Which of the following is NOT a factor that can influence residence time in environmental compartments?

• A. Temperature
• B. The volume of the compartment
• C. The color of the pollutant
• D. Reaction rates

Answer: (C)

Residence time is the average time a pollutant spends in a given environmental compartment before it leaves or is transformed. It hinges on how quickly the pollutant is removed or diluted. Temperature changes the speed of chemical and biological reactions; higher temperature generally increases degradation and lowers residence time. The volume of the compartment matters because, with the same inflow and outflow, a larger volume dilutes the pollutant more slowly and increases the time it stays there (tau is often thought of as V divided by Q, the flow rate). Reaction rates directly control how fast the pollutant is broken down or removed; faster rates shorten residence time, slower rates lengthen it. The color of the pollutant, on the other hand, does not influence these transport or reaction processes, so it does not affect residence time.