---
title: "Formaldehyde (CH₂O) Sensors & Limit Values | Aethair"
description: "Formaldehyde (CH₂O) is a colorless, pungent gas and a common indoor air pollutant. Limit values from WHO, OSHA, NIOSH, and LEED, plus sensors that measure it."
url: https://aethair.io/parameters/ch2o/
---

Measurements · Gases & VOCs

# Formaldehyde (CH₂O)

Also known as HCHO, CH2O, formaldehyde monitor

Formaldehyde (CH₂O/HCHO), a colorless carcinogenic VOC emitted by pressed-wood products, insulation, furnishings, and combustion; a key indoor air quality parameter.

[Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Formaldehyde (CH₂O) Monitoring](https://aethair.io/build/?params=ch2o)

At a glance

mg/m³ Gases & VOCs

2 ways to measure it

- **Aethair IAQ** Built-in sensor
- **Aethair PRO** 1 cartridge

6 standards set limits

- [WELL WELL v2](https://aethair.io/resources/well-building-standard-air-quality/)
- [WHO WHO indoor 2010](https://aethair.io/standards/who_iaq_2010/)
- [AQMD SCAQMD 1180](https://aethair.io/standards/scaqmd_1180/)
- [NIOSH NIOSH REL](https://aethair.io/standards/niosh_rel/)
- [OSHA OSHA formaldehyde](https://aethair.io/standards/osha_formaldehyde/)
- [LEED LEED v5](https://aethair.io/standards/leed_v5/)

What it is

## What is formaldehyde (CH₂O)?

Formaldehyde is a colorless gas with a sharp, pungent odor, and one of the most common and well-studied indoor air pollutants. Its dominant indoor source is off-gassing from pressed-wood products (particleboard, plywood, and MDF bound with urea-formaldehyde resins), along with insulation, laminate flooring, textiles, adhesives, and combustion, including tobacco smoke. Emissions are highest when materials are new and rise with temperature and humidity, so formaldehyde is a particular concern in newly built, newly furnished, and warm, humid interiors.

Although it is technically a VOC, formaldehyde is measured and regulated in its own right because it is both especially common indoors and especially hazardous.

### Health and operational effects

Formaldehyde irritates the eyes, nose, and throat at low concentrations and can trigger coughing, wheezing, and allergic sensitization. Critically, it is classified as a human carcinogen (linked to nasopharyngeal cancer and leukemia), which is why health agencies set guideline values low and why a total-VOC reading is not an adequate substitute for measuring it directly.

For building owners, manufacturers, and schools the operational stakes include occupant-complaint response, compliance with product-emission standards, and the growing set of healthy-building certifications that call out formaldehyde specifically. New modular and manufactured buildings are a recurring hot spot.

Limits

## Formaldehyde (CH₂O) Limit Values

The published values, by averaging period; each links to the standard that sets it.

8-hour TWA (PEL)

[**0.75 ppm** OSHA formaldehyde](https://aethair.io/standards/osha_formaldehyde/)

1-hour, notification threshold

[**44 ppb** SCAQMD 1180](https://aethair.io/standards/scaqmd_1180/)

A01 Air Quality

[**50 µg/m³** WELL v2](https://aethair.io/resources/well-building-standard-air-quality/ "verified by laboratory testing of occupiable spaces")

30-minute

[**0.1 mg/m³** WHO indoor 2010](https://aethair.io/standards/who_iaq_2010/ "formaldehyde guideline value")

TWA

[**0.016 ppm** NIOSH REL](https://aethair.io/standards/niosh_rel/ "carcinogen")

Ceiling

[**0.1 ppm** NIOSH REL](https://aethair.io/standards/niosh_rel/ "15-minute")

STEL

[**2 ppm** OSHA formaldehyde](https://aethair.io/standards/osha_formaldehyde/ "15-minute")

Action level

[**0.5 ppm** OSHA formaldehyde](https://aethair.io/standards/osha_formaldehyde/ "8-hour TWA")

One-time test

[**16 ppb** LEED v5](https://aethair.io/standards/leed_v5/ "20 µg/m³")

- **WELL v2** 50 µg/m³: verified by laboratory testing of occupiable spaces
- **WHO indoor 2010** 0.1 mg/m³: formaldehyde guideline value
- **NIOSH REL** 0.016 ppm: carcinogen
- **NIOSH REL** 0.1 ppm: 15-minute
- **OSHA formaldehyde** 2 ppm: 15-minute
- **OSHA formaldehyde** 0.5 ppm: 8-hour TWA
- **LEED v5** 16 ppb: 20 µg/m³

Formaldehyde is reported in mg/m³ or ppb. The WHO indoor air quality guideline of 0.1 mg/m³ over 30 minutes is the widely cited health-based reference and is designed to prevent both irritation and longer-term risk. Because emissions decay as materials age but rebound in heat and humidity, interpret a reading in the context of building age and conditions. Treat a sustained exceedance, not a brief spike, as the trigger for source control and increased ventilation.

How it is measured

## How Formaldehyde (CH₂O) Is Measured

Continuous monitoring generally uses an **electrochemical sensor** tuned to formaldehyde, which produces a current proportional to concentration, or a specialized photometric sensor. These give real-time readings suitable for building monitoring. Because generic metal-oxide TVOC sensors respond to many compounds at once, they cannot reliably isolate formaldehyde; a dedicated sensor is needed for a trustworthy CH₂O value. Laboratory reference methods use active sampling onto DNPH cartridges followed by chromatographic analysis.

