Datum spirabilis

what is it

Three years of Seoul air quality. Not one creature but a species in twenty-five specimens, one per monitoring station. This is the air a million and a half people breathed, measured every hour by instruments that sometimes failed.

how is it made

The growth angle is the photochemical regime against the combustion regime, where sunlight and traffic pull the air in opposite directions: a real measured chemical compass. Fine particles drive step length, coarse dust drives thickness, sulphur sets the colour. A heavy smog day is a shock.

what to look for

• A chemical compass. direction is a real bipolar measured field, not a calendar trick: among the purest direction signals in the project.
• Twenty-five siblings. one species, twenty-five specimens. Each station grows its own creature from the same three years.

the honest part

The direction is a real chemical compass, sunlight pulling against traffic, and that is its strength. The catch is that it is built from three pollutants folded into one index rather than a single clean measurement. Stronger than a calendar season like sanguinaria's, not quite as pure as the single measured wind in ventosa.