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What parameters does the AirGradient ONE measure?

This page explains what each parameter means, why it is measured that way, and how frequently data is recorded.

For a more detailed list refer to: https://github.com/airgradienthq/arduino/blob/master/docs/local-server.md

Time Resolution

  • Wi-Fi model: 1-minute intervals

  • Cellular model: 3-minute intervals

Particulate Matter (PM)

PM2.5 (µg/m³) – Raw (cf_atm)

Description: Raw, uncorrected mass concentration of airborne particles ≤ 2.5 µm.
Why µg/m³? Micrograms per cubic meter represents the total mass of inhalable particles in a given air volume. This is the global standard used in air quality regulations and guidelines.

PM2.5 (µg/m³) – Corrected

Description: PM2.5 value adjusted using the calibration formula selected in the dashboard.
Why corrected? Calibration formulas compensate for sensor characteristics and environmental factors to improve real-world accuracy.

PM1 (µg/m³)

Description: Mass concentration of particles ≤ 1 µm.
Why µg/m³? Provides a mass-based measure of very fine particles, which can penetrate deeply into the lungs.

PM10 (µg/m³)

Description: Mass concentration of particles ≤ 10 µm.
Why µg/m³? Indicates larger respirable particles such as dust.
Note: Optical sensors are optimized for PM2.5. PM10 values are less reliable. Very large particles (e.g., pollen >10 µm) are generally not detected.

PM 0.3 µm Particle Count (per dL)

Description: Number of particles ≥ 0.3 µm, measured as number concentration.
Why particle count? Particle count tracks the number of particles regardless of mass. Small particles may be high in number but low in weight, so count-based metrics can reveal events mass-based PM values may miss.

Other extended Particle Count measures available on request:

  • Particle count 0.5µm per dL

  • Particle count 1.0µm per dL

  • Particle count 2.5µm per dL

  • Particle count 5.0µm per dL 

  • Particle count 10µm per dL

Carbon Dioxide (CO₂)

CO₂ (ppm) – Raw

Description: Measured carbon dioxide concentration.
Why ppm? Parts per million reflects volumetric gas concentration and is the standard unit for tracking indoor CO₂ buildup from human activity.

Temperature & Humidity

Temperature (°C) – Raw

Description: Ambient temperature near the sensor.
Why °C? Direct physical measurement affecting comfort and sensor performance.

Indoor monitors: Raw temperature closely reflects room conditions.
Outdoor monitors: Raw temperature may diverge from true ambient because the sensor sits inside the enclosure. Corrected values compensate for this.

Temperature (°C) – Corrected

Description: Temperature adjusted using a calibration formula.
Why corrected? Improves ambient accuracy, especially for outdoor units.

Humidity (%) – Raw

Description: Ambient relative humidity near the sensor.
Why % RH? Relative humidity expresses water vapor content relative to saturation. It influences comfort, condensation, and sensor behavior.

Outdoor monitors: Raw values may diverge due to enclosure effects; corrected values compensate for this.

Humidity (%) – Corrected

Description: Relative humidity adjusted using a calibration formula.
Why corrected? Improves ambient accuracy for outdoor deployments.

Heat Index (°C)

Description: Calculated apparent temperature combining corrected temperature and humidity.
Why calculated? Reflects how hot it actually feels when humidity is considered.

VOC (Volatile Organic Compounds)

TVOC (ppb)

Description: Total VOC concentration converted to ppb using Sensirion’s formula.
Why ppb? Reported in parts per billion for familiarity, but this is a relative estimate derived from the VOC index — not an absolute concentration.

TVOC Index (1–500)

Description: Scaled index representing total VOC activity.

  • 100 = baseline

  • >100 = more VOCs than recent 24-hour baseline

  • <100 = fewer VOCs than baseline

Why an index? MOx sensors respond broadly to many VOCs. Exact ppb estimates are unreliable, so a unitless index is better for detecting trends.

Adaptive behavior:

  • In clean air → becomes more sensitive to small changes

  • In polluted air → reduces sensitivity to avoid saturation

TVOC Raw log(R)

Description: Logarithmic raw resistance output from the MOx sensor.
Why log(R)? MOx sensors measure resistance changes of a heated metal oxide surface.

  • Reducing gases (VOCs) → decrease resistance

  • Oxidizing gases → increase resistance

  • Output is broadband and non-specific.

NOx (Nitrogen Oxides)

NOx Index (1–500)

Description: Scaled index representing oxidizing gas activity.

  • 1 = baseline

  • >1 = increased oxidizing gases

Why an index? Similar to VOC, MOx sensors detect general oxidizing gases rather than specific compounds.
Note: The NOx index does not use adaptive gain like the VOC Index

NOx Raw log(R)

Description: Logarithmic raw resistance from the NOx MOx sensor.
Why log(R)? Resistance increases in presence of oxidizing gases such as NOx. Output reflects general oxidizing gas presence rather than specific concentrations.

 

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