Why is carbon dioxide measured indoors, and what does it actually tell you?
Carbon dioxide indoors is not a poison at household levels — it is a proxy for ventilation, and a reliable one. Bedroom studies find measurable losses in sleep quality above roughly 750 to 800 ppm, and losses in next-day cognitive performance at higher levels. Most consumer monitors do not measure it directly.
Key facts
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Bedroom carbon dioxide above roughly 800 ppm is associated with measurably worse sleep quality.
Review of 17 studies and 22 experimental datasets, ASHRAE 1837-RP, 2025.
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At 1,300 ppm rather than 750 ppm, sleepers spent 7.8 minutes longer awake and showed reduced deep sleep.
Field-lab crossover, 36 healthy adults, Building and Environment, 2023.
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The Good band of the indoor index used in Dubai ends at 600 ppm of carbon dioxide.
Environmental Indoor Air Quality Index v1.0, pollutant breakpoints table.
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Most consumer air monitors report an estimated eCO2 derived from a chemical sensor rather than a direct infrared measurement.
Sensor datasheets; the distinction between metal-oxide eCO2 and NDIR measurement.
What does carbon dioxide indoors actually indicate?
Carbon dioxide indoors is a proxy measurement. People exhale it continuously, so in an enclosed space with limited fresh air it accumulates in proportion to how many people are present and how little outdoor air is arriving. The concentration is therefore an index of ventilation rather than a hazard in its own right.
This is why carbon dioxide appears on indoor air quality frameworks alongside genuine pollutants. Guidance documents describe it as one of the most practical investigative tools available for establishing whether an occupied space is adequately ventilated. Its acute effects at indoor levels are listed as difficulty concentrating, drowsiness and increased respiration rate — not the toxicity associated with the other parameters.
The useful consequence is that a bedroom's carbon dioxide curve overnight is a direct read on that room's air exchange, without any need to measure airflow.
How much does bedroom carbon dioxide affect sleep?
Bedroom carbon dioxide affects sleep measurably, and the effect appears at concentrations most people would not consider high. A field-lab crossover study of 36 healthy adults compared three ventilation levels producing average concentrations of 750, 1,000 and 1,300 ppm. Against the 750 ppm condition, sleep efficiency fell by 1.3 and 1.8 percent respectively, and time spent awake rose by 5.0 and 7.8 minutes. At 1,300 ppm deep sleep duration also decreased, alongside a significant rise in salivary cortisol after waking.
An earlier pair of field interventions in single-occupancy dormitory rooms compared a window open against closed, producing average concentrations of 660 and 2,585 ppm. Objectively measured sleep quality, the perceived freshness of the air, next-day reported sleepiness and ability to concentrate, and performance on a test of logical thinking all improved significantly at the lower concentration.
A 2025 review covering 17 studies and 22 experimental datasets concluded that bedroom ventilation should hold carbon dioxide at or below approximately 800 ppm to avoid disturbed sleep, and that achieving this requires around 8 litres per second per person — at least double what many current residential standards assume.
These are small effect sizes per night. They are also nightly, and cumulative across a school year.
Why do two different sources agree on roughly the same number?
Two separate lines of work converge near 600 to 800 ppm. The indoor index used in Dubai places the ceiling of its Good band for carbon dioxide at 600 ppm, with the Moderate band running to 1,000. The sleep literature finds no measurable effect below about 750 ppm and consistent effects above roughly 1,150.
The convergence is worth noting because the two were derived differently — one from a regulatory framework balancing several pollutants, the other from controlled sleep experiments. Where a regulator and a laboratory arrive separately at nearly the same threshold, the threshold is more likely to be real.
What can a carbon dioxide reading not tell you?
A carbon dioxide reading tells you about ventilation and nothing else. It says nothing about particles, about volatile organic compounds, about formaldehyde, or about mould. A room can be well ventilated and still contain a strong pollutant source; a room can be poorly ventilated and contain nothing worth diluting.
There are two measurement traps. The first is that many consumer monitors do not measure carbon dioxide at all. They report eCO2 — an estimate derived from a metal-oxide sensor responding to volatile organic compounds, then mapped onto a carbon dioxide scale. Such a device will read a cleaning spray as a crowded room. Direct measurement uses nondispersive infrared absorption.
