AirGradient ONE & Open Air can send the data not only to the AirGradient Cloud, but also to a local or remote MQTT broker. It publishes a JSON payload every 60 seconds.

The payload is sent under the following Topic: airgradient/readings/{{SENSOR SERIAL NR}}. For example: airgradient/readings/34b7daa16674

Protocol and Payload

To enable MQTT via the AirGradient Dashboard, go to General Settings > Select 'Connectivity' tab > Toggle MQTT switch to enable > Input your MQTT Broker URL > Click 'Save MQTT Configuration'

If your broker has a username and password it can be set in this pattern mqtts://username:password@my.broker.com:4711/dir

For more information visit: https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/protocols/mqtt.html

JSON Payload Structure (an example from AirGradient ONE)

{
  "pm01": 0,
  "pm02": 0,
  "pm10": 0,
  "pm01Standard": 0,
  "pm02Standard": 0,
  "pm10Standard": 0,
  "pm003Count": 129.83,
  "pm005Count": 116.17,
  "pm01Count": 18.17,
  "pm02Count": 2.33,
  "pm50Count": 0.33,
  "pm10Count": 0.33,
  "pm02Compensated": 0,
  "atmp": 26.61,
  "atmpCompensated": 26.61,
  "rhum": 42.91,
  "rhumCompensated": 42.91,
  "rco2": 397.33,
  "tvocIndex": 98.83,
  "tvocRaw": 30777.58,
  "noxIndex": 1,
  "noxRaw": 15251,
  "boot": 4,
  "bootCount": 4,
  "wifi": -47,
  "ledMode": "iaqs",
  "serialno": "34b7daa16674",
  "firmware": "3.7.0",
  "model": "I-9PSL"
}

---

Parameter	Meaning and unit	Presence
pm01	Atmospheric-environment PM1.0 mass concentration, µg/m³.	Valid PM reading
pm02	Atmospheric PM2.5 mass concentration, µg/m³. Despite the name, this means PM2.5, not PM2.0 or PM0.2.	Valid PM reading
pm10	Atmospheric PM10 mass concentration, µg/m³.	Valid PM reading
pm01Standard	PM1.0 “standard particle”/CF=1 mass concentration, µg/m³.	Valid sensor reading
pm02Standard	PM2.5 standard-particle mass concentration, µg/m³.	Valid sensor reading
pm10Standard	PM10 standard-particle mass concentration, µg/m³.	Valid sensor reading
pm02Compensated	Corrected PM2.5, µg/m³. It requires valid PM2.5 and humidity. The configured correction is used; with no configured algorithm, MQTT forces the built-in EPA correction.	Valid PM2.5 and RH
pm003Count	Particle count at the 0.3 µm threshold, particles per 0.1 L (#/dL). SPS30 does not supply this bin.	Sensor capability and valid reading
pm005Count	Particle count at the 0.5 µm threshold, #/dL.	Sensor capability and valid reading
pm01Count	Particle count at the 1.0 µm threshold, #/dL.	Sensor capability and valid reading
pm02Count	Particle count at the 2.5 µm threshold, #/dL.	Sensor capability and valid reading
pm50Count	Particle count at the 5.0 µm threshold, #/dL. Normally available from the indoor PMS5003, not PMS5003T.	Supported/populated bin
pm10Count	Particle count at the 10 µm threshold, #/dL. Normally available from PMS5003; a single-channel SPS30 configuration can also emit it.	Supported/populated bin
atmp	Uncorrected temperature in °C. On ONE it comes from SHT; on Open Air it normally comes from PMS5003T. SPS30 does not provide temperature.	Valid temperature
atmpCompensated	Corrected temperature in °C. On ONE it may equal atmp when no correction is configured; Open Air MQTT forces its standard PMS5003T correction when configured as none.	Valid temperature
rhum	Uncorrected relative humidity in percent. ONE uses SHT; Open Air normally uses PMS5003T.	Valid humidity
rhumCompensated	Corrected relative humidity in percent. It may equal the raw value on ONE when no correction is configured.	Valid humidity
rco2	Senseair S8 CO₂ concentration in ppm.	S8 detected and reading valid
tvocIndex	Dimensionless Sensirion VOC Gas Index calculated from SGP41 data.	SGP41 detected and reading valid
tvocRaw	Raw SGP41 VOC signal/ticks. This is not a ppb concentration.	SGP41 detected and reading valid
noxIndex	Dimensionless Sensirion NOx Gas Index.	SGP41 detected and reading valid
noxRaw	Raw SGP41 NOx signal/ticks, not a ppb concentration.	SGP41 detected and reading valid
boot	Counter since the current reboot. More precisely, v3.7.0 increments it before each enabled Wi-Fi cloud-post attempt; MQTT itself does not increment it.	Always
bootCount	Exact duplicate of boot, retained as a compatibility alias.	Always
wifi	Monitor Wi-Fi RSSI in dBm. A value nearer zero indicates a stronger signal.	Always
ledMode	Current ONE LED-bar mode: off, pm, co2, or iaqs.	AirGradient ONE only
serialno	Monitor device ID: normally the lowercase, colon-free Wi-Fi MAC-derived identifier. It is also used in the MQTT topic.	Always
firmware	Main device firmware build string. An official clean release reports 3.7.0.	Always
model	Runtime-detected hardware/sensor configuration.	Always
channels	Per-sensor measurements under keys "1" and "2". Used for dual-PM Open Air configurations.	O-1PP and O-1PPT
satellites	Optional map keyed by colon-free BLE satellite MAC. Each child contains atmp, rhum, and wifi; the child wifi is actually BLE RSSI in dBm.	Satellite support enabled and fresh data available

---

Product-Dependent Shape

• I-9PSL AirGradient ONE: flat payload, normally including PM, SHT temperature/humidity, CO₂, VOC/NOx, and ledMode.
• O-1PST one PM channel, CO₂, and VOC/NOx: flat payload.
• O-1PPT two PM channels and VOC/NOx: top-level aggregate plus channels.
• O-1PP two PM channels: top-level aggregate plus channels.
• 0-1PS one PM channel and CO₂: flat payload.
• O-1P one PM channel only: flat payload.

For dual-channel models, each top-level measurement is the average of channels 1 and 2 when both are valid. If only one is valid, the top-level value falls back to that channel.

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Important Behavior

• Missing or invalid sensor readings are omitted completely. There are no null placeholders.
• Measurements are rolling averages covering approximately the last 12 seconds, then rounded to at most two decimal places. They are not 60-second averages, even though MQTT publishes every 60 seconds.
• SPS30 has no atmospheric-versus-standard distinction, so firmware v3.7.0 puts the same SPS30 mass values into both sets of PM fields.
• MQTT does not contain cloud-only resetReason, freeHeap, or PM-sensor firmware fields.
• There is no timestamp or unit field.
• It uses the same JSON generator as the local endpoint GET /measures/current.