What Is Compressed Air Made Of?

Compressed air is made of largely the same components as atmospheric air:

• About 78% nitrogen
• 21% oxygen
• 1-2% of other gases (like argon and carbon dioxide)

The only difference is that compressed air comes in a more condensed form. Still, the quality and composition of compressed air directly impact equipment performance, product quality, and operational efficiency in industrial settings.

This guide explains what makes up compressed air in more detail. We’ll then discuss how its composition can vary and why this matters for industrial applications.

The Basic Composition of Compressed Air

Compressed air maintains essentially the same chemical makeup as the air we breathe, just squeezed into a smaller volume. The compression process doesn’t fundamentally change the ratio of gases present in atmospheric air.

The main components include:

• Nitrogen: approximately 78%, acts as an inert carrier gas
• Oxygen: about 21% of the mixture, responsible for supporting combustion
• Trace gases (argon, carbon dioxide, neon, helium, etc.): 1-2%

This composition remains consistent regardless of the compression level. Only the density of these gases changes as they’re forced into a smaller space, which creates the pressure that makes compressed air so useful for industrial uses.

While we often refer to “compressed air” in industrial contexts, what we’re really talking about is atmospheric air that has been pressurized using mechanical means. The compression doesn’t create new substances but rather changes the physical state of existing air components.

Common Misconceptions About Compressed Air

Many people confuse compressed air with “canned air” products used for cleaning electronic equipment. Despite their name, these products don’t actually contain air at all.

Commercial dusters labeled as “compressed air” typically contain hydrofluorocarbons (like 1,1-difluoroethane) or hydrocarbon alkanes (such as butane and propane).

These chemicals are chosen for their properties that allow them to be stored as liquids under pressure and expelled as gas when released.

Another misconception is that compressed air is stored as a gas in industrial systems. In reality, the air is compressed so much that it behaves more like a liquid under pressure.

When this highly pressurized air is released, it expands rapidly and cools significantly due to the Joule-Thomson effect. This property makes it useful for industrial applications that require cooling effects.

Contaminants and Purification in Compressed Air Systems

While compressed air starts with the same composition as atmospheric air, the compression process can introduce several contaminants. These impurities can cause issues like:

• Damaging equipment
• Compromising product quality
• Creating health hazards

The compression process naturally concentrates any particulates present in the ambient air, such as:

• Dust
• Pollen
• Microorganisms

The mechanical compression process itself can also introduce metal particles and other debris from the compressor components.

Oil is a significant concern in many compressed air systems. Unless special oil-free compressors are used, trace amounts of lubricating oil often find their way into the compressed air stream.

This oil contamination can be particularly problematic in industries like:

• Food production
• Pharmaceutical manufacturing
• Electronics production

Water vapor is another notable challenge. Atmospheric air naturally contains humidity, and the compression process concentrates this moisture. As compressed air cools after compression, this moisture condenses into liquid water, potentially causing corrosion, freezing in lines, or product contamination.

High-quality compressed air systems use multiple purification stages to address these issues. For example:

• Particulate filters remove solid contaminants.
• Coalescing filters capture oil aerosols.
• Desiccant or refrigerated dryers reduce moisture content.
• Activated carbon filters remove odors and vapors for sensitive applications.

The degree of purification needed depends entirely on the end use. Semiconductor manufacturing requires ultra-pure compressed air, while operating pneumatic tools may tolerate higher levels of contaminants without issue.

Quality Standards for Compressed Air

The purity of compressed air is governed by international standards, with ISO 8573-1 being the most widely recognized classification system. This standard defines purity classes for key contaminants:

• Particles: the standard measures both the size and quantity of solid contaminants. Class 1 represents the highest purity (fewest particles), while Class 9 indicates the lowest purity level. Each class specifies maximum allowable particle counts across different size ranges.
• Water content: measured either as pressure dew point (the temperature at which moisture begins to condense) or concentration. Lower dew points indicate drier air with less moisture content, which is crucial for preventing condensation in pipelines.
• Oil: contamination limits cover both liquid oil and oil vapors. For critical applications like food processing or pharmaceuticals, oil content often must be kept below 0.01 mg/m³, corresponding to Class 1.

Beyond these three main categories, additional specifications can address other contaminants like microorganisms or specific gases, depending on the application requirements.

For example, hospitals use medical-grade compressed air that must meet stringent purity standards. This air often requires additional filtration beyond what typical industrial systems provide, removing nearly all microbiological contaminants and maintaining precise humidity levels.

Food and beverage production facilities typically require Class 1 or 2 air quality to prevent product contamination. These industries often install point-of-use filters as an additional safeguard right before the compressed air contacts food products.

Applications and Importance of Compressed Air Composition

The composition and purity of compressed air directly impact its suitability for different industrial applications.

In manufacturing environments, compressed air often comes into direct contact with products, so it must be exceptionally pure. For example, electronics manufacturing requires extremely clean, dry air to prevent microscopic damage to sensitive components. Even tiny oil droplets or water vapor can ruin circuit boards or interfere with coating processes.

For food and pharmaceutical industries, compressed air purity is a matter of regulatory compliance and consumer safety. These sectors typically require oil-free compression systems and multiple stages of filtration to prevent contamination from reaching the final product.

Medical applications demand the highest purity levels. Compressed air used in surgical tools, breathing apparatus, or laboratory equipment must be virtually free of all contaminants. Specialized medical air systems include redundant filtration and monitoring equipment to maintain these standards.

Air quality matters even in less sensitive applications like operating pneumatic tools in an auto shop. Excessive moisture or oil can:

• Damage tools
• Affect paint finishes
• Create slippery conditions

The energy efficiency of compressed air systems also relates directly to composition. Removing excess moisture and contaminants reduces pressure drops in the system, improving overall efficiency and reducing operational costs.