Question 1

Sanitation engineering — a below-ground masonry structure in which wastewater undergoes anaerobic decomposition by bacteria is called what?

Accepted Answer

Introduction: On-site sanitation systems often rely on primary treatment under anaerobic conditions. The question describes a masonry structure built below ground where wastewater is held for anaerobic bacterial action. Given Data / Assumptions: Structure: below ground, masonry construction. Process: anaerobic digestion of settled solids and scum. Application: on-site domestic wastewater treatment. Concept / Approach: A septic tank is a watertight underground chamber that provides quiescent conditions for sedimentation and scum accumulation, with anaerobic bacteria decomposing organic matter. Effluent typically flows to a soak pit or drain field. Step-by-Step Solution: 1) Match the process description (anaerobic bacterial action) to common units.2) Septic tanks are specifically designed for this purpose and are usually masonry or concrete underground units.3) Hence, “septic tank” best fits the given description. Verification / Alternative check: Standard sanitation texts define septic tanks in precisely these terms: underground, quiescent, anaerobic digestion with sludge retention. Why Other Options Are Wrong: Cesspool: essentially a soak pit or leach pit without proper treatment staging. Lagoon: large, mostly aerobic or facultative surface ponds, not small masonry chambers. Skimming mill: not a wastewater treatment unit. Common Pitfalls: Confusing cesspools with septic tanks; cesspools lack the defined retention and treatment stages of septic systems. Final Answer: The described unit is a septic tank.

Question 2

Thermal pollution — in aquatic systems, an increase in water temperature chiefly reduces which critical water-quality parameter, leading to stress on aquatic life?

Accepted Answer

Introduction: When warm effluents enter rivers or lakes, the physical chemistry of water changes. The key ecological concern is the effect on oxygen availability to aquatic organisms. The question asks which parameter is reduced primarily by temperature rise. Given Data / Assumptions: Parameter candidates: dissolved oxygen (DO), biological oxygen demand (BOD), vapor pressure. Effect considered: consequence of increased water temperature. Aquatic ecology: fish and invertebrates require adequate DO. Concept / Approach: Solubility of gases in water decreases as temperature increases. Thus DO saturation concentration falls with higher temperature, reducing available oxygen even if pollution loads are unchanged. Step-by-Step Solution: 1) Evaluate DO: temperature rise lowers oxygen solubility, so DO tends to decrease.2) Evaluate BOD: this is a demand metric; it often increases in effect due to faster reaction rates, not decreases.3) Evaluate vapor pressure: water vapor pressure increases with temperature, not decreases.4) Therefore, the parameter reduced by heating is dissolved oxygen content. Verification / Alternative check: DO saturation tables show a monotonic decrease of DO with increasing temperature, confirming the conclusion. Why Other Options Are Wrong: BOD: represents oxygen demand; temperature often accelerates biochemical activity, effectively increasing oxygen consumption rather than reducing BOD numerically by heating alone. Vapor pressure: rises with temperature. All of the above: invalid since items (b) and (c) are not reduced. Common Pitfalls: Confusing BOD increase in reaction rate with a decrease in its numerical value; the central physical effect is reduced oxygen solubility. Final Answer: Water temperature rise primarily reduces dissolved oxygen content.

Question 3

Boiler feedwater — high-pressure units use deaeration chiefly to reduce which dissolved constituent and thereby limit corrosion?

Accepted Answer

Introduction: Corrosion in boilers is strongly accelerated by dissolved oxygen. Mechanical and thermal deaeration, often followed by chemical scavengers, is standard practice in high-pressure systems. The question asks what deaeration primarily reduces. Given Data / Assumptions: System: high-pressure boiler feedwater. Process: deaeration (mechanical/thermal). Goal: corrosion control via removal of dissolved gases. Concept / Approach: By heating and contacting water with steam in a deaerator, oxygen solubility drops and oxygen is stripped out. Remaining traces are scavenged (e.g., hydrazine or sulfite in some systems). Step-by-Step Solution: 1) Identify primary corrosion driver among options: dissolved oxygen.2) Recognize deaeration purpose: remove oxygen and other non-condensable gases.3) Select “its dissolved oxygen content” as the correct effect. Verification / Alternative check: Boiler water treatment guidelines prioritize oxygen removal to protect economizers and feed lines from pitting. Why Other Options Are Wrong: Foaming: controlled by antifoams, proper alkalinity, and solids management, not by deaeration alone. Silica: addressed via demineralization; deaeration does not remove silica. Caustic embrittlement: managed through alkalinity control and metallurgy; not solved directly by deaeration. Common Pitfalls: Assuming deaeration is a substitute for full water treatment; it targets gases, not dissolved salts. Final Answer: Deaeration reduces the dissolved oxygen content of boiler feedwater.

