook values often fall in the multi-week range to achieve substantial BOD reduction and pathogen control. Common design practice cites about 3–6 weeks; many exam references round this to 4–5 weeks as a representative figure, assuming moderate loading and typical climates. Therefore, among the options, 4 to 5 weeks captures the mainstream design window for such ponds. Step-by-Step Solution: Identify the pond type: facultative oxidation pond.Recall common detention time guidance: several weeks rather than days.Select the option that best represents typical practice: 4 to 5 weeks. Verification / Alternative check: Design charts and case studies show BOD and coliform reductions improving significantly when detention exceeds roughly one month under favourable climates, aligning with 4–5 weeks. Why Other Options Are Wrong: 1 to 2 weeks: Short for many climates; more typical of aerated lagoons or high-rate units. 9 to 10 or 15 to 20 weeks: Possible in cold climates or very conservative designs, but not typical. 2 to 3 weeks: Borderline; often insufficient for consistent pathogen reduction in standard facultative ponds. Common Pitfalls: Confusing aerated lagoon detention (days) with facultative pond detention (weeks); not accounting for seasonal temperature effects on sizing. Final Answer: 4 to 5

Question 8

Sources of ozone generation in air
Which of the following is NOT a source that generates ozone in the surrounding atmosphere during normal operation?

Accepted Answer

Introduction / Context: Ozone (O3) can be intentionally produced (e.g., in sterilisation) or incidentally formed by electrical discharges and strong ultraviolet radiation acting on oxygen. Understanding everyday sources helps in indoor air quality assessments and occupational safety planning. Given Data / Assumptions: We are concerned with routine operation, not accidental fires or failures. Devices known for corona discharge or strong UV can create ozone locally. Household refrigerators are considered in normal working condition. Concept / Approach: Photocopiers and laser printers can generate ozone via corona discharge in their high-voltage sections. High-voltage electrical equipment (transformers, Tesla coils) also forms ozone around sparks/corona. Dermatological phototherapy equipment may emit UV wavelengths capable of producing ozone in room air if not fully contained or filtered. In contrast, refrigerators do not create ozone; historic concerns with them were about refrigerants (e.g., CFCs) depleting stratospheric ozone after release, not generating ozone locally in rooms. Step-by-Step Solution: List typical ozone-forming mechanisms: corona discharge and short-wave UV.Match these mechanisms to the devices provided.Identify the device without such mechanisms in normal use: refrigerators. Verification / Alternative check: Indoor air quality guidance notes commonly cite photocopiers and high-voltage devices as incidental ozone sources; refrigerators are not on such lists. Why Other Options Are Wrong: Xerox machines: Known incidental ozone producers; many contain ozone filters. Dermatological phototherapy: Produces strong UV; can generate ozone if unfiltered. High-voltage equipment: Corona discharge readily forms ozone. Ozone generators: Deliberately produce ozone for treatment; obviously a source. Common Pitfalls: Confusing “ozone depletion” (a stratospheric chemistry issue) with “ozone generation” (local indoor air emission), which are distinct phenomena. Final Answer: Refrigerators

Question 9

Consequences of global warming and climate change
Which outcomes are commonly associated with a warming climate on regional to global scales?

