Nitrogen dioxide value

The Nitrogen dioxide value condition passes when a nitrogen dioxide (NO2) sensor’s reading meets a specific level. NO2 is a reddish-brown gas that comes from traffic and combustion, and elevated levels irritate the airways. This condition helps your automation make informed decisions about outdoor air, for example holding off on opening the windows during rush hour or sending you a notification recommending indoor exercise when NO2 is too high.

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 Nitrogen 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 nitrogen dioxide sensor is in (like your garden or kitchen). You can also select a device, a specific entity, or a label.
5. From the conditions shown for that target, select Nitrogen 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, ppm, 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.

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_no2_value. A basic example looks like this:

condition: air_quality.is_no2_value
target:
  entity_id: sensor.outdoor_no2
options:
  threshold:
    type: above
    value:
      number: 40
      unit_of_measurement: "μg/m³"
  behavior: any

This passes when the outdoor NO2 sensor reads above 40 μg/m³.

Options in YAML

threshold:
  type: between
  value_min:
    entity: input_number.no2_alert_level
  value_max:
    number: 25
    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 nitrogen dioxide sensor behind that target.

• Entity: one specific nitrogen dioxide sensor, such as sensor.living_room_nitrogen_dioxide.
• Device: every nitrogen dioxide sensor that belongs to a device.
• Area: every nitrogen dioxide sensor in a room or area.
• Floor: every nitrogen dioxide sensor on a floor.
• Label: every nitrogen 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 pollutants, see Nitrogen monoxide value, Nitrous oxide 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: suggest indoor exercise before your morning run

If you have a daily running routine, you want to know whether the outdoor air is safe before heading out. This automation triggers at 6:30 AM and checks whether outdoor NO2 is above 40 μg/m³. If it is, you get a friendly suggestion to exercise indoors instead. On clean-air mornings, you never hear a thing and head out as usual.

• Trigger: Time: 06:30
• Condition: Nitrogen dioxide value
  • Target: Outdoor NO2 sensor
  • Threshold type: Above 40 μg/m³
  • Condition passes if: Any
• Action: Send a notification message
  • Target: My Device (notify.my_device)

alias: "Suggest indoor exercise on high NO2"
triggers:
  - trigger: time
    at: "06:30:00"
conditions:
  - condition: air_quality.is_no2_value
    target:
      entity_id: sensor.outdoor_no2
    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: "High NO2 outside"
      message: >
        Outdoor NO2 is above 40 μg/m³. Consider
        exercising indoors today.

Still stuck?

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 monoxide value: Tests the nitrogen monoxide level of one or more entities.

• Nitrous oxide value: Tests the nitrous oxide level of one or more entities.

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