Question 4

Industrial pollution — the common toxic pollutant associated with the chlor-alkali industry and also with certain battery manufacturing operations is which of the following?

Accepted Answer

Introduction: Process industries may release characteristic pollutants depending on technology. Historically, the chlor-alkali industry used mercury cell technology, and mercury compounds have also been used in certain battery types. The question asks for the common pollutant linked to both sectors. Given Data / Assumptions: Industry 1: chlor-alkali (chlorine and caustic soda production). Industry 2: battery manufacture (not limited to modern lithium-ion chemistry). We are focusing on historically significant pollutants. Concept / Approach: Mercury cell electrolyzers (now phased out in many places) used liquid mercury as a cathode, causing mercury emissions when controls were inadequate. Mercury batteries (e.g., mercuric oxide) were once common for small devices. Step-by-Step Solution: 1) Identify hallmark pollutant from mercury-cell chlor-alkali: mercury.2) Cross-check with battery manufacture history: mercury compounds used in button cells and other designs.3) Select “mercury” as the pollutant common to both. Verification / Alternative check: Regulatory transitions away from mercury cells and restrictions on mercury in batteries reinforce this association. Why Other Options Are Wrong: Brine: a process feed, not a pollutant per se. Phosphate: associated with detergents or fertilizers, not these specific industries. None of these: incorrect because mercury is well-documented. Common Pitfalls: Assuming contemporary membrane cell plants imply no historical pollutant; the question references the known legacy issue. Final Answer: Mercury is the characteristic pollutant associated with both sectors.

Question 5

Which common air pollutant does not typically cause vegetation damage (i.e., is not phytotoxic at ambient urban concentrations)?

Accepted Answer

Introduction / Context: Many gaseous air pollutants injure crops and trees by disrupting photosynthesis, damaging leaf tissues, or altering plant metabolism. However, not every common pollutant is strongly phytotoxic at concentrations typically found in ambient air around cities and highways. Given Data / Assumptions: The question asks for the pollutant that does not harm vegetation under usual ambient exposures. Consider well-known phytotoxic agents (ozone, SO2, HF, NOx) versus relatively non-phytotoxic gases like CO. Context is general urban/industrial air, not acute spill conditions. Concept / Approach: Phytotoxicity depends on reactivity and plant uptake. Ozone is a powerful oxidant causing stippling and necrosis. SO2 forms acidic species in leaf tissues. Fluorides are notorious for leaf-tip burn at very low concentrations. Some herbicides (weed killers) drifting off-target cause direct injury. By contrast, carbon monoxide (CO) is relatively unreactive in plant biochemical pathways and at ambient levels is not a typical cause of vegetation damage. Step-by-Step Solution: 1) List common phytotoxic pollutants: O3, SO2, HF, certain NOx and herbicide vapors.2) Identify their plant injury signatures (chlorosis, necrosis, reduced growth).3) Evaluate CO: limited plant uptake/impact at ambient levels; not a typical phytotoxic agent.4) Therefore, select CO as the non-damaging option. Verification / Alternative check: Standard environmental texts consistently implicate ozone, SO2, HF, and some NOx as phytotoxic; CO rarely appears on lists of vegetation-damaging pollutants at ambient concentrations. Why Other Options Are Wrong: Smog/ozone: ozone is strongly phytotoxic (leaf stippling, yield loss).HF/NOx: HF is highly injurious; NOx can contribute to ozone/acid deposition.SO2/weed-killer drift: both are known to injure plants.Ammonia: at sufficient levels causes leaf burn and imbalance. Common Pitfalls: Assuming all air pollutants harm plants equally; ignoring that CO’s major risk is to humans (carboxyhemoglobin), not to vegetation at ambient levels. Final Answer: Carbon monoxide

Question 6

In boiler-feed-water conditioning, which unit process is used specifically to remove dissolved (soluble) silica from the water?

