Sulphur dioxide value

The Sulphur dioxide value condition passes when a sulphur dioxide (SO2) sensor’s reading meets a specific level. SO2 is a sharp-smelling gas released by burning fossil fuels and volcanic activity. Elevated levels irritate the respiratory system and make outdoor air uncomfortable. This condition lets your automation respond to real readings, closing the windows and notifying you to stay indoors when SO2 is too high, and letting fresh air back in once the reading drops.

Using this condition from the user interface

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

To use Sulphur dioxide value in an automation:

1. Go to Settings > Automations & scenes.
2. Open an existing automation, or select Create automation > Create new automation.
3. In the And if section, select Add condition.
4. Select what you want to check. Under By target (see Targets), pick the area your sulphur dioxide sensor is in (like your garden or balcony). You can also select a device, a specific entity, or a label.
5. From the conditions shown for that target, select Sulphur dioxide value.
6. Under Threshold type, set the level the condition checks against:
   1. Pick whether the reading must be Above, Below, In range, or Outside range of the threshold.
   2. Select Number or Entity:
      • Number: Enter a fixed level directly, for example 40. For In range or Outside range, enter both a lower and upper bound.
      • Entity: Use a sensor entity or a number helper entity as the threshold:
        • Number helper: You can adjust the threshold value without editing the automation. The sensor reading is compared against the number helper’s current value.
        • Sensor: Its current reading becomes the threshold and updates automatically as the sensor changes.
        • For In range or Outside range, you need two entities: one for the lower bound and one for the upper bound (for example, two separate number helpers).
        • If you don’t have a number helper, you can create one by selecting Create a new number helper.
7. Under Unit, select the concentration unit (ppb or μg/m³) to use for the threshold comparison.
8. Under Condition passes if (see Behavior), pick Any or All.
9. Select Save.

Options in the UI

Using this condition 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. For how an automation is built in YAML, refer to Automations in YAML.

In YAML, put the settings that are specific to this condition under options. Keep target, if the condition uses one, and general settings such as alias and enabled at the top level, next to condition.

In YAML, refer to this condition as air_quality.is_so2_value. A basic example looks like this:

condition: air_quality.is_so2_value
target:
  entity_id: sensor.outdoor_so2
options:
  threshold:
    type: above
    value:
      number: 40
      unit_of_measurement: "μg/m³"
  behavior: any

This passes when the outdoor SO2 sensor reads above 40 μg/m³.

Options in YAML

threshold:
  type: between
  value_min:
    entity: input_number.so2_alert_level
  value_max:
    number: 20
    unit_of_measurement: "μg/m³"

Targets of the condition

This condition requires a target. The target is the object that Home Assistant will check. You can point the condition 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 will evaluate every matching sulphur dioxide sensor behind that target.

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

You can also select different target types in one condition. For example, you can add a specific entity and an area as targets in the same condition to check 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.

Behavior with multiple targets

When you target more than one entity (or select an area, floor, or label that contains several), the Condition passes if option controls how the results combine:

• Any (default): the condition passes if at least one of the targeted entities matches. For example, if you check three smoke sensors and only one of them detects smoke, the condition still passes. This is useful for questions like “is there smoke anywhere in the house?”
• All: the condition passes only when every targeted entity matches. For example, if you check the same three smoke sensors, the condition passes only once all three report cleared. This is useful for “is the entire house safe now?” checks, so your automation does not send an all-clear while one room still has a reading.

Good to know

• Sensors that are unavailable or unknown are skipped. With Any, the condition passes if at least one of the other targeted sensors matches. With All, it passes if all the other targeted sensors match. If all targeted sensors are unavailable or unknown, All passes and Any fails.
• For related pollutant conditions, see Nitrogen dioxide value and Ozone value.

Try it yourself

Ready to test this? Go to Settings > Automations & scenes, open an automation, and add this condition. Trigger the automation with and without the condition met, and watch whether it continues or stops.

More examples

Real scenarios where this condition gates an automation. Copy any example and adapt it to your setup. In the visual editor, select the UI options listed in the example or paste the YAML code.

Automation: warn you before heading outside in the morning

If you live near an industrial area, SO2 readings sometimes spike overnight. This automation triggers at 7:00 AM and checks the outdoor SO2 level. If the reading is above 40 μg/m³, you get a notification recommending you stay indoors. On mornings with clean air, you can leave without interruption.

• Trigger: Time: 07:00
• Condition: Sulphur dioxide value
  • Target: Outdoor SO2 sensor
  • Threshold type: Above 40 μg/m³
  • Condition passes if: Any
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Morning SO2 warning"
triggers:
  - trigger: time
    at: "07:00:00"
conditions:
  - condition: air_quality.is_so2_value
    target:
      entity_id: sensor.outdoor_so2
    options:
      threshold:
        type: above
        value:
          number: 40
          unit_of_measurement: "μg/m³"
      behavior: any
actions:
  - action: notify.send_message
    target:
      entity_id: notify.my_device
    data:
      title: "SO2 is high outside"
      message: >
        Outdoor SO2 is above 40 μg/m³. Consider
        staying indoors this morning.

Still stuck?

To find out why the condition didn’t pass, check it live in the automation editor, and look at the trace of the run. For details, refer to Testing automations. For common problems and their solutions, refer to Troubleshooting automations.

If that doesn’t help, the Home Assistant community is quick to help: join Discord for real-time chat, post on the community forum with the condition you’re using and what you expected to happen, or share on our subreddit /r/homeassistant.

Related conditions

Explore related conditions:

• Nitrogen dioxide value: Tests the nitrogen dioxide level of one or more entities.

• Ozone value: Tests the ozone level of one or more entities.