What are vapors in the context of air quality?

Vapors, in the context of air quality, refer to gases that are generated by the evaporation of substances that are typically in liquid or solid form at room temperature. This definition highlights the transformation of materials as they change states due to varying temperatures or pressures.

Understanding this concept is crucial, especially in air quality management, as vapors can include volatile organic compounds (VOCs) and other pollutants that may adversely affect human health and the environment. These emissions can come from many sources, including paints, solvents, and other chemical products.

The other options do describe phenomena related to air quality, but they do not accurately define vapors. Heavy gases that trap heat refer more closely to greenhouse gases, while particles suspended in air relate to particulate matter. Fumes from combustibles in HVAC systems focus on specific emissions rather than the broader concept of vaporization from various materials. As such, the definition emphasizing the phase change of materials accurately captures the essence of what vapors are within the context of air quality.