Accepted Answer

Introduction / Context: Silica control is a critical objective in boiler-feed-water treatment because silica volatilizes and deposits on turbine blades and heat-transfer surfaces, reducing efficiency and causing maintenance issues. Unlike suspended solids, dissolved silica requires a selective removal step. Given Data / Assumptions: Target constituent: dissolved (reactive) silica, not particulate silica only. Boiler duty may require very low silica (ppb levels) for high-pressure systems. Common pretreatment steps (coagulation, filtration) chiefly remove turbidity and colloids. Concept / Approach: Dissolved silica (as monomeric silicic acid species) is effectively removed by strong-base anion (SBA) exchange resins, often in conjunction with demineralization trains (cation exchanger → degasser → anion exchanger → mixed bed). Coagulation/filtration are insufficient for dissolved silica; thermal conditioning may shift equilibria but does not reliably meet low-silica specifications. Step-by-Step Solution: 1) Distinguish between particulate vs dissolved silica.2) Map removal technologies: particulate silica → clarification/filtration; dissolved → SBA resin.3) Select strong-base anion exchange for specific dissolved silica removal.4) Note that polishing by mixed-bed may follow to achieve ppb levels. Verification / Alternative check: Boiler water handbooks specify SBA or weak-base + strong-base sequences for silica control, with mixed-bed polishing where required. Why Other Options Are Wrong: Coagulation: targets colloids/suspended solids, not dissolved silica to low ppb.Pressure filtration: removes particles, not dissolved species.Preheating: may reduce carbon dioxide or assist deaeration; does not reliably remove dissolved silica.Aeration: oxidizes/strips gases; not for silica. Common Pitfalls: Confusing particulate turbidity control with dissolved silica removal; overlooking need for resin regeneration and silica leakage monitoring. Final Answer: Strong-base anion exchange

Question 7

Exposure to sulphur dioxide (SO2) in chimney/flue gases commonly leads to material and process impacts including fabric deterioration, accelerated metal corrosion, and adverse effects on paint drying—identify the correct overall assessment.

Accepted Answer

Introduction / Context: Sulphur dioxide is a major combustion by-product when sulfur-bearing fuels are burned. In the atmosphere or within industrial environments, SO2 and its oxidation products can damage materials and interfere with surface-coating processes. Given Data / Assumptions: SO2 may oxidize to sulfuric acid aerosols in moist air. Materials exposed include metals, fabrics (leather/cloth), and painted surfaces. Question asks whether these effects co-occur. Concept / Approach: SO2 promotes corrosive environments (acidic condensation) that increase metal corrosion rates. Fabrics and leather are susceptible to chemical attack and discoloration under SO2/acidic mists. Paint films can experience curing interference or surface defects due to acid gases and particulate sulfates, altering drying/hardening characteristics. Step-by-Step Solution: 1) Identify mechanisms: SO2 + H2O + O2 → acidic species (e.g., H2SO4).2) Metals: low pH films accelerate corrosion.3) Fabrics/leather: chemical degradation/discoloration in polluted air.4) Paints: acid gases can inhibit oxidation/polymerization or cause surface defects, affecting drying time. Verification / Alternative check: Industrial hygiene and corrosion references report multi-material susceptibility in SO2-rich atmospheres; urban pollution control often targets SO2 specifically for such reasons. Why Other Options Are Wrong: A, B, C individually: each is true but incomplete; the comprehensive correct assessment is that all occur.None: contradicted by established field and lab observations. Common Pitfalls: Attributing all damage solely to particulate matter; ignoring humidity’s role in acid formation. Final Answer: All of the above effects occur

Question 8

On the Ringelmann smoke chart, what approximate percentage blackness corresponds to “Chart No. 2”?

Accepted Answer

Introduction / Context: The Ringelmann chart is a visual tool used to estimate smoke opacity from stacks by comparing plume darkness against standardized grayscale patterns. Each numbered chart level correlates with an approximate “percent black” or opacity. Given Data / Assumptions: We need the opacity that corresponds to Chart No. 2. Standard mapping: 0 (0%), 1 (~20%), 2 (~40%), 3 (~60%), 4 (~80%), 5 (~100%). Concept / Approach: Memorize or reference the canonical mapping between Ringelmann numbers and percent blackness. Chart No. 2 is commonly taken as approximately 40 percent black/opacity. Step-by-Step Solution: 1) Recall the sequence: 0, 20, 40, 60, 80, 100 percent for Ringelmann 0–5.2) Locate No. 2 → 40 percent.3) Choose the matching option. Verification / Alternative check: Environmental compliance guides and stack-observer manuals use this mapping for quick field estimates. Why Other Options Are Wrong: 10%/20%: correspond to lighter plumes (No. 0–1).80%/100%: correspond to Ringelmann 4–5, much darker than No. 2. Common Pitfalls: Confusing percent blackness with percent light transmittance; environmental rules sometimes specify maximum Ringelmann numbers—knowing mappings avoids violations. Final Answer: 40 percent black

Question 9

Inhalation of respirable crystalline silica dust (e.g., during drilling/mining/refractory work) primarily causes silicosis—a fibrotic lung disease—characterized early by progressive shortness of breath; identify the typical outcome/symptom.