Accepted Answer

Introduction / Context: Global warming alters atmospheric and oceanic energy balances, influencing hydrology, storm dynamics, and agricultural systems. Environmental engineers and planners must anticipate multiple, interrelated impacts rather than a single isolated effect when considering adaptation and resilience projects. Given Data / Assumptions: Warming trend leads to changes in rainfall intensity and distribution. Warmer sea-surface temperatures can affect cyclone formation and intensity. Agricultural productivity responds to temperature, precipitation, and extreme events. Concept / Approach: Higher atmospheric moisture capacity (per Clausius–Clapeyron relation) supports more intense precipitation events, contributing to flooding. Ocean warming and changing wind shear conditions can influence the frequency and intensity of tropical cyclones in some basins. Heat stress, shifting seasons, water scarcity, and increased pest pressure can decrease food productivity in vulnerable regions. Therefore, floods, cyclonic impacts, and reduced crop yields are all credible and widely cited outcomes connected with climate warming, making the comprehensive choice correct. Step-by-Step Solution: Identify hydrologic impacts: heavier rainfall extremes increase flood risk.Consider storm dynamics: warmer seas can fuel stronger cyclones given conducive conditions.Assess agriculture: heat/water stress and extremes can lower yields. Verification / Alternative check: Assessment reports consistently project increased heavy precipitation events, coastal flood exposure, and climate-sensitive reductions in yields for key crops without adaptation, supporting the combined answer. Why Other Options Are Wrong: Each single impact (a, b, or c) is incomplete; climate change affects multiple systems simultaneously. None of these: Contradicts the established scientific understanding. Common Pitfalls: Assuming uniform global behaviour; regional variability exists, but the listed impacts are broadly consistent with observed and projected trends. Final Answer: All (a), (b) and (c)

Question 10

Gas cleaning for sulphur dioxide (SO2)
Which material is used as an adsorbent or chemisorbent to remove SO2 from gas/air streams in control equipment?

Accepted Answer

Introduction / Context: Sulphur dioxide control is central to flue-gas cleaning for boilers, furnaces, and process vents. Engineers can choose among dry, semi-dry, and wet scrubbing routes. Some media physically adsorb SO2, while others remove it by chemisorption or neutralisation, which in practice is often grouped under “adsorbent” in exam contexts when a solid bed is used. Given Data / Assumptions: Removal of SO2 from gas or air. Focus on common solid media used industrially or in teaching examples. Terminology allows chemisorption on solids to be considered within an adsorbent framework. Concept / Approach: Alkalised alumina (sodium-impregnated alumina) removes SO2 by chemisorption, forming sulphates/sulphites; it has been used in fixed-bed desulphurisation. Limestone powder (CaCO3) is widely used in dry and wet scrubbing where it neutralises SO2 to calcium sulphite/sulphate; while often described as an absorbent in slurries, dry injection processes effectively utilise the solid surface for reaction. Thus the option that includes alkalised alumina (a canonical SO2 chemisorbent) is the best match among the choices provided. Step-by-Step Solution: List common SO2 sorbents: alkalised alumina, lime/limestone, activated carbon (with catalysts), metal oxides.Match with options given; identify the one naming alkalised alumina explicitly.Select “Limestone powder or alkalised alumina.” Verification / Alternative check: Process control texts describe fixed-bed alkalised alumina systems and limestone-based FGD as standard methods for SO2 removal. Why Other Options Are Wrong: Bog iron: Used historically for H2S removal, not primary SO2 sorbent. Silica gel: A desiccant; poor affinity for SO2 removal applications. Active carbon: Can adsorb SO2 with impregnation, but the given option expressly names a classic chemisorbent. Zeolite 13X: Used for drying and hydrocarbon separation; not typical for SO2 control. Common Pitfalls: Confusing wet absorption chemistry with solid-bed chemisorption terminology; exams may treat both under a broad “adsorbent” label depending on context. Final Answer: Limestone powder or alkalised alumina

Question 11

Toxicity ranking in water pollution
Among the following, which is considered the most lethal class of water pollutants to aquatic life at low concentrations?

