What are volatile organic compounds (VOCs) primarily characterized by?

Volatile organic compounds (VOCs) are primarily characterized as chemical compounds that evaporate at normal room temperatures. This property is crucial because it determines their behavior in the environment, particularly in indoor air quality contexts. VOCs can easily transition from liquid to gas, leading to their release into the air we breathe. This volatility is significant because it impacts their concentration in indoor environments, influencing potential health effects and air quality.

In contrast, the other options do not align with the defining characteristics of VOCs. For example, stating that VOCs are chemical compounds that remain liquid at all temperatures does not accurately represent their nature, as many VOCs can exist as gases at typical indoor conditions. The idea of stability without state change is inconsistent with the volatile nature of these compounds, which readily evaporate. Lastly, claiming that VOCs contain no carbon is incorrect, since the "organic" in VOCs implies a carbon-containing structure. Thus, the essence of VOCs lies in their ability to evaporate at room temperature, which has significant implications for indoor air quality.