Accepted Answer

Introduction / Context: Chronic inhalation of respirable crystalline silica (quartz, cristobalite, tridymite) is a classic occupational hazard in mining, stone cutting, foundries, and refractory manufacture. The hallmark disease is silicosis, a pneumoconiosis involving lung fibrosis that progressively impairs gas exchange. Given Data / Assumptions: Exposure occurs in settings like mica/lead/zinc mining, foundries, refractories. Question seeks a typical health effect attributable to silica dust inhalation. We require exactly one correct option; Recovery-First clarifies symptom-level outcome. Concept / Approach: Pathophysiology: silica particles deposit in alveoli, activate macrophages, and induce fibrotic nodules. Clinically, this manifests as exertional dyspnea that may progress to breathlessness at rest, with cough and reduced lung function. Silica exposure also increases susceptibility to tuberculosis, but TB is not an inevitable or immediate direct outcome for every exposed worker; dyspnea due to silicosis is the characteristic, consistent effect. Step-by-Step Solution: 1) Map exposure → disease: silica → silicosis (fibrotic lung disease).2) Identify cardinal symptom: progressive shortness of breath from reduced pulmonary compliance and gas exchange.3) Exclude distractors unrelated to silica (metal fume fever, otitis media, cyanide toxicity).4) Exclude immediate suffocation (asphyxiation) which is not the mechanism of silica toxicity. Verification / Alternative check: Occupational medicine references consistently list dyspnea and restrictive defects on spirometry as primary clinical features; radiographs show small rounded opacities predominantly in upper lobes. Why Other Options Are Wrong: Asphyxiation: acute oxygen displacement hazard, not typical of silica.Metal fume fever: linked to zinc oxide fumes in welding/galvanizing.Otitis media: ENT condition unrelated to dust pneumoconiosis.Cyanide poisoning: toxicological scenario unrelated to silica dust. Common Pitfalls: Assuming silica directly “causes tuberculosis” in all cases; it increases susceptibility but TB is not universal. Final Answer: Progressive shortness of breath (dyspnea)

Question 10

In furnace operation, an increase in fuel firing rate by about 50% typically raises the noise level by approximately how many decibels (dB)?

Accepted Answer

Introduction / Context: Industrial furnace noise arises from combustion turbulence, air inspirators, burner dynamics, structure-borne vibrations, and process heat-load fluctuations. Sound levels are measured in decibels on a logarithmic scale, so changes in source power do not translate linearly to dB changes. Given Data / Assumptions: Fuel firing rate is increased by approximately 50% (i.e., power ratio ~1.5). Other conditions remain similar (geometry, acoustics, flow regime). We seek a typical order-of-magnitude change. Concept / Approach: dB level change due to a power ratio R is ΔL = 10 * log10(R). For R = 2 (doubling), ΔL ≈ 3 dB. For R = 1.5, ΔL ≈ 10 * log10(1.5) ≈ 1.76 dB. In practice, operational variability and multiple noise contributors often lead engineers to quote ~3 dB as the characteristic increase for substantial firing rate hikes, recognizing measurement uncertainty and concurrent airflow increases. Step-by-Step Solution: 1) Model the firing-rate change as a power increase.2) Compute ΔL = 10 * log10(1.5) ≈ 1.76 dB.3) Apply engineering rule of thumb: ~3 dB per near-doubling; real plants often observe ~2–3 dB for ~50%–100% increases.4) Select ~3 dB as the best discrete option provided. Verification / Alternative check: Acoustics texts and plant experience align on 3 dB ≈ doubling of acoustic power; measured changes around 2 dB are commonly rounded to the nearest practical value. Why Other Options Are Wrong: 30/70/100 dB: imply enormous power changes (orders of magnitude), unrealistic for a 50% firing increase.0 dB: contradicts the expected increase from higher combustion intensity and airflow. Common Pitfalls: Treating dB as linear; ignoring that multiple sound sources add logarithmically, not arithmetically. Final Answer: About 3 dB

Question 11

For removing very fine suspended solids and colloids from polluted water, which treatment step is most effective as the primary mechanism?