Built into Aethair IAQ 1

Measured by the monitor's own sensors, calibrated before it ships: nothing to add.

Aethair PRO cartridge 1

A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair MultiSense.

### Placing formaldehyde sensors

Monitor in the occupied breathing zone of spaces with significant pressed-wood content: bedrooms, offices, classrooms, and newly fitted-out areas. Since emissions climb with temperature and humidity, readings taken in warm, still conditions represent a realistic worst case; pairing formaldehyde with temperature and humidity helps interpret why levels move.

### Every device and option that measures Formaldehyde (CH₂O) 2

| Device / option | Type | Base platform | Measures |
| - | - | - | - |
| **Aethair IAQ built-in sensors** | Built-in sensors | Aethair IAQ | Formaldehyde (CH₂O) [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Particle Count (by size)](https://aethair.io/parameters/particle_count/) [PM1](https://aethair.io/parameters/pm1/) |
| **Aethair MultiSense** `0d09` | MultiSense cartridge | Aethair PRO | Formaldehyde (CH₂O) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Illuminance / Light](https://aethair.io/parameters/light/) |

[Configure Formaldehyde (CH₂O) Monitoring](https://aethair.io/build/?params=ch2o)

Where it is monitored

## Solutions That Monitor Formaldehyde (CH₂O)

Each one links to the solution page showing what that industry measures it for.

### [Healthcare Air Monitoring](https://aethair.io/solutions/healthcare/)

Often added Clinical air quality, pressurization, and patient safety

### [Indoor Air Quality](https://aethair.io/solutions/iaq-monitoring/)

Often added Offices, schools, homes, and public buildings

### [School Air Monitoring](https://aethair.io/solutions/education/)

Often added Classroom CO₂, particulates, and campus IAQ

Article Library

## Reading on Formaldehyde (CH₂O)

### [WELL Building Standard Air Quality: CO2 & PM2.5 Limits 2026](https://aethair.io/resources/well-building-standard-air-quality/)

WELL v2 air quality limits: PM2.5 at 15 µg/m³, formaldehyde at 50 µg/m³, CO2 at 900 ppm for ventilation monitoring, plus the monitoring WELL verifies.

### [IAQ Monitoring Parameters: PM2.5, CO2, VOCs & Formaldehyde](https://aethair.io/resources/indoor-air-quality-monitoring-parameters/)

Indoor air quality monitoring parameters explained: PM2.5, CO2, VOCs, and formaldehyde, plus the sensors, thresholds, and OSHA, ASHRAE 62.1, and WELL limits.

### [Commercial Building IAQ Monitoring: ASHRAE 62.1 & WELL](https://aethair.io/resources/indoor-air-quality-monitoring-commercial-buildings/)

Indoor air quality monitoring for commercial buildings: what to measure, which standards apply, and how property managers build a program tenants trust.

### [Ambient Air Quality Monitoring: What Nonattainment Changes](https://aethair.io/resources/ambient-air-quality-monitoring/)

Ambient air quality monitoring explained: how PM2.5 attainment is measured, what a nonattainment designation triggers, and what site-level monitoring adds.

### [ASHRAE 170 Requirements and Which Edition Applies to You](https://aethair.io/resources/ashrae-170-requirements/)

ASHRAE 170 requirements explained: what the standard sets, which edition your facility is held to, what changed in 2025, and how each value gets verified.

### [Ozone Exposure Limits and Monitoring: OSHA and NAAQS](https://aethair.io/resources/ozone-monitoring-exposure-limits/)

OSHA's ozone PEL is 0.1 ppm as an 8-hour TWA. How NIOSH, ACGIH, and the 70 ppb NAAQS compare, and why ozone needs short-interval monitoring.

[All articles](https://aethair.io/resources/)

Related

## More in Gases & VOCs

[Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [VOC (Total)](https://aethair.io/parameters/voc/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Carbon Monoxide (CO)](https://aethair.io/parameters/co/) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Oxygen (O₂)](https://aethair.io/parameters/o2/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Nitric Oxide (NO)](https://aethair.io/parameters/no/) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Combustible (LEL)](https://aethair.io/parameters/lel/) [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/)

Questions

## Formaldehyde (CH₂O) FAQ

Why measure formaldehyde separately from TVOC?

Formaldehyde is a carcinogen with a low health-based guideline, and generic total-VOC sensors cannot isolate it from the dozens of other compounds they respond to. A dedicated formaldehyde sensor gives a specific, trustworthy CH₂O value that a TVOC number cannot.

What is a safe level of formaldehyde indoors?

The WHO guideline is 0.1 mg/m³ (about 80 ppb) averaged over 30 minutes, set to prevent sensory irritation and longer-term cancer risk. Levels are typically highest in new or newly furnished spaces and fall as materials age.

Why are my formaldehyde levels higher in summer?

Formaldehyde off-gassing increases with temperature and humidity, so the same materials emit more in warm, humid conditions. This is why monitoring alongside temperature and humidity is useful, and why readings in hot, still rooms represent a realistic worst case.

How can I monitor formaldehyde?

The Aethair IAQ measures formaldehyde with a built-in sensor, and the Aethair PRO with the MultiSense cartridge in its MultiSense socket, for indoor air quality programs. Use the configurator to combine CH₂O with PM2.5, CO₂, and TVOC for a full indoor-air panel, or pair a Thiamis gateway with a specialized analyzer for higher-accuracy work.