Accepted Answer

Introduction / Context: Different pollutants harm aquatic ecosystems through various mechanisms: toxicity, oxygen demand, pH alteration, turbidity, or eutrophication. Acute lethality at low concentrations is characteristic of certain organic and inorganic poisons that directly disrupt respiration or cellular metabolism in fish and invertebrates. Given Data / Assumptions: Comparison is about acute lethality at relatively low concentrations. Typical receiving waters without extraordinary buffering or dilution. Focus on broad pollutant categories listed in the options. Concept / Approach: Phenols and cyanides are notorious for high aquatic toxicity. Cyanide forms undissociated hydrogen cyanide (HCN), a fast-acting respiratory poison. Phenolic compounds disrupt membranes and can be lethal in the mg/L range. Chlorine is also toxic, but it dissipates/reacts and is typically dosed deliberately at low levels in water treatment; in receiving waters it is regulated to very low residuals. Alkalis primarily shift pH, and suspended solids exert physical rather than strong toxic chemical effects. Therefore, the most lethal class listed is phenol and cyanide. Step-by-Step Solution: Consider acute LC50 values: cyanide and phenols are in low mg/L to sub-mg/L ranges for sensitive species.Compare with chlorine, alkalis, and suspended solids which act through different, often more manageable mechanisms.Select “Phenol and cyanide.” Verification / Alternative check: Ecotoxicology references consistently rank cyanide among the most acutely toxic common industrial pollutants; many phenols also have low LC50 values for fish. Why Other Options Are Wrong: Chlorine: Toxic but typically controlled; its persistence is limited by reactions. Alkalis: Harm via pH changes; toxicity depends on buffering; not inherently as lethal at low concentrations. Suspended solids: Cause turbidity/smothering rather than strong acute toxicity at very low levels. Phosphates: Drive eutrophication, not acute lethality. Common Pitfalls: Equating regulatory stringency (e.g., very low chlorine residuals) with inherent lethality ranking; the mechanisms and contexts differ. Final Answer: Phenol and cyanide

Question 12

Controlling equipment noise
High noise levels produced during operation of fans and compressors can most directly be reduced by using which measure at the source or on the duct?

Accepted Answer

Introduction / Context: Mechanical equipment such as fans and compressors generate broadband noise from aerodynamic turbulence, blade-pass tones, and mechanical vibration. Environmental and occupational noise control aims to attenuate these emissions cost-effectively while maintaining system performance (airflow, pressure). Given Data / Assumptions: We are concerned with typical plant fans, blowers, and compressors. Noise is carried via air paths (intake/exhaust) and structure-borne paths. Question asks for a primary, direct reduction method. Concept / Approach: Mufflers (silencers) installed on intakes and discharges target the dominant airborne path and are specifically engineered for attenuation across target frequencies. They incorporate reactive and/or absorptive sections that interrupt sound transmission while allowing flow. Acoustical absorbents and lagging can reduce reverberant-field levels and transmission through ducts but are often supplementary; the most direct and effective first measure for air-borne fan/compressor noise is a properly designed silencer close to the source. Step-by-Step Solution: Identify main noise path: airborne in intake/discharge ducts.Choose treatment that directly attenuates this path without major performance loss.Select “Mufflers (silencers)” as the principal control measure. Verification / Alternative check: Noise control handbooks consistently recommend silencers as primary controls for duct-borne noise from fans and compressors, with lining and lagging as complements. Why Other Options Are Wrong: Acoustical absorbent: Helps in room treatment and duct lining, but not as directly effective alone as a tuned silencer. Lagging of noisy duct: Reduces breakout, but leaves the main intake/exhaust path less treated. None of these: Incorrect as silencers are standard practice. Raising fan speed: Increases noise; counterproductive. Common Pitfalls: Overreliance on room treatment while ignoring source-path controls; neglecting pressure drop considerations when selecting silencers. Final Answer: Mufflers (silencers)

Question 13

Sewage treatment – fine grit removal
Fine grit present in sewage is removed in which unit operation during preliminary treatment?

