Keep peak and duration visible beside an exposure average

Define the evidence question

Environmental exposure describes contact with an agent over time; concentration, duration and frequency are different dimensions. An average can summarize a profile but erase its peaks and timing. A concentration at a monitor also need not equal the concentration at a person’s actual location.

Reconstruct the observation or physical model

The fictional 24-hour profile has a hours at concentration b and the remaining hours at 10 µg/m³. The concentration-time integral is ab+(24−a)10, with units µg·hour/m³. Dividing by 24 gives the time-weighted concentration; the peak is b. This is not a mass dose because no inhaled volume or uptake has been supplied.

Separate the competing interpretations

Different profiles can share the same integral and average. Two hours at 100 with 22 at 10 and six hours at 40 with 18 at 10 each integrate to 420 and average 17.5 µg/m³, but have different peaks and durations. They should not automatically be treated as biologically equivalent.

Challenge uncertainty and identification

Actual exposure assessment may need activity, breathing rate, route, uptake, susceptibility and a relevant time window. This teaching packet supplies none of the evidence needed for a personal health-risk calculation or safety threshold. It is a dimensional comparison, not medical advice or a recommendation to enter polluted locations.

Worked original packet

Four hours at 60 and twenty at 10 integrate to 440 µg·hour/m³. The 24-hour average is 18.333 µg/m³ and peak 60. None is automatically an absorbed dose.

Investigation

Find two supported profiles with the same average but different peaks. Keep their complete duration records and explain what biological or location evidence would be needed before comparing effects.

Changed-case transfer

Compare 2 hours at 100 with 6 hours at 40; calculate both integrals and averages.

Feedback

Both integrals are 420 µg·hour/m³ and averages 17.5 µg/m³. Peaks 100 and 40 and durations 2 and 6 differ; equal integrated concentration does not establish equal absorbed dose or effect.

Sources and evidence boundary

Original prose, numerical packets and exercises. Primary method/mechanism source, checked 30 October 2026. No current measured climate values, personal risk estimates, exposure limits or regulatory conclusions are inferred from these fictional cases. Retain first reasoning and critique in the course workspace. No physical pollutant exposure or environmental intervention is requested.