What is the SI unit of exposure in air?

The correct answer is Air Kerma, which is the SI unit specifically designed to quantify exposure to ionizing radiation in air. Air Kerma measures the kinetic energy released in air per unit mass due to the interactions of ionizing radiation, which is crucial for understanding the dose of radiation that can potentially affect living tissues.

Unlike Gray, which is the SI unit for absorbed dose in any material and not limited to air, Air Kerma focuses on air as the medium, making it more relevant for contexts where radiation exposure occurs in the atmosphere or surrounding environments. Similarly, the Sievert is used to measure the biological effect of ionizing radiation, which considers the quality of radiation and its impact on human health rather than just the raw exposure measurement in air. The Becquerel, on the other hand, is a unit used to measure radioactivity, representing the decay of radioactive material over time, but it does not directly relate to the exposure of radiation in air.

Therefore, Air Kerma is the most appropriate unit for quantifying exposure to ionizing radiation specifically in air.