Accepted Answer

Introduction / Context: Preliminary treatment in wastewater plants protects downstream equipment by removing coarse and abrasive materials. Grit causes wear in pumps and reduces digester volume if not intercepted. Depending on particle size and specific gravity, different units are adopted to remove sand and fine mineral matter effectively. Given Data / Assumptions: “Fine grit” refers to smaller, more difficult-to-settle mineral particles than those captured in standard grit chambers. Conventional municipal plant; no special high-rate devices assumed. Aim is to identify the unit commonly specified for finer grit capture. Concept / Approach: Standard horizontal-flow or aerated grit chambers target typical grit sizes but may pass the finer fraction. A detritus tank (sometimes called a fine-grit chamber) is designed with controlled velocities and detention to enhance removal of finer mineral particles. Trickling filters and primary clarifiers serve biological and sedimentation roles for organics, not specific abrasive grit capture, and skimming tanks remove floatables like grease and oil rather than heavy grit. Step-by-Step Solution: Distinguish between coarse grit removal and finer grit interception.Associate the specialised unit for fine mineral solids with the term “detritus tank.”Select “Detritus tank.” Verification / Alternative check: Plant layouts in design texts show detritus tanks downstream of coarse screening and standard grit chambers when fine grit is a concern (e.g., sandy sewers). Why Other Options Are Wrong: Grit chamber: Removes coarser grit; less effective for fine fractions targeted by a detritus tank. Trickling filter: Biological treatment, not abrasive solids removal. Skimming tank: Removes floatables, not heavy grit. Primary clarifier: Settles organics; not optimised for fine gritty minerals. Common Pitfalls: Assuming a generic “grit chamber” removes all sizes; in practice, fine grit often requires a dedicated detritus tank or advanced grit removal technology. Final Answer: Detritus tank

Question 14

Industrial sources of arsenic pollution
Arsenic pollutants are typically NOT generated in which of the following industries under normal operations?

Accepted Answer

Introduction / Context: Arsenic is a toxic metalloid associated with a range of industrial activities. Correctly identifying sectors that can release arsenic helps in permitting, monitoring, and pollution control planning, while also clarifying which sectors generally do not pose arsenic emission risks under routine conditions. Given Data / Assumptions: Normal operations without accidental contamination. Typical process chemistries characteristic of the listed industries. Focus on arsenic generation or release as a pollutant, not occasional trace presence in raw materials. Concept / Approach: Tanneries may handle chemicals and hides containing trace metals; arsenic compounds have historically been used in some preservation processes. Glass and ceramic industries can incorporate metal oxides and mineral raw materials with arsenic impurities, potentially releasing arsenic in dusts or fumes. Non-ferrous smelting is a well-known source of arsenic emissions due to arsenic-bearing ores. In contrast, beverage production involves food-grade ingredients and hygienic processing; while trace arsenic in water sources is a quality concern, the industry does not generate arsenic pollutants as part of its process—it relies on clean inputs and treatment to meet strict standards. Step-by-Step Solution: Evaluate each industry for likely arsenic-bearing raw materials or high-temperature mineral processing.Recognise beverages production as non-mineral, non-smelting, and food-grade.Select “Beverages” as the industry not generating arsenic pollutants. Verification / Alternative check: Environmental inventories attribute arsenic emissions primarily to metal smelting, coal combustion, and certain mineral industries; food and beverage plants are not listed as sources beyond potential raw water contamination control. Why Other Options Are Wrong: Tanneries: Potential for arsenic in chemical streams historically; regulatory controls apply. Glass and ceramic: Mineral inputs may carry arsenic impurities; high-temperature processes can volatilise them. Any of these: Incorrect since beverages are not a generator. Non-ferrous metal smelting: A recognised arsenic source from arsenopyrite and similar ores. Common Pitfalls: Confusing contamination in incoming potable water with process generation; the question targets generation as a pollutant source. Final Answer: Beverages

Question 15

Air pollution toxicology and public health: Carbon monoxide (CO) in ambient air can originate from natural decomposition of chlorophyll and from haemoglobin breakdown in some animals, in addition to large anthropogenic sources such as incomplete com…

