Indoor Air Quality Questions and Answers

Answer: C

Correct answer: False, outdoor air may be more polluted than the indoor air

Ventilation dilutes towards the outdoor concentration, so it helps only when the outdoor air is cleaner. During a smog episode, near heavy traffic, in wildfire smoke or on a high pollen day, opening a window raises the indoor concentration.

The response then is to keep windows shut and filter recirculated air. Energy is a real cost too, but it is not the reason the statement fails - the failure is that ventilation cannot beat the air it brings in.

Answer: D

Correct answer: It is caused by a single identified agent

That is the defining absence. Sick building syndrome is the diagnosis of exclusion: symptoms occur in a building and ease on leaving it, and investigation finds no specific agent.

Where an agent is identified - legionella, carbon monoxide, an allergen - the condition is a building related illness instead. The other three statements are all true of the syndrome: non-specific symptoms, relief on leaving, and an association with poor ventilation.

Answer: A

Correct answer: No, radon is a gas that the filter does not capture

A HEPA filter removes particles, and radon is a noble gas. It passes through untouched however long the unit runs and whatever the flow.

The filter does capture the solid decay products attached to airborne particles, which is not useless - those deliver the lung dose - but the radon remaining generates more continuously, so the benefit is partial and temporary. Preventing entry, by sealing and sub-slab depressurisation, is the control that addresses the source.

Answer: B

Correct answer: Raising indoor humidity

Mites absorb water vapour from the air, so raising humidity is exactly what allows the population to thrive. Below about 50 per cent they cannot maintain their water balance.

The other three all help: removing carpets takes away a major reservoir of mites and accumulated allergen, holding humidity below half prevents the population sustaining itself, and washing bedding at high temperature kills mites and removes allergen from the place of longest exposure.

Answer: C

Correct answer: No, it is used as a surrogate for ventilation adequacy

Indoor levels of one to two thousand parts per million are not harmful. Carbon dioxide is measured because occupants produce it at a predictable rate, so its excess over outdoor indicates the outdoor air supplied per person.

A high reading matters for what it implies: everything else occupants emit is being diluted just as poorly. It is easily and cheaply measured, which is what makes it a practical proxy for a ventilation rate that would otherwise need a tracer gas test.

Answer: D

Correct answer: The steady concentration is proportional to the room volume

Volume does not appear in the steady state at all. The balance is

\[ C = C_{out} + \frac{G}{Q} \]

so only the outdoor concentration, the source strength and the ventilation flow determine it.

The other three statements are true, including the role volume does play: it sets the time constant \( V/Q \) governing how quickly the steady value is approached. Volume affects the dynamics, not the equilibrium.

Answer: A

Correct answer: False, the moisture causing the growth must be dealt with first

Mould needs water, and the nutrients it needs are already present everywhere in a building. A biocide kills the visible colony but leaves the moisture that produced it, so growth returns - often within weeks.

Dead spores also remain allergenic, so killing without removing achieves less than it appears. The order is: find and fix the water, dry the fabric, then remove the growth. Biocide toxicity is a secondary consideration rather than the reason.

Answer: B

Correct answer: Sick building syndrome

A building related illness has an identified agent and a clinical diagnosis, which is exactly what sick building syndrome lacks - non-specific symptoms relieved by leaving the building, with no cause found.

The other three qualify: carbon monoxide poisoning with a measurable gas and a blood test, legionnaires' disease with an identified organism, and hypersensitivity pneumonitis with a demonstrable immune response to a known exposure. The presence or absence of an agent is the whole distinction.

Answer: C

Correct answer: No, adsorption acts on molecules rather than on particles

Activated carbon works by adsorbing gas molecules onto its very large internal pore surface. Particles are orders of magnitude too large to enter those pores.

Depth of bed does not help, since the mechanism is wrong rather than insufficient, and pressure drop is a practical matter rather than the reason. Removing particulate needs a mechanical filter, which is why an air cleaner intended for both carries a particulate stage and a carbon stage in series.

Answer: D

Correct answer: Sealing the kitchen to prevent draughts

Sealing the kitchen removes the ventilation that was diluting the smoke, so the concentration rises - the opposite of what is wanted.

The other three all reduce exposure, by three different routes: a flue removes the combustion products at source, better combustion produces less to remove, and switching to gas or electricity eliminates the source almost entirely. The last is the most effective by a wide margin, which is the argument for fuel switching over stove improvement.