PM1 level changed

The PM1 level changed trigger fires after the PM1 (particulate matter 1 micrometer or smaller) reading on one or more air quality sensors changes. PM1 particles are ultrafine and originate from combustion, vehicle exhaust, and industrial emissions. Because of their tiny size, they penetrate deep into the lungs and bloodstream. Cooking on a gas stove, nearby traffic, or a wildfire miles away all push PM1 levels up inside your home.

Imagine your nursery air purifier ramping up the moment particle levels shift, keeping the air as clean as possible for little ones without you doing anything. Use this trigger to start an air purifier, adjust HVAC filtration, or log particle count changes. Use the threshold type to filter which changes matter to your automation.

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 PM1 level changed 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 PM1 sensor is in (like your living room or bedroom). You can also select a device, a specific entity, or a label. When you target multiple entities (via area, label, or multiple entity selections), the trigger fires whenever any of them changes.
5. From the triggers shown for that target, select PM1 level changed.
6. Under Threshold type, configure what kind of change fires the trigger:
   • Select Any change to fire on any change, regardless of direction or new value.
   • Select Above or Below and enter a value to fire only when the new reading is above or below that value.
   • Select In range and enter a lower and upper bound to fire only when the new reading falls inside the range.
   • Select Outside range and enter a lower and upper bound to fire only when the new reading is outside the range.
   • For each option, you can enter a fixed level in μg/m³, pick a sensor entity or a number helper entity as the threshold.
     • If you don’t have a number helper, you can create one by selecting Create a new number helper.
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, put the settings that are specific to this trigger under options. Keep target, if the trigger uses one, and general settings such as id, alias, enabled, and variables at the top level, next to trigger.

When this trigger starts an automation, it passes data about what happened to the automation. You can use this trigger data in the templates of your conditions and actions. To see which data is available, refer to Trigger data in templates.

In YAML, refer to this trigger as air_quality.pm1_changed. A basic example looks like this:

trigger: air_quality.pm1_changed
target:
  entity_id: sensor.living_room_pm1
options:
  threshold:
    type: above
    value:
      number: 5

This fires whenever the living room PM1 sensor reading changes to a value above 5 μg/m³. To fire on any change, use type: any and leave out value.

Options in YAML

Targets of the trigger

This trigger requires a target. The target is the object that Home Assistant will watch. You can select 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 as a target, and Home Assistant will watch every matching PM1 sensor behind that target.

• Entity: one specific PM1 sensor, such as sensor.living_room_pm1.
• Device: every PM1 sensor that belongs to a device.
• Area: every PM1 sensor in a room or area.
• Floor: every PM1 sensor on a floor.
• Label: every PM1 sensor that shares a label.

You can also select different target types in one trigger. For example, you can add a specific entity and an area as targets in the same trigger to monitor both of them at once.

To learn which entities Home Assistant includes for a device, area, floor, or label, and how it handles several entities, refer to Automation targets.

Trigger variables

When the trigger reacts, the trigger variable identifies the entity that made it react. This is useful when a target contains multiple entities, such as a device, area, floor, or label.

The following trigger-specific variables are available:

• trigger.entity_id: Entity ID of the entity that made the trigger react.
• trigger.from_state: Previous state object of that entity.
• trigger.to_state: New state object of that entity.
• trigger.for: Timedelta object of how long the trigger criteria were met, if applicable.

For example, use {{ trigger.to_state.name }} in an action to include the name of the entity that made the trigger react in a notification.

The trigger variable describes the entity that made the trigger react. It doesn’t contain all the entities of the target.

Good to know

• PM1 particles are the smallest commonly measured particulate matter. They are especially relevant for respiratory health.
• The threshold type controls which changes fire the trigger. Use Above or Below to fire only when the new level is above or below a value, In range to fire only when it’s inside a range, and Outside range to fire only when it’s outside a range. Use Any change to fire on every change.
• To react only when PM1 crosses a specific concentration in one direction, use PM1 level crossed threshold instead.
• The threshold is in μg/m³. A sensor that reports PM1 in another unit never matches. If you use an entity as the threshold, it must also report μg/m³.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, create a new automation, and add this trigger. Save the automation, and then make the trigger react. For example, change the state of the targeted 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], turn on a light that the trigger monitors, or change its brightness. To check whether the automation ran, open its traces.

More examples

Real scenarios where this trigger fires in automations and scripts. Copy any example and adapt it to your setup. In the visual editor, select the UI options listed in the example when they are available, or paste the YAML code.

Automation: boost the air purifier when PM1 shifts

Ultrafine particles from cooking or traffic drift into every room, and tiny lungs are the most vulnerable. This automation increases your air purifier speed whenever PM1 levels in the nursery change to a value above 5 μg/m³, keeping the air as clean as possible for little ones.

• Trigger: PM1 level changed
  • Target: Nursery PM1 sensor
  • Threshold type: Above 5 μg/m³
• Action: Set fan speed
  • Target: Nursery air purifier
  • Percentage: 80%

alias: "Boost purifier on PM1 change"
triggers:
  - trigger: air_quality.pm1_changed
    target:
      entity_id: sensor.nursery_pm1
    options:
      threshold:
        type: above
        value:
          number: 5
actions:
  - action: fan.set_percentage
    target:
      entity_id: fan.nursery_air_purifier
    data:
      percentage: 80

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

Explore related triggers:

• PM1 level crossed threshold: Triggers when one or more PM1 levels cross a threshold.