Accepted Answer

Introduction / Context: Carbon monoxide (CO) is a colorless, odorless gas produced by incomplete combustion of carbonaceous fuels and also by certain natural processes. Because CO binds strongly to haemoglobin in the blood, exposure above safe limits can rapidly impair oxygen transport. This question tests recognition of the dominant human health effect when concentrations exceed a typical threshold limit value (TLV) on the order of 50 ppm for workplace contexts or much lower for ambient guidelines. Given Data / Assumptions: CO concentration considered is beyond TLV (greater than about 50 ppm). Exposure is acute or short term, sufficient to cause clinical effects. Population is assumed to be unprotected and breathing ambient air. Concept / Approach: CO has a high affinity for haemoglobin, forming carboxyhaemoglobin (COHb). This competitively inhibits oxygen binding and shifts the oxygen–haemoglobin dissociation curve, reducing tissue oxygen delivery. The net physiological outcome is hypoxia, presenting as headache, dizziness, confusion, loss of coordination, and at higher levels, loss of consciousness and death by asphyxia. CO is not a meaningful greenhouse gas on policy timescales, nor does it directly alter sea level. Step-by-Step Solution: Identify the toxicological mechanism: COHb formation reduces blood oxygen-carrying capacity.Relate mechanism to symptomatology: hypoxia leads to asphyxial outcomes.Select the option that states the principal health effect: asphyxia. Verification / Alternative check: Clinical guidance links percent COHb to symptom severity; values above 10–20% produce neurological symptoms, and higher levels can be fatal. This aligns with the characterization of CO as an asphyxiant rather than as a greenhouse gas of concern. Why Other Options Are Wrong: Greenhouse/temperature increase and sea level rise: CO is not a major radiative forcing gas; these outcomes are associated with CO2 and other greenhouse gases.Enhances greenhouse effect: While CO can indirectly affect atmospheric chemistry, the immediate health concern at TLV exceedance is asphyxia. Common Pitfalls: Confusing CO with CO2 in climate discussions. Underestimating danger due to CO being odorless and colorless. Final Answer: causes asphyxia

Question 16

Environmental statements and climate impacts: Identify the correct statement regarding greenhouse effect, global warming, atmospheric chemistry, and air toxics.

Accepted Answer

Introduction / Context: Climate and air quality literacy requires distinguishing accurate statements from common misconceptions. Greenhouse forcing mechanisms, natural atmospheric chemistry, and health effects of pollutants are frequently mischaracterized. This item asks you to select the correct statement among four concise claims about deforestation, global warming, lightning chemistry, and sulphur dioxide health effects. Given Data / Assumptions: Greenhouse effect refers to warming due to heat-trapping gases (e.g., CO2, CH4, N2O). Extreme weather and agricultural productivity are sensitive to climate change. Lightning-driven chemistry predominantly involves nitrogen species. SO2 is a respiratory irritant rather than a simple asphyxiant. Concept / Approach: Evaluate each claim against well-established environmental science. Deforestation removes a carbon sink and typically worsens greenhouse gas accumulation. Global warming can reduce yields through heat stress, droughts, floods, and pest pressure, and it is associated with changing patterns and intensities of extreme events. Lightning discharges primarily produce nitrogen oxides (NO and NO2), not sulphur gases. Sulphur dioxide causes bronchoconstriction and airway irritation; its lethality is not via classic asphyxiation like carbon monoxide or nitrogen displacement. Step-by-Step Solution: Check option A: false; deforestation intensifies greenhouse forcing.Check option B: true; warming can diminish crop productivity and increase flood/cyclone risks through altered hydrology and storm dynamics.Check option C: false; lightning is a major natural source of NOx, not SO2 or H2S.Check option D: false; SO2 irritates and inflames airways; death is usually from respiratory failure, not asphyxia via haemoglobin binding. Verification / Alternative check: IPCC assessments and agronomic studies report yield declines for staples beyond certain temperature thresholds and increased risk of hydrometeorological extremes, corroborating option B. Why Other Options Are Wrong: A: Deforestation reduces carbon sequestration; it does not control greenhouse effect.C: Misstates lightning chemistry.D: Misclassifies toxicological mechanism of SO2. Common Pitfalls: Conflating any harmful gas with an asphyxiant. Assuming all natural electrical activity yields sulphur pollutants. Final Answer: Global warming is detrimental for food productivity and may lead to floods and cyclones.

