PM2.5 level changed

The PM2.5 level changed trigger fires after the PM2.5 (particulate matter 2.5 micrometers or smaller) reading on one or more air quality sensors changes by a meaningful amount. PM2.5 is the most widely tracked particle size for indoor and outdoor air quality. Sources include cooking, candles, wildfires, traffic exhaust, and dust. These fine particles are small enough to reach deep into the lungs, making them especially relevant during wildfire season, allergy season, or anytime you want to keep tabs on what your family is breathing.

Imagine your windows closing automatically the moment outdoor particle levels jump during a nearby wildfire, keeping smoke outside where it belongs. Use this trigger to turn on an air purifier, close windows, or send an alert whenever your PM2.5 sensor reports a significant shift.

Using this trigger from the user interface

If you prefer building automations visually, Home Assistant walks you through this trigger step by step. You pick what to watch, tweak a few options, and save. No YAML knowledge required.

To use this trigger in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the When section, select Add trigger.
4. Select what you want to monitor. Under By target (see Targets), pick the area your air quality sensor is in (like your living room or bedroom). You can also select a floor, a device, a specific entity, or a label.
5. From the triggers shown for that target, select PM2.5 level changed.
6. Under Threshold type, set how much the level has to change before the trigger fires.
7. Select Save.

Options in the UI

Using this trigger in YAML

If you work directly in YAML, or you want to know exactly what Home Assistant does under the hood, this section has the technical reference. It lists the field names you use in YAML, their types, and which ones are required.

In YAML, refer to this trigger as air_quality.pm25_changed. A basic example looks like this:

trigger: air_quality.pm25_changed
target:
  entity_id: sensor.living_room_pm25
options:
  threshold: 10

This fires whenever the living room PM2.5 sensor reading changes by at least 10 micrograms per cubic meter.

Options in YAML

YAML sometimes provides additional options for more complex use cases that are not available through the UI.

Targets

This trigger supports targets. A target tells Home Assistant what the trigger should watch. You can point it at a single entityAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more], a device, an area, a floor, or a label, and Home Assistant watches every matching air_quality entity behind that target.

• Entity: one specific air_quality entity, such as air_quality.living_room.
• Device: every air_quality entity that belongs to a device.
• Area: every air_quality entity in a room or area.
• Floor: every air_quality entity on a floor.
• Label: every air_quality entity that shares a label.

You can also mix target types in one trigger. For example, combine a specific entity with an area to watch both at once.

Good to know

• PM2.5 is the particle size most commonly referenced in air quality indexes worldwide. A threshold of 5 to 15 μg/m³ suits most home automations.
• The trigger fires on any change that meets the threshold, whether the level goes up or down.
• To react only when PM2.5 crosses a specific concentration in one direction, use PM2.5 level crossed threshold instead.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, then change the state of the targeted entity to watch the trigger fire on your actual entitiesAn entity represents a sensor, actor, or function in Home Assistant. Entities are used to monitor physical properties or to control other entities. An entity is usually part of a device or a service. [Learn more].

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup.

Automation: close windows during wildfire season

When wildfire smoke rolls in, the last thing you want is to leave the windows open. This automation closes your motorized windows as soon as PM2.5 levels shift significantly, keeping smoke and fine particles outside where they belong.

• Trigger: PM2.5 level changed
• Target: Outdoor PM2.5 sensor
• Threshold type: 15
• Action: Close cover

alias: "Close windows on PM2.5 change"
triggers:
  - trigger: air_quality.pm25_changed
    target:
      entity_id: sensor.outdoor_pm25
    options:
      threshold: 15
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.living_room_windows

Still stuck?

The Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the trigger you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related triggers

These triggers work well alongside this one:

• PM2.5 level crossed threshold - Triggers after one or more PM2.5 levels cross a threshold.