Accepted Answer

Introduction / Context: Colloids are particles that remain stably dispersed due to surface charge and Brownian motion, resisting gravity-driven settling. Effective removal requires destabilizing the colloids so that larger flocs form and can be separated by clarification or filtration. Given Data / Assumptions: Target: finely divided suspended solids and colloidal matter. Conventional treatment train: coagulation → flocculation → clarification/filtration. Mechanical mixing alone does not neutralize charge. Concept / Approach: Chemical coagulation (e.g., alum, ferric salts, PAC) neutralizes colloidal charges and promotes microfloc formation. Gentle mechanical flocculation then grows settleable flocs. Sedimentation without coagulation is ineffective for true colloids; clarifiers require prior destabilization to perform efficiently. Step-by-Step Solution: 1) Diagnose the removal barrier: electrostatic stability of colloids.2) Apply coagulant to neutralize charges and sweep out fines.3) Provide flocculation to build larger aggregates.4) Remove flocs via clarification/filtration. Verification / Alternative check: Jar tests demonstrate dramatic turbidity reduction only when coagulants are dosed at appropriate pH/alkalinity; mechanical stirring without coagulant provides negligible removal. Why Other Options Are Wrong: Plain sedimentation/clarifier alone: poor for colloids that do not settle.Mechanical flocculation only: mixing without charge neutralization is ineffective.Screening: targets large debris, not colloids. Common Pitfalls: Underdosing/overdosing coagulant; ignoring pH/alkalinity; insufficient flocculation time or gradients. Final Answer: Chemical coagulation (with subsequent flocculation/clarification)

Question 12

In stack observations, a persistent “white smoke” or white plume from a furnace chimney generally indicates which combustion condition?

Accepted Answer

Introduction / Context: Stack plume appearance provides quick diagnostic clues about combustion quality. White plumes are common and often misunderstood compared to black or blue smoke. Understanding excess air and condensation phenomena helps operators tune burners appropriately. Given Data / Assumptions: Observation: persistent white plume visible from the chimney. Ambient conditions allow water-vapour condensation in the exhaust plume. Fuel/air ratio can be varied (excess air high or low). Concept / Approach: A high excess-air setting introduces surplus cool air, reducing flue-gas temperature. When the humid exhaust mixes with ambient air, water vapour condenses into fine droplets visible as a white plume. This is distinct from black smoke (soot from insufficient air) and blue smoke (unburned oil aerosols). White plumes can appear for gaseous or liquid fuels if conditions favour condensation; thus the diagnostic points to excess-air/temperature rather than fuel type per se. Step-by-Step Solution: 1) Note plume colour and persistence: stable white indicates condensed moisture.2) Link to thermodynamics: cooler flue gas from very high excess air increases relative humidity and condensation.3) Eliminate fuel-type-only explanations; both fuels can produce white condensation plumes.4) Select “very high excess air” as the most informative condition. Verification / Alternative check: Flue-gas analysers show higher O2 and lower CO with high excess air; stack temperature drops, and visible white plumes are common in cool, humid weather. Why Other Options Are Wrong: Very low excess air: tends to produce soot → darker smoke.Fuel-only choices: plume colour is not determined solely by fuel type.No condensables: contradicts visible white plume (water droplets are condensables). Common Pitfalls: Equating white plume with “clean combustion”; although not soot, it may signal efficiency loss due to over-ventilation. Final Answer: Very high excess air (cool plume with water-vapour condensation)

Question 13

Occupational exposure to excessive noise in the workplace can lead to multiple adverse outcomes; which overall assessment best reflects the health effects?

Accepted Answer

Introduction / Context: Chronic exposure to high sound levels damages the auditory system and has broader physiological and psychological consequences. Workplace standards specify permissible exposure limits and recommend hearing conservation programs to mitigate risks. Given Data / Assumptions: Noise levels can be continuous, intermittent, or impulsive. Exposure may be unprotected (no hearing protection). Question asks for a comprehensive assessment of impacts. Concept / Approach: Noise-induced hearing loss (NIHL) arises from damage to hair cells in the cochlea, typically affecting high frequencies first. Extreme impulsive noise can rupture the tympanic membrane. Non-auditory effects (stress response, sleep disturbance, reduced concentration) manifest as nervousness and fatigue, impairing safety and productivity. Step-by-Step Solution: 1) Associate chronic high dB exposure with NIHL—progressive, often irreversible.2) Recognize that very high peak levels (e.g., blasts) may rupture the eardrum.3) Include systemic effects: stress hormones, fatigue, irritability.4) Choose the option capturing all effects together. Verification / Alternative check: Occupational health literature documents both auditory and non-auditory outcomes; regulations require monitoring, engineering controls, and PPE. Why Other Options Are Wrong: Single-effect options ignore the multi-dimensional impact of noise.“None” contradicts extensive evidence. Common Pitfalls: Relying solely on earplugs without engineering controls; neglecting impulsive noise hazards. Final Answer: All of the above (hearing loss, possible eardrum rupture, nervousness/fatigue)

Question 14

Greenhouse gases trap outgoing terrestrial (infrared) radiation, warming the lower atmosphere. Which of the following gases does not exhibit a significant greenhouse effect under Earth tropospheric conditions?