Question 17

Photochemical and classical smog formation: Smog episodes are driven by precursors such as sulphur dioxide, nitrogen oxides, hydrocarbons, sunlight, and stagnant air. Which gas listed below does not directly contribute to smog formation mechanisms?

Accepted Answer

Introduction / Context: Smog is a mixture of pollutants and secondary products that impair visibility and harm health. Two main types are recognized: classical (sulphurous) smog and photochemical (oxidant) smog. While many gases coexist in urban air, only some are reactive precursors that drive smog chemistry. This question asks which listed gas is not a direct participant in smog formation. Given Data / Assumptions: Classical smog involves SO2 and particulates under humid conditions. Photochemical smog involves NOx and volatile organic compounds (VOCs) under sunlight. CO2 is abundant but relatively unreactive on urban smog timescales. Concept / Approach: Sulphur dioxide oxidizes to sulphates and contributes to haze and acidity; nitrogen oxides are central to ozone formation via photolysis and radical chemistry. Carbon dioxide is a stable greenhouse gas that does not partake in the rapid chain reactions forming ozone, peroxyacyl nitrates, or secondary aerosols during smog events. Therefore, CO2 is not a smog precursor even though it is co-emitted from combustion sources. Step-by-Step Solution: List known smog precursors: SO2, NOx, VOCs, ammonia, and particulates.Assess each option's role: SO2 and NOx participate directly; CO2 does not.Select CO2 as the gas not forming smog. Verification / Alternative check: Urban photochemical modeling frameworks (e.g., ozone isopleths) exclude CO2 from precursor control strategies, confirming its non-participation in smog chemistry. Why Other Options Are Wrong: SO2: Oxidizes to sulphate aerosol; key in classical smog and acid rain chemistry.NOx: Essential for ozone production and oxidant cycles.Any of these: Incorrect because not all listed gases drive smog; CO2 is the exception. Common Pitfalls: Equating greenhouse gases with air quality drivers. Assuming any combustion product contributes to smog chemistry. Final Answer: CO2

Question 18

Wastewater discharge standards: The threshold limit value (TLV) for lead (Pb) in public sewer or wastewater is closest to which value (in ppm) under typical regulatory guidelines?

Accepted Answer

Introduction / Context: Lead is a toxic heavy metal that accumulates in biological systems and poses severe health risks. Wastewater discharge standards therefore specify very low permissible concentrations to protect sewer infrastructure, treatment plant biology, and receiving waters. This question asks you to identify a representative threshold value in parts per million (ppm) for lead in public sewers. Given Data / Assumptions: We consider typical conservative regulatory guidance for public sewer discharges. Value is expected to be low due to toxicity and bioaccumulation. Answers are order-of-magnitude separated, testing recognition rather than memorization of a specific code. Concept / Approach: Lead's allowable limits for sewer discharge are often of the order of 1 ppm or less, reflecting the need to protect activated sludge microorganisms and avoid accumulation in biosolids. Much larger values such as 25–650 ppm would be incompatible with treatment plant operation and environmental protection goals. Step-by-Step Solution: Recall that heavy metals are stringently limited (sub-ppm to single-digit ppm).Compare options: 1 ppm is plausible; 25–650 ppm are orders of magnitude too high.Select 1 ppm. Verification / Alternative check: Municipal pretreatment programs frequently apply categorical limits around 0.5–2 mg/L (ppm) for lead, depending on jurisdiction and receiving treatment capability, supporting the 1 ppm choice as a representative figure. Why Other Options Are Wrong: 25, 150, 650 ppm: Far exceed typical pretreatment and environmental discharge limits; would threaten plant performance and water quality. Common Pitfalls: Confusing workplace air TLVs with water discharge limits. Assuming metals limits are similar to nutrient limits; metals are generally much lower. Final Answer: 1

Question 19

Structure of the atmosphere: What is commonly referred to as the “upper layer” of the Earth’s atmosphere in environmental engineering contexts concerned with radio communication and auroral phenomena?

