Ionization smoke detectors are designed to detect what type of combustion particles?

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Ionization detectors are tuned to respond to the smallest combustion particles. They use a small amount of radioactive material to ionize the air; when smoke particles enter, these ions are neutralized by the particles, reducing the electrical current and triggering the alarm. Those tiny, subvisible particles from flaming fires are what cause this change, so the detector is best described as detecting particles too small to be seen with the naked eye. Large visible particles and dust don’t influence the ionization current in the same reliable way, and gases from combustion aren’t the primary signal for ionization detectors.