The second is automatic baseline calibration. Many sensors periodically assume that the lowest concentration they have recently seen corresponds to outdoor air, and re-zero accordingly. In a bedroom that never reaches outdoor air, this assumption is false, and the sensor drifts downward over time, reporting calm in a room that is not calm. For this reason the overnight rise is a more trustworthy quantity than the absolute level.
Lower bedroom carbon dioxide tonight
- Open the door properlySleep with the bedroom door open a hand's width, not just off the latch.
- Flush the room in cooler monthsOpen the window for ten minutes before bed and again on waking.
- Keep air moving in summerSet the air conditioning fan to run continuously rather than cycling with the thermostat.
- If the door must stay shutOpen the window a crack instead.
Definitions
- eCO2
- An estimated carbon dioxide value produced by a metal-oxide sensor that actually responds to volatile organic compounds, then mapped onto a carbon dioxide scale. It is not a carbon dioxide measurement and will read a cleaning spray as a crowded room.
- Automatic baseline calibration
- A routine in which a sensor periodically assumes the lowest concentration it has recently seen is outdoor air and re-zeros against it. In a room that never reaches outdoor air the assumption is false and the reported level drifts downward.
- Air change rate
- How many times per hour a room replaces its air, written as air changes per hour. It can be fitted from how quickly carbon dioxide decays once the room empties, which makes it measurable without any airflow instrument.
What we are sure of, and what we are not
Established
- That indoor carbon dioxide at household levels is a ventilation proxy rather than a toxic exposure.
- That bedroom carbon dioxide above roughly 750 to 800 ppm degrades measured sleep quality.
- That the overnight rise is more trustworthy than the absolute level on a sensor with automatic baseline calibration.
Estimated by us
- The air change rates quoted for the monitored bedroom, fitted from carbon dioxide decay rather than measured with an airflow instrument, and drawn from a single room.
Not known
- Whether the effects measured in temperate-climate dormitories transfer unchanged to sealed, air-conditioned Gulf bedrooms with no openable ventilation path.
How the figures on this page were produced
The two nights shown are one monitored Dubai bedroom, nine days apart, with no visit from us in between. The air change rates are fitted from the exponential decay of carbon dioxide after the room empties, taken as the median over accepted decay events in each period rather than from any single night. Absolute concentrations from this sensor are uncalibrated, so the overnight rise and the decay rate are reported rather than the level. One room, one household, published with that household's consent — not a fleet result.
References
Strøm-Tejsen P, Zukowska D, Wargocki P, Wyon DP. The effects of bedroom air quality on sleep and next-day performance. Indoor Air. 2016;26(5):679–686. doi:10.1111/ina.12254 Two field-intervention experiments in single-occupancy dormitories. Reports improved objective sleep quality and next-day logical-thinking performance at lower carbon dioxide. Small samples, n=14 and n=16.
Xu C, Wargocki P et al.. Ventilation causing an average CO2 concentration of 1,000 ppm negatively affects sleep: a field-lab study on healthy young people. Building and Environment. 2023. 36 participants, balanced crossover across 750, 1,000 and 1,300 ppm. Source of the 5.0 and 7.8 minute figures. DOI NOT VERIFIED — flagged in the board.
Akimoto M et al.. New research on bedroom ventilation and sleep quality suggests that building standards should be revisited. Science and Technology for the Built Environment. 2025. ASHRAE 1837-RP review of 17 studies and 22 datasets. Source of the 800 ppm and 8 L/s per person figures. DOI NOT VERIFIED — flagged in the board.
Dubai Municipality. Environmental Indoor Air Quality Index, version 1.0. Technical methodology document. 2025. Pollutant breakpoints table. Source of the 400–600 ppm Good band. Written for buildings and facilities, not residential, and not enforced.
About Gaia Solutions
We measure indoor air in Dubai homes and buildings, treat it with plant-based products, and tend it four times a year. Where we show our own data we state how many rooms, over what period, and with what coverage; our devices are factory-calibrated and we hold no individual calibration certificates, so we publish the shape of a change rather than an absolute concentration judged against a limit.
support@gaia-solutions.earth · +971 56 374 2421 · References & limits →