What does a flow-weighted average concentration represent in composite samples?

What does a flow-weighted average concentration represent in composite samples?

• A. The maximum sub-sample concentration observed.
• B. The minimum sub-sample concentration observed.
• C. The combined concentration reflecting the contribution of each sub-sample over time.
• D. The simple arithmetic mean ignoring sampling duration.

Answer: (C)

Flow-weighted average concentration represents the overall pollutant level in a composite sample by accounting for how much flow each sub-sample represents over time. Periods with higher flow contribute more to the average because they carry more total volume (and potentially more pollutant mass). Conceptually, you weight each sub-sample’s concentration by the flow (or by the time it’s representing), sum those weighted values, and divide by the total flow (or total time). This yields an average that reflects the actual mass of pollutant transported during the sampling period, not just a simple equal-average of concentrations. It’s distinct from the maximum or minimum values, which ignore duration and flow, and from a simple arithmetic mean that treats all sub-samples as equally representative regardless of how much flow occurred.

Flow-weighted average concentration represents the overall pollutant level in a composite sample by accounting for how much flow each sub-sample represents over time. Periods with higher flow contribute more to the average because they carry more total volume (and potentially more pollutant mass). Conceptually, you weight each sub-sample’s concentration by the flow (or by the time it’s representing), sum those weighted values, and divide by the total flow (or total time). This yields an average that reflects the actual mass of pollutant transported during the sampling period, not just a simple equal-average of concentrations. It’s distinct from the maximum or minimum values, which ignore duration and flow, and from a simple arithmetic mean that treats all sub-samples as equally representative regardless of how much flow occurred.