Workplace air quality testing: how it works

Workplace air quality testing measures carbon dioxide, PM2.5, VOCs, temperature and relative humidity in the rooms people actually work in, then compares each reading to the air outside. Done once, it describes a single morning. Done continuously, it shows whether a conference room that feels thick by the second meeting is a pattern or a one-off.

A facilities manager usually hears about it secondhand, in an email that says the air on the third floor feels stale by mid afternoon, or a complaint logged after a long meeting in a windowless room. None of that settles anything on its own. A number does.

This post covers what workplace air quality testing measures, the difference between a one-time test and ongoing monitoring, where to put a monitor in an office, what the numbers mean, and what to try once one of them moves.

Key Takeaways

• Workplace air quality testing covers five readings: CO2 in ppm, PM2.5 in µg/m³, VOCs, temperature in °F and relative humidity in %, each checked against the air outside.
• CO2 above roughly 1,000 ppm in an occupied room is the common sign that outdoor air ventilation hasn't kept up, per ASHRAE's position.
• A one-time test only describes the day it ran. Continuous monitoring catches the afternoon spike or the Monday-meeting spike a spot check misses.
• A good PM2.5 reading stays under 9.0 µg/m³ as a daily average, the top of the EPA's Good band for fine particles.
• A reading tells a facilities team what is happening in a room. It does not adjust a damper or fix a leak by itself.

What workplace air quality testing actually measures

"Air quality" at work is not one number. It is a handful of separate readings, each answering a different question:

• CO2 (ppm): how stale a room is getting, which tracks outdoor air ventilation more than anything burning or off-gassing.
• PM2.5 (µg/m³): fine particles from a shared kitchen, nearby traffic, wildfire smoke or renovation dust.
• VOCs: off-gassing from new paint, flooring, furniture and cleaning products.
• Relative humidity (%): too high and surfaces stay damp long enough for mold; too low and a room gets dry and irritating.
• Temperature (°F): comfort, and a sanity check on whether the HVAC system is keeping pace with the room.
• The air outside: every indoor reading means more set against the outdoor number for that day.

No single reading stands in for the others. A room can read clean on PM2.5 and climb on CO2 the whole time, and the fix for one is not the fix for the other.

A one-time test versus ongoing monitoring

Workplace air quality testing has traditionally meant a single visit: a consultant brings handheld instruments, takes a reading in a few rooms, and leaves with a report. That snapshot is useful for a baseline, but a room on a quiet Tuesday morning reads nothing like the same room during a packed Monday staff meeting.

Continuous monitoring answers a different question: not "what did the air measure once," but "what does this room do over a normal week." A CO2 line that climbs every day after the 10 a.m. meeting and drops at lunch is a pattern a facilities team can plan a ventilation schedule around. A single spot check would never show it.

Where to put a monitor in an office

A monitor belongs in the room, not in a hallway meant to represent the whole floor. A glass-walled conference room near the elevator bank, an open floor section with 40 desks, and a small room next to the shared kitchen rarely read the same on the same afternoon, so one reading for the whole floor hides whichever of those is actually the problem.

Where it sits inside the room matters too. Set it away from the supply vent and any open window, roughly at head height for someone sitting at a desk, not mounted up near the ceiling where the air has already mixed with whatever the HVAC system is pushing out. A room that was just painted or recarpeted is worth a reading on its own, since new paint, flooring and furniture keep off-gassing VOCs for weeks after the crew leaves.

What the readings mean, and where the thresholds come from

CO2 is the most useful single reading for ventilation, because it tracks occupancy and fresh air in one number. Outdoor air runs close to 420 ppm, and ASHRAE's position is that indoor CO2 should stay within about 700 ppm of that level, putting the practical ceiling at roughly 1,100 ppm. Past that, most people start calling a room stuffy whatever the thermostat says.

PM2.5 is judged against the air outside the building that day. A good indoor reading stays under 9.0 µg/m³ as a daily average, the top of the EPA's Good band. On a wildfire smoke day, indoor PM2.5 tracks roughly 55% to 60% of the outdoor level once windows and doors stay shut, so a smoky day outside still moves the indoor number.

Relative humidity has a wider comfortable range. The EPA's guidance keeps it under 60%, with 30% to 50% recommended, to avoid the condensation that lets mold take hold.

What to do when a reading climbs

A reading points at the problem. Somebody still has to fix it, and the fix depends on which number actually moved.

If CO2 is the one climbing, the building's ventilation schedule is the first thing to check. Many offices run the outdoor air damper on a fixed schedule built around a typical workday, so a room that fills up for an early meeting or stays busy past 6 p.m. can run short of fresh air the schedule never accounted for. Widening that schedule, or just increasing outdoor air during occupied hours, is usually the fix.

If PM2.5 is the one climbing, check the obvious thing first: are the windows and doors actually shut on a smoke day. Past that, a MERV 13 filter only helps while the fan is moving enough air through it, which is worth confirming rather than assuming.

If humidity is the one climbing, look for where the water is coming from, a roof leak, a door that doesn't seal, a bathroom fan that stopped working, before reaching for a dehumidifier. A reading that stays high after that fix means the source wasn't the one that got found.

Workplace air quality testing in multi-tenant buildings

A multi-tenant building adds a wrinkle a single-tenant office doesn't have: a complaint on one floor doesn't tell you anything about the floor below it, and a property manager often has to answer for a space they don't occupy themselves. The same logic from indoor air quality testing in schools applies here: one monitor per occupied space, kept running, not a single walkthrough.

When a tenant says a floor is stuffy, a continuous reading gives a property manager a third option besides sending someone up to look or reassuring the tenant over email. Pull up the CO2 and PM2.5 history, check it against the outdoor air for that period, and either adjust the ventilation schedule or show the tenant the room was within range the whole time. Either way, the answer is a number, and the record is still there the next time it comes up.

FAQ

What is workplace air quality testing? Workplace air quality testing measures CO2, PM2.5, VOCs, temperature and relative humidity in the rooms people occupy, checked against the air outside. It can be a single site visit or continuous monitoring; the two answer different questions.

How often should an office test its air quality? An office is better served by a monitor that stays in the room than a test scheduled once a quarter. A quarterly test might land on a slow Tuesday and miss the Monday pattern entirely, while a monitor left running catches the afternoon climb as it happens, every day it happens.

What is a good CO2 level for an office? A good CO2 level for an office stays under roughly 1,000 to 1,100 ppm, the range ASHRAE treats as a sign that outdoor air ventilation is keeping up with occupancy.

Does opening a window fix stuffy air at work? Opening a window lowers CO2 by bringing in outdoor air, and it is often the fastest fix in a room with operable windows. In a sealed building, the equivalent fix is increasing outdoor air through the HVAC system during occupied hours.

Who is responsible for air quality testing in a commercial building? Responsibility usually sits with whoever manages the building, the property manager or facilities team, even when the complaint comes from a tenant who occupies only one floor. A continuous reading gives that team evidence before the next complaint, not just after it.

The next step for a facilities team

There is no single pass or fail score for workplace air quality testing. There is CO2, PM2.5, VOCs and humidity, each read room by room against the outdoor air for that day, and each one pointing to a different fix. A conference room past 1,100 ppm of CO2 needs a ventilation schedule that matches when people actually use it. A building that lets PM2.5 past 9.0 µg/m³ on a smoke day needs its windows checked and its filter confirmed, not assumed. A floor sitting above 50% humidity for weeks needs someone to go find the leak.

A facilities team that would rather have that evidence before the next complaint than after it can start with a short form on Measured Air's page for commercial buildings. Measured Air replies within a business day.