Accepted Answer

Introduction / Context: Greenhouse gases (GHGs) absorb and re-emit infrared radiation, reducing the efficiency with which Earth loses heat to space. The major naturally occurring GHGs include water vapour, carbon dioxide, methane, nitrous oxide, and ozone; human activities have increased several of these concentrations. Given Data / Assumptions: We evaluate gases for significant IR absorption features in the thermal infrared window. Background gases like N2 and O2 are largely IR-inactive (no strong dipole moment changes in fundamental vibrational modes). We seek the non-GHG among common atmospheric gases. Concept / Approach: Molecules absorb IR when their vibrations change the dipole moment. Linear homonuclear diatomics such as N2 and O2 lack a permanent dipole and have vibrational modes that are IR-inactive, making them negligible greenhouse contributors despite their abundance. Conversely, CO2 (asymmetric stretch/bend), CH4 (multiple vibrational modes), N2O, and O3 have strong IR absorption bands and contribute to the greenhouse effect. Step-by-Step Solution: 1) List candidate gases and recall their IR activity.2) Identify N2 as a homonuclear diatomic with IR-inactive fundamental vibrations.3) Recognize CO2/CH4/N2O/O3 as established GHGs.4) Select N2 as the non-greenhouse gas in this set. Verification / Alternative check: Atmospheric spectroscopy data and climate texts consistently classify N2 (and O2) as non-GHG for IR absorption; any greenhouse influence is indirect (e.g., pressure broadening), not primary absorption. Why Other Options Are Wrong: CO2: strong 15 μm band and others; key anthropogenic GHG.CH4: potent GHG with absorption near 7.6 μm and others.N2O: long-lived GHG with strong IR bands.O3: absorbs in IR and UV; contributes to greenhouse effect. Common Pitfalls: Assuming abundance alone (N2) implies greenhouse effect; confusing UV absorption (O3) with lack of IR activity—ozone does both. Final Answer: Nitrogen (N2)

Question 15

Air pollution control context: Among common industrial sources, which plant does not typically emit an appreciable amount of sulphur dioxide (SO2) to the atmosphere under normal operation?

Accepted Answer

Introduction: Industrial sources release different primary air pollutants depending on feed, process chemistry, and control equipment. Sulphur dioxide, abbreviated as SO2, is a classic pollutant from the oxidation of sulphur present in fuels and certain ores. The question asks which listed plant does not normally emit appreciable SO2, which requires recalling the dominant chemistry and fuels used by each industry. Given Data / Assumptions: We consider routine, well operated plants. Fuel sulphur content and process gas composition define SO2 tendency. The options reflect typical large point sources. Concept / Approach: SO2 forms when sulphur oxidizes during combustion or is released from sulphide ores. Thermal power plants and petroleum refineries burn sulphur bearing fuels, so SO2 appears in flue gas unless desulphurised. Sulphuric acid manufacture begins with sulphur or sulphide oxidation to SO2 as an intermediate, so unmanaged streams may contain SO2. In contrast, nitric acid production centers on oxidizing ammonia to NO and NO2, yielding oxides of nitrogen rather than sulphur compounds, so appreciable SO2 is not characteristic of that stack. Step-by-Step Solution: Identify SO2 prone sectors: high sulphur fuels or sulphur feedstocks.Thermal power: coal and heavy oils contain sulphur, generating SO2.Refineries: process heaters and FCC regenerators burn sulphur bearing fuel gas and coke, forming SO2.Sulphuric acid plant: SO2 is a process intermediate to H2SO4, so leaks or tail gas can contain SO2.Nitric acid plant: core pollutant is NOx, not SO2, so SO2 emissions are not appreciable. Verification / Alternative check: Pollution control focus confirms this pattern: FGD targets SO2 at power plants; refineries implement sulphur recovery units; sulphuric plants use tail gas cleanup; nitric acid units install NOx abatement such as selective catalytic reduction, which addresses NO and NO2, not SO2. Why Other Options Are Wrong: Thermal power plant: burns sulphur containing fuel and forms SO2. Petroleum refinery: combustion and catalyst regeneration emit SO2. Sulphuric acid plant: SO2 is inherent to the process. Cement kiln: may emit SO2 from raw materials and fuel sulphur, though variable. Common Pitfalls: Assuming all large stacks behave similarly. Emissions mirror process chemistry. A plant focused on nitrogen oxidation will not inherently emit sulphur oxides. Final Answer: Nitric acid plant

Question 16

Particulate control selection: Which equipment is most efficient for removing submicronic dust particles from blast furnace gas?

