Nitrogen dioxide level changed

The Nitrogen dioxide level changed trigger fires after the nitrogen dioxide (NO2) reading on one or more air quality sensors changes by a meaningful amount. Nitrogen dioxide is a reddish-brown gas with a sharp odor, produced mainly by traffic, power plants, and gas stoves. It irritates the airways and contributes to smog and acid rain. Indoors, your gas stove is often the biggest source. Every time you fire up a burner, NO2 levels in the kitchen rise.

Imagine your range hood turning on automatically when you start cooking, clearing combustion byproducts before they spread through the house. Use this trigger to start ventilation, close windows facing a busy road, or send a health alert whenever your NO2 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 Nitrogen 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.no2_changed. A basic example looks like this:

trigger: air_quality.no2_changed
target:
  entity_id: sensor.street_side_no2
options:
  threshold: 10

This fires whenever the street-side NO2 sensor reading changes by at least 10 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

• Indoor gas stoves and heaters are common sources of NO2 inside the home. A kitchen NO2 sensor combined with this trigger helps you automate range hood ventilation.
• The trigger fires on any change that meets the threshold, whether the level goes up or down.
• To react only when NO2 crosses a specific concentration in one direction, use Nitrogen 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: turn on the range hood when cooking produces NO2

Every time you fire up the gas stove, NO2 levels in the kitchen rise. This automation turns on the range hood as soon as the kitchen NO2 sensor detects a shift, clearing combustion byproducts before they spread through the house.

• Trigger: Nitrogen dioxide level changed
• Target: Kitchen NO2 sensor
• Threshold type: 15
• Action: Turn on switch

alias: "Range hood on NO2 change"
triggers:
  - trigger: air_quality.no2_changed
    target:
      entity_id: sensor.kitchen_no2
    options:
      threshold: 15
actions:
  - action: switch.turn_on
    target:
      entity_id: switch.range_hood

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:

• Nitrogen dioxide level crossed threshold - Triggers after one or more nitrogen dioxide levels cross a threshold.