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 this condition 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 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 conditions shown for that target, select Nitrogen dioxide value.
6. Under Threshold type, set the NO2 level the condition checks against.
7. Under Condition passes if (see Behavior), pick Any or All.
8. 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, 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: 40
  behavior: any

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

Options in YAML

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

Targets

This condition supports targets. A target tells Home Assistant what the condition should check. 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 evaluates 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 condition. For example, combine a specific entity with an area to check both at once.

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 (unavailable) or have an unknown state (unknown) are skipped for Any and fail for All.
• 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.

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 at or 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: Air Quality: Nitrogen dioxide value
• Target: Outdoor NO2 sensor
• Threshold type: 40
• Condition passes if: Any
• Action: Notify: Send notification

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: 40
      behavior: any
actions:
  - action: notify.mobile_app_phone
    data:
      title: "High NO2 outside"
      message: >
        Outdoor NO2 is above 40. 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

These conditions work well alongside this one:

• 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.