What is time-integrated concentration (TIC) and why is it used?

What is time-integrated concentration (TIC) and why is it used?

• A. TIC is the time integral of concentration at a receptor, representing total exposure over a period and informing chronic risk assessment.
• B. TIC represents the average concentration over time.
• C. TIC is the peak concentration observed during the monitoring period.
• D. TIC is the total mass emitted.

Answer: (B)

Time-integrated concentration captures exposure over a defined period by integrating concentration at the receptor over that time. When you divide that time-integral by the duration, you obtain the average concentration during the interval. This average concentration is what’s often used in chronic risk assessments because it reflects the typical level of exposure people experience, not just brief spikes. The other ideas describe different things: a raw time integral without normalization represents total exposure, a peak concentration is the maximum level reached, and total mass emitted refers to the amount released from the source, not the concentration at the receptor over time.

Time-integrated concentration captures exposure over a defined period by integrating concentration at the receptor over that time. When you divide that time-integral by the duration, you obtain the average concentration during the interval. This average concentration is what’s often used in chronic risk assessments because it reflects the typical level of exposure people experience, not just brief spikes. The other ideas describe different things: a raw time integral without normalization represents total exposure, a peak concentration is the maximum level reached, and total mass emitted refers to the amount released from the source, not the concentration at the receptor over time.