Sulphur dioxide level changed

The Sulphur dioxide level changed trigger fires after the sulphur dioxide (SO2) reading on one or more air quality sensors changes by a meaningful amount. Sulphur dioxide is a sharp-smelling gas released by burning fossil fuels (especially coal and oil), volcanic activity, and certain industrial processes. It irritates the respiratory system and contributes to acid rain. If you live near an industrial area, a power plant, or in a volcanically active region, SO2 levels are worth watching closely.

Imagine your outdoor vents sealing automatically when an industrial plume drifts your way, keeping that acrid air out of your home. Use this trigger to activate air filtration, close outdoor vents, or send notifications whenever your SO2 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 Sulphur dioxide 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.so2_changed. A basic example looks like this:

trigger: air_quality.so2_changed
target:
  entity_id: sensor.rooftop_so2
options:
  threshold: 5

This fires whenever the rooftop SO2 sensor reading changes by at least 5 ppb.

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

• Sulphur dioxide levels are most relevant near industrial areas, power plants, or regions with volcanic activity. Even moderate exposure irritates the throat and lungs.
• The trigger fires on any change that meets the threshold, whether the level goes up or down.
• To react only when SO2 crosses a specific concentration in one direction, use Sulphur dioxide 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: seal the house when SO2 shifts

If you live near an industrial site or in a volcanically active area, SO2 plumes drift in without warning. This automation closes the motorized vents when your outdoor SO2 sensor detects a significant change, keeping that acrid air out of your home.

• Trigger: Sulphur dioxide level changed
• Target: Rooftop SO2 sensor
• Threshold type: 5
• Action: Close cover

alias: "Close vents on SO2 change"
triggers:
  - trigger: air_quality.so2_changed
    target:
      entity_id: sensor.rooftop_so2
    options:
      threshold: 5
actions:
  - action: cover.close_cover
    target:
      entity_id: cover.fresh_air_vents

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:

• Sulphur dioxide level crossed threshold - Triggers after one or more sulphur dioxide levels cross a threshold.