Accepted Answer

Introduction / Context: The atmosphere is stratified into layers with distinct thermal and compositional characteristics: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. In many applied contexts, especially radio propagation and space weather, the term “ionosphere” is used to denote the upper ionized region that influences electromagnetic wave transmission and auroral activity. This question probes that terminology. Given Data / Assumptions: “Upper layer” is taken in a practical sense used in communications and environmental monitoring. Ionosphere spans portions of the mesosphere and thermosphere where ionization is significant. Troposphere and stratosphere are lower layers associated with weather and ozone, respectively. Concept / Approach: The ionosphere is not a distinct thermal layer but an electrified region extending roughly from about 60 km upward, with D, E, and F regions that reflect or refract radio waves. Environmental engineers may reference it in studies of solar storms, satellite links, and high-altitude phenomena, justifying its description as an upper atmospheric domain. Step-by-Step Solution: List major layers and their key features.Identify which one is associated with ionization and radio propagation: ionosphere.Select ionosphere as the commonly referenced “upper layer.” Verification / Alternative check: Textbooks often overlay the ionosphere across mesosphere/thermosphere in diagrams, labeling it as the operative upper layer for communications. Why Other Options Are Wrong: Stratosphere: Mid-atmosphere with ozone layer; not generally called the “upper layer.”Troposphere: Lowest layer where weather occurs.None: Incorrect because ionosphere fits the description. Common Pitfalls: Confusing thermal layers (stratosphere) with functional regions (ionosphere). Assuming “upper” always means exosphere; context matters. Final Answer: ionosphere

Question 20

Drinking water health effects: Excess nitrate (NO3-) in water above about 50 ppm is associated with which human health condition, especially in infants?

Accepted Answer

Introduction / Context: Nitrogen species in drinking water are tightly regulated. Elevated nitrate levels are a particular concern in agricultural regions due to fertilizer leaching. Infants are vulnerable to nitrate's conversion to nitrite in the gut, which can oxidize haemoglobin to methemoglobin, reducing oxygen transport. This item asks you to identify the classic health outcome linked to nitrate above approximately 50 ppm as NO3-. Given Data / Assumptions: Nitrate concentration in water exceeds about 50 ppm as NO3-. Population of concern includes infants under six months. Standard physiological mechanism of nitrate–nitrite–methemoglobin formation applies. Concept / Approach: In the infant gastrointestinal tract, certain bacteria reduce nitrate to nitrite. Nitrite oxidizes Fe2+ in haemoglobin to Fe3+, forming methemoglobin, which cannot carry oxygen. The resulting hypoxia manifests as cyanosis (blue baby syndrome). This pathway underlies regulatory limits and treatment goals for potable water supplies in agricultural catchments. Step-by-Step Solution: Identify the contaminant and its typical health endpoint: nitrate → methemoglobinemia.Recall the susceptible group: infants have higher gut conversion and lower methemoglobin reductase activity.Choose the option explicitly naming methemoglobinemia. Verification / Alternative check: Public health advisories and WHO/EPA guidance reference nitrate limits to prevent methemoglobinemia in infants, confirming the association. Why Other Options Are Wrong: Gastroenteritis: May co-occur from pathogens but is not the hallmark effect of nitrate.Asphyxiation: Implies airway obstruction or CO intoxication, not the nitrate mechanism.Tooth decay: Unrelated to nitrate exposure. Common Pitfalls: Confusing nitrate with nitrite; nitrite is the proximate oxidant, but nitrate is the regulated precursor. Assuming adults have the same susceptibility as infants; risk is lower in adults. Final Answer: methemoglobinemia (blue baby syndrome)

Environmental Engineering Questions