**Explanation:**

Air pollutants are substances that are present in the air and have harmful effects on human health, the environment, or both. They can be natural or man-made and can be in the form of gases, particles, or biological materials. Ozone, carcinogens, pesticides, and metallic powders are all examples of air pollutants.

However, ozone is not considered a primary air pollutant. It is a secondary air pollutant, meaning it is not directly emitted into the atmosphere but is formed through chemical reactions involving other air pollutants. Ozone is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight.

**Primary Air Pollutants:**

Primary air pollutants are directly emitted into the atmosphere from sources such as vehicles, industrial processes, power plants, and natural sources. Some examples of primary air pollutants include:

1. **Carcinogens:** Carcinogens are substances that can cause cancer. They can be present in the form of gases, particles, or volatile organic compounds (VOCs). Examples of carcinogenic air pollutants include benzene, formaldehyde, and certain types of particulate matter.

2. **Pesticides:** Pesticides are chemicals used to kill or control pests such as insects, weeds, and fungi. When these chemicals are sprayed into the air, they can become air pollutants. Some pesticides can persist in the environment and have harmful effects on human health and ecosystems.

3. **Metallic Powders:** Metallic powders are fine particles of metals or metal compounds. They can be released into the air during various industrial processes such as metal refining, welding, and metal cutting. Metallic powders can have harmful effects on human health if inhaled.

**Secondary Air Pollutants:**

Secondary air pollutants are formed in the atmosphere through chemical reactions involving primary air pollutants. Examples of secondary air pollutants include:

- Ozone (O3): Ozone is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. While ozone itself is a harmful pollutant, it is considered a secondary pollutant because it is not directly emitted.

In conclusion, ozone is not considered a primary air pollutant because it is formed through chemical reactions involving other air pollutants. Carcinogens, pesticides, and metallic powders are all examples of primary air pollutants that can have harmful effects on human health and the environment.