SCIENCE · INVESTIGATE AND EXPLAIN

Separate penetration and generation in a steady particle balance

Indoor particles can originate outdoors or be generated inside. Penetration, air exchange, deposition, filtration and activity all affect a concentration. A lower outdoor reading alone cannot identify an indoor source contribution, and an indoor/outdoor ratio is not itself a health-risk measure.

Learning outcome: Hold generation fixed while changing penetration, then hold penetration fixed while changing generation. Identify which observation would distinguish the two proposed source explanations.

Starting recap

Retain observation history, units, temporal coverage and model assumptions; distinguish a conditional reconstruction from detected or attributed environmental change.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

At penetration 0.6 and indoor generation 10 µg/(m³ hour), the outdoor contribution is 9 and indoor contribution 10 µg/m³. Total 19, indoor-source fraction 10/19≈0.526 and indoor/outdoor ratio 19/30≈0.633.

Open the experiment

Predict

Changing penetration at fixed air exchange changes:

Your prediction and reason

Experiment

Hold generation fixed while changing penetration, then hold penetration fixed while changing generation. Identify which observation would distinguish the two proposed source explanations.

Separate outdoor penetration from an indoor source

Worked teaching model · synthetic values · Original steady well-mixed room: outdoor concentration 30µg/m³, air exchange 0.5/hour and additional deposition/removal 0.5/hour. C=(0.5×penetration×30+indoor generation)/(0.5+0.5). Fixed coefficients, no resuspension, chemistry, spatial gradients or personal health prediction.

Particle penetration fraction: 0.6 fraction Indoor generation per room volume: 10 µg/(m³ hour)

Reset keeps your prediction, captures and practice history.

Original synthetic system; units differ by row
Quantity	Value	Unit
Outdoor-source steady contribution	9	µg/m³
Indoor-source steady contribution	10	µg/m³
Total modeled indoor concentration	19	µg/m³
Indoor-source fraction of total	0.5263158	fraction
Indoor / outdoor concentration ratio	0.6333333	ratio

Outdoor concentration alone cannot determine indoor concentration when sources and losses differ.

This constant-coefficient balance does not identify actual source composition, room mixing or personal risk. A source intervention and a penetration change target different terms; changing ventilation would affect both entry and removal and is not this control.

Predict, change one control, and save contrasting captures. Reconstruct the balance with units; then explain a process the ledger deliberately leaves out. Display precision is not measurement precision.

Outdoor concentration alone cannot determine indoor concentration when sources and losses differ.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Define the evidence question

Reconstruct the observation or physical model

The original well-mixed room has outdoor concentration 30 µg/m³, exchange 0.5 per hour and additional removal 0.5 per hour. Outdoor entry per volume is exchange×penetration×outdoor concentration; indoor generation adds another rate. At equilibrium, total input equals concentration×the sum of removal rates.

Separate the competing interpretations

The model therefore gives C=15 P+G because the total loss coefficient is 1 per hour. The two steady contributions can be displayed separately. Penetration changes outdoor entry; changing air exchange would alter both entry and removal and is not the same operation. No physical ventilation intervention is requested.

Challenge uncertainty and identification

Particle size and composition, imperfect mixing, intermittent sources, resuspension and surface chemistry can invalidate this simple comparison. A real source assessment needs measurements and appropriate professional interpretation. The model does not prescribe filters, operating conditions or a personal safe concentration.

Worked original packet

Investigation

Hold generation fixed while changing penetration, then hold penetration fixed while changing generation. Identify which observation would distinguish the two proposed source explanations.

Changed-case transfer

At penetration 0.4 and generation 20, calculate concentration and indoor-source fraction.

Feedback

Outdoor contribution 6 plus indoor 20 gives 26 µg/m³; indoor-source fraction 20/26≈0.769. The room remains below outdoor 30 despite most modeled indoor concentration coming from its indoor source.

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.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

At penetration 0.4 and generation 20, calculate concentration and indoor-source fraction.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Keep peak and duration visible beside an exposure average Next: Distinguish radiative forcing from transient and equilibrium response

Save a science backup or import one

Science work is stored locally in this browser, separately from mathematics and AI. It does not sync automatically. Use this science-only backup; this checkout's older all-subject export does not include science.

A legacy file is available only when the complete snapshot fits the 36 MB limit. For larger snapshots, prepare a complete file set below; never discard notebooks to make a smaller file.

Choose a science backup (maximum 36 MB)

Matching imported notebook drafts replace their current drafts. Omitted lessons and known first attempts remain. Export your current work first if you want to retain both drafts.

Complete file sets and course backups

A file set can hold more work than one science file. Keep its manifest and every part together. Each file is limited to 36 MB. This format needs this version of LearnAI or a compatible newer version; older versions can use only the legacy single-file backup above.

Export scope

The set includes every saved science course and global continuation at this moment. Later edits need a new export. A conflicting tab exports its own visible work, which may differ from saved work in another tab.

Choose the manifest and all parts together

0 file(s) selected. File order and filenames do not determine identity. Missing, changed or conflicting parts block the entire restore; no good part is applied by itself.

Science storage: loading. No account or remote computation is required.