What specific component defines volatile organic compounds (VOCs)?

Volatile organic compounds (VOCs) are specifically identified by their ability to participate in photochemical reactions. These compounds are characterized by their volatility, meaning they easily vaporize into the air, especially at room temperature. When these compounds are released into the atmosphere, they can react with other substances, often leading to the formation of ground-level ozone and other secondary pollutants through photochemical processes. This reactivity is a significant concern in environmental regulations and air quality management, making it essential to examine their roles in photochemical reactions when understanding VOCs.

The other choices do not accurately capture the defining characteristics of VOCs. For instance, while many carbon compounds are indeed classified as VOCs, not all fall under this designation as some may not be volatile or reactive in a photochemical sense. Additionally, VOCs encompass a wide range of organic compounds used in various applications beyond pesticides, so limiting the definition solely to pesticide applications is too restrictive. Lastly, while it is true that some VOCs may emit strong odors, this is not a definitive characteristic, as there are many VOCs that are odorless or have very faint smells yet still exhibit volatility and reactivity.