Workplace Office CO₂

Office IAQ: the 4 p.m. conference-room problem

A typical office starts at outdoor CO₂ baseline and ends the day at 1,200 ppm in the meeting rooms. Plus VOCs from cleaning and new furniture, plus whatever the outdoor air brings in.

Updated 2026-05-26 2 min read

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An open-plan office in late afternoon with a glass-walled conference room in the background and a Terrestream sensor on a desk.
Photo: Thirdman via Pexels
demographic-band Interactive chart - coming soon
Office CO₂ trajectory through the workday: 450 ppm at 7 a.m., 900-1,500 ppm by 4 p.m. in conference rooms.

A commercial office is a more predictable IAQ environment than a home, and a worse-performing one for most occupants. CO2 follows a stereotyped curve: 420-450 ppm at 7 a.m. when the building wakes up, climbing through the morning as people arrive, peaking in conference rooms in mid to late afternoon at 900-1,500 ppm or higher. The ASHRAE 62.1 ventilation rate for offices (5 cfm/person of outside air plus 0.06 cfm per square foot) is calibrated to keep steady-state CO2 around 1,000 ppm, which the Allen 2016 COGfx study already shows costs 15% of cognitive function versus a 600 ppm baseline.

VOC sources in offices look different from homes. Industrial cleaning products on a contractor schedule (evening or early morning) hit a building at predictable times. Toner, fuser oil, and ozone from laser printers spike on a desk near a high-volume printer. New furniture, new carpet, and new partition systems off-gas formaldehyde and other VOCs for weeks to months after installation, and the building rarely smells of it after the first few days even though the readings persist. Formaldehyde in particular peaks in newly built-out tenant spaces. Old buildings have the opposite problem: residual ETS, deteriorating mastics and adhesives, and HVAC ductwork that has not been cleaned in a decade.

PM and the outdoor-air story matter more than most office workers realize. The intake plenum sits on a roof or the side of the building, often near a parking-garage exhaust, a loading dock, or a major street. WELL Building certified spaces require MERV-13 minimum on the supply side; many non-certified buildings still run MERV-8, which lets most PM2.5 through. On wildfire smoke days and during high-pollen or ozone events the building can become a worse environment than the sidewalk outside if the intake filtration is undersized.

What an individual employee can do: ask facilities for the most recent IAQ assessment and the supply-air MERV rating (most facilities teams will share these). Crack a window if your floor has openable ones, particularly during midday breaks. Schedule cognitively demanding meetings before 1 p.m. when conference-room CO2 is still recoverable. A personal HEPA at the desk (sized per CADR) handles PM2.5 in your immediate breathing zone independently of building HVAC. For the building-level story see demand-controlled ventilation, which is how most modern offices should be (and are not) running.

References

  1. ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality www.ashrae.org
  2. Allen et al. - COGfx ventilation and cognition study doi.org
  3. WELL Building Standard - Air concept standard.wellcertified.com
  4. EPA - Indoor air quality basics www.epa.gov

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