Accepted Answer

Introduction: Blast furnace gas contains a wide size range of particulates. Efficient removal of submicronic particles requires an equipment principle that does not rely only on inertia or gravity. Selecting the best device hinges on the capture mechanism, pressure drop, and effectiveness at very small aerodynamic diameters. Given Data / Assumptions: Target: submicronic dust, typically less than 1 micron. Gas stream: blast furnace gas with high flow and variable composition. Industry objective: high collection efficiency with acceptable pressure drop. Concept / Approach: Gravity settling removes only very large particles. Cyclones and multiclones leverage inertia and centrifugal forces and lose efficiency as particle size approaches submicron. Wet scrubbers enhance impaction and diffusion but may struggle with the finest aerosols without high energy input. Electrostatic precipitators charge particles and drive them to collecting plates by electrostatic forces, enabling high efficiencies even for fine and submicronic fractions when designed correctly. Step-by-Step Solution: Screen out devices dominated by inertia or gravity for submicron particles.Recognize that ESPs apply electrical forces largely independent of particle inertia.Note that ESPs used on blast furnace gas are standard practice due to low pressure drop and high efficiency.Conclude that the electrostatic precipitator provides the most efficient submicron control among the listed options. Verification / Alternative check: Performance curves show ESP collection efficiency remains high for particles well below 1 micron, whereas cyclones drop off. High energy venturi scrubbers can collect fine particles but at a markedly higher pressure drop than ESPs. Why Other Options Are Wrong: Hydrocyclone and gravity settling: poor for very fine particles. Packed scrubber: better for soluble gases and larger droplets. Multiclone: improved over single cyclones but still limited for submicron sizes. Common Pitfalls: Equating pressure drop with efficiency universally. For submicron control, charging and electrostatic migration outperform inertial devices at reasonable energy cost. Final Answer: Electrostatic precipitator

Question 17

Carbon monoxide air quality: With a TLV under 50 ppm, which source contributes the largest share of carbon monoxide in ambient urban air under typical conditions?

Accepted Answer

Introduction: Carbon monoxide, abbreviated as CO, is a colorless, odorless gas formed by incomplete combustion. Understanding primary sources informs monitoring, standards, and control strategies. The question references a threshold limit value under 50 ppm and asks for the main ambient source, particularly relevant to urban air quality management. Given Data / Assumptions: Urban or peri urban settings with traffic. Conventional internal combustion fleets without universal zero emission replacement. Background photochemistry present but not dominant compared to direct emissions. Concept / Approach: CO forms when carbon containing fuels do not fully oxidize to CO2. Gasoline engines, especially during cold start, rich fueling, or poor maintenance, generate significant CO. While industries emit pollutants, their CO contribution is generally smaller compared to the aggregated vehicle fleet in cities. Domestic fuels contribute locally but not at the scale of traffic corridors. Step-by-Step Solution: Identify widespread incomplete combustion sources.Quantify relative contributions: urban traffic dominates CO inventories in many cities.Industrial stacks are more associated with NOx, SO2, and particulates than CO dominance.Therefore, automobiles exhaust is the main source under typical urban conditions. Verification / Alternative check: Emission inventory studies consistently show roadway emissions as the leading CO source where large vehicle fleets operate. Ambient CO peaks near busy intersections and during rush hours, matching traffic patterns. Why Other Options Are Wrong: Industrial chimney exhaust: not the dominant CO source in most cities. Photochemical reactions: CO can form secondarily but is minor compared to direct tailpipe emissions. Domestic fuel burning: localized and smaller scale than traffic. Natural soils: minor background source. Common Pitfalls: Confusing CO with NOx or SO2 source dominance. Traffic control measures reduce CO significantly through improved combustion and catalytic converters. Final Answer: Automobiles exhaust

Question 18

Occupational health: Inhalation of respirable crystalline silica dust most commonly leads to which clinical outcomes?

Accepted Answer

Introduction: Crystalline silica exposure is a classic occupational hazard in mining, construction, and foundries. The primary disease is silicosis, a fibrotic lung condition. The clinical picture includes breathlessness and a heightened risk of certain infections. Recognizing the correct outcomes supports prevention and surveillance programs. Given Data / Assumptions: Exposure to respirable crystalline silica, not inert dust. Chronic or significant exposure scenarios. No respiratory protection assumed for the risk discussion. Concept / Approach: Silica particles lodge in the alveoli and trigger inflammation and fibrosis. Fibrotic change reduces lung compliance and gas exchange, leading to progressive shortness of breath. In addition, silica impairs macrophage function and predisposes to infections, notably tuberculosis, due to compromised cellular immunity within the lung. Step-by-Step Solution: Identify hallmark disease: silicosis with fibrotic nodules.Link fibrosis to dyspnea: scarring reduces pulmonary capacity and causes breathlessness.Recognize infection risk: silica exposure increases susceptibility to tuberculosis.Thus, both shortness of breath and tuberculosis correctly describe outcomes. Verification / Alternative check: Occupational health guidance emphasizes periodic chest imaging and TB screening in silica exposed workers, confirming both mechanisms of harm. Why Other Options Are Wrong: Asphyxiation: silica does not displace oxygen like inert gases. Options naming only one effect are incomplete. Metal fume fever is linked to zinc oxide fumes, not silica dust. Common Pitfalls: Assuming silicotic lungs recover after exposure stops. Fibrosis is largely irreversible, so prevention through dust control and respirators is critical. Final Answer: Both shortness of breath and tuberculosis

Question 19

Atmospheric terminology: What is smog in the context of urban air pollution episodes?

Accepted Answer

Introduction: Smog is a widely used term in air quality discussions. Understanding what the term captures helps interpret weather advisories and health alerts. Historically, the word blends the ideas of smoke and fog, and modern usage often distinguishes between classical smoke based smog and photochemical smog dominated by secondary oxidants. Given Data / Assumptions: Urban setting with emissions and humidity. Public health context of visibility reduction and irritants. General atmospheric science definitions. Concept / Approach: Classical smog arises when smoke particulates from combustion mix with fog droplets under stagnant, cool conditions, worsening visibility and irritation. Modern photochemical smog, common in sunny cities, forms when NOx and volatile organics react under sunlight to create oxidants such as ozone and peroxyacyl nitrates, often still accompanied by fine particles and haze. The core etymology remains a blend of smoke and fog, which the option captures succinctly. Step-by-Step Solution: Recall origin: smoke plus fog.Relate to episodes: temperature inversions can trap pollutants near the ground.Note evolution: modern smog includes secondary chemistry but still coexists with particulate haze.Therefore, the correct definition is a combination of smoke and fog. Verification / Alternative check: Air quality literature and historical accounts of London type smog confirm the smoke and fog blend, while Los Angeles type smog adds photochemical oxidants to the mix. Why Other Options Are Wrong: Solid particle or liquid particle only options are incomplete. Black smoke alone ignores the fog component. Pure water mist excludes pollutants and does not match health impacts. Common Pitfalls: Assuming smog always looks black. Photochemical smog can appear brownish due to NO2 and oxidants. Final Answer: A combination of smoke and fog

Question 20

Stratospheric protection: Harmful ultraviolet radiation from the sun is largely absorbed by which atmospheric layer or constituent high above the earth surface?

Accepted Answer

Introduction: Incoming solar radiation spans ultraviolet, visible, and infrared wavelengths. Ultraviolet radiation at shorter wavelengths can damage biological tissues and DNA. Earth enjoys natural protection due to a specific atmospheric constituent concentrated in the stratosphere known as the ozone layer. Given Data / Assumptions: Reference to high altitude absorption. Concern is harmful ultraviolet band. Focus on the dominant absorber for UVB and part of UVC reaching the upper atmosphere. Concept / Approach: Ozone, represented as O3, exhibits strong absorption bands in the ultraviolet region. Stratospheric ozone between roughly 15 km and 35 km altitude forms the ozone layer that filters much of the UVB and nearly all UVC before it reaches the surface. Variations in ozone concentration affect the amount of UV reaching the ground and thereby influence health and ecosystems. Step-by-Step Solution: Identify the absorber for UV: ozone molecules in the stratosphere.Clarify altitude: high above the troposphere, in the stratosphere, not a generic gas layer.Confirm that CO2 primarily affects infrared absorption and climate, not UV shielding.Therefore the correct answer is the ozone layer. Verification / Alternative check: Measurements of total column ozone and the ozone hole in polar regions correlate with surface UV index, confirming its shielding role. Why Other Options Are Wrong: Hydrogen and argon layers are not meaningful UV shields. Carbon dioxide absorbs in infrared bands. None of these is incorrect because ozone is the specific absorber. Common Pitfalls: Confusing greenhouse gas effects with UV protection. Greenhouse gases trap heat but do not provide the UV shielding function of ozone. Final Answer: Ozone layer

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