Co-movement patterns: the fingerprint catalog

Watching CO₂ in isolation tells you what CO₂ is doing. Watching CO₂, VOC, NO_x, PM_2.5, humidity, and temperature together tells you what's happening. This article is a small library of those co-movement fingerprints, to help you read your own charts.

Gas-stove cooking: NO_x and PM_2.5 rise together within seconds of ignition. VOCs follow within 1-2 minutes. Humidity rises gently from water vapor. CO₂ rises if the kitchen is closed. Hood-on flattens NO_x and PM dramatically; hood-off leaves all four elevated for the duration. Recovery: 30-60 minutes after cooking ends.

Bedroom overnight: CO₂ climbs slowly and monotonically. RH climbs slowly too. PM stays flat. VOCs and NO_x stay flat. The shape is distinctive: a near-linear ramp lasting 6-8 hours, ending in a sharp drop when the door opens.

Candles or incense: PM_2.5 rises with a mild VOC accompaniment; with candles the jump is largest just after lighting and when they are snuffed out. The NO_x index can tick up slightly, because candle flames emit some NO and NO₂. CO₂ barely moves. Cleaning products: sharp VOC spike, everything else flat. Wildfire smoke event: PM_2.5 elevated for hours, mild VOC tail, NO_x mildly elevated, CO₂ flat, outdoor PM correlated.

Terrestream names a likely source only in a few cases, based on the room type you chose at setup and on which readings rose together or one after another, and it usually hedges: a VOC rise that spreads from the kitchen into a bedroom is titled "Cooking may be reaching bedrooms," VOC and NO_x climbing together above the room's usual levels is a "Possible combustion-related change," and CO₂ that keeps building after a VOC spike reads "CO₂ rising after cooking." It names cleaning only when you have reported it. Otherwise a notification says what rose and in which room and suggests checking for a nearby source, and in the app you can mark what the source was. Its wildfire-smoke alerts come from outdoor data (satellite smoke maps, fire detections, wind, and outdoor PM_2.5), not from the indoor pattern. This catalog is for reading the charts yourself.