Why is CO2 used as a surrogate for ventilation adequacy in IAQ assessments?

Why is CO2 used as a surrogate for ventilation adequacy in IAQ assessments?

• A. It correlates with occupancy and ventilation; higher concentrations indicate poorer ventilation.
• B. It directly measures the rate of air exchange per hour.
• C. It is unrelated to occupancy but indicates temperature.
• D. It indicates only outdoor air quality.

Answer: (A)

The main idea is that CO2 levels inside a occupied space rise and fall based on how much people are generating it and how well the space is ventilated. People continually exhale CO2, so the indoor concentration reflects the balance between this generation and the dilution by outdoor air through ventilation. If many people are present and ventilation is insufficient, CO2 builds up; if ventilation is good relative to occupancy, CO2 stays closer to outdoor levels. That makes CO2 a practical signal of ventilation adequacy in real time. Why the other options don’t fit: CO2 doesn’t directly measure the air change rate per hour—it's an indirect indicator that depends on how many people are there and how much they’re producing, plus how well the space is ventilated. It isn’t primarily a temperature indicator, so it doesn’t reflect temperature-related IAQ aspects. And while outdoor air quality can influence CO2, indoor CO2 levels mainly reveal occupancy-driven ventilation performance, not only outdoor conditions.

The main idea is that CO2 levels inside a occupied space rise and fall based on how much people are generating it and how well the space is ventilated. People continually exhale CO2, so the indoor concentration reflects the balance between this generation and the dilution by outdoor air through ventilation. If many people are present and ventilation is insufficient, CO2 builds up; if ventilation is good relative to occupancy, CO2 stays closer to outdoor levels. That makes CO2 a practical signal of ventilation adequacy in real time.

Why the other options don’t fit: CO2 doesn’t directly measure the air change rate per hour—it's an indirect indicator that depends on how many people are there and how much they’re producing, plus how well the space is ventilated. It isn’t primarily a temperature indicator, so it doesn’t reflect temperature-related IAQ aspects. And while outdoor air quality can influence CO2, indoor CO2 levels mainly reveal occupancy-driven ventilation performance, not only outdoor conditions.