What type of air is used for pressurization?

The correct answer is intermediate pressure air (IP air), which is essential for pressurization in various systems, particularly in aviation. This type of air is used because it strikes a balance between being sufficiently pressurized for effective operation while ensuring safety and efficiency in system design.

Intermediate pressure air often comes from compressors or other sources within an aircraft's systems and is prepared to meet specific requirements for functions such as cabin pressurization and pneumatic system operations. The use of IP air ensures that the systems can maintain appropriate operational pressure without the complications associated with higher pressures, which could lead to structural stress or the need for more robust components.

Filtered air may be necessary for certain applications, ensuring that contaminants are removed, but it does not inherently possess the pressure characteristics needed for the effective pressurization processes. High-pressure air typically refers to air stored at very high pressures, which may be used in specific applications but is less common for general pressurization. Ground air can also reference air brought from external sources during maintenance before flight but lacks the specific capacity and management necessary for effective pressurization once the aircraft is in operation.

Thus, IP air is classified as the ideal choice for pressurization needs, making it the correct option in this context.