An obvious initial thought would be to use a humidifier, which is meant to increase humidity by emitting water vapor into the air, to diffuse therapeutic essential oils.
You can add a few drops of essential oil to the water tank of your humidifier, but the real question is whether you should.
The big, viscous particles of essential oils might clog the filter or fan of a humidifier designed to produce only a very thin mist.
Oils with a high resin content tend to be the culprits in such cases. Crane also cautions against clogging a humidifier's tank with essential oils.
Essential oils, especially citrus-based ones, can corrode plastic humidifiers over time. And, heat from this device will dilute, modify, and possibly weaken essential oils.
Also, the device will diffuse thick and heavy essential oils, which will settle on clothing and furnishings. The residue is challenging to clear and unsanitary.
Healthline cautions that essential oils must be handled with care to be used safely. Additionally, they can be poisonous to animals (especially cats).
Overall, generally essential oils are safe to use in a diffuser, but doing so may damage the device or, at